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Mechanisms of Metaprogramming @JakeWharton

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Metaprogramming

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Metaprogramming Runtime

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Metaprogramming Runtime Compile-time vs.

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Metaprogramming Runtime Compile-time vs. Additive

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Metaprogramming Runtime Compile-time vs. Additive Mutating vs.

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Metaprogramming Runtime Compile-time Additive Mutating

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Metaprogramming Runtime Compile-time Additive Mutating

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Metaprogramming Runtime Compile-time Additive Mutating Reflection / Parser

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Metaprogramming Runtime Compile-time Additive Mutating Reflection / Parser Source generator / Bytecode generator

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Metaprogramming Runtime Compile-time Additive Mutating Reflection / Parser Source generator / Bytecode generator Source transformer / Bytecode transformer

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Metaprogramming Runtime Compile-time Additive Mutating Reflection / Parser Source generator / Bytecode generator Source transformer / Bytecode transformer

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SomeLibrary.doSomething(User.class);

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SomeLibrary.doSomething(User.class); AnotherLibrary.doSomething(this);

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SomeLibrary.doSomething(User.class); AnotherLibrary.doSomething(this); class AnotherLibrary { static void doSomething(Object instance) { Class> cls = instance.getClass(); // ... } }

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for (Method method : moduleClass.getDeclaredMethods()) { Type returnType = method.getGenericReturnType(); if ((method.getModifiers() & ABSTRACT) != 0) { if (method.getAnnotation(Binds.class) != null) { // ... } else if (method.getAnnotation(BindsOptionalOf.class) != null) { // ... } } else { if ((method.getModifiers() & STATIC) == 0 && instance == null) { // ... } if (method.getAnnotation(Provides.class) != null) { // ... } } }

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for (Method method : moduleClass.getDeclaredMethods()) { Type returnType = method.getGenericReturnType(); if ((method.getModifiers() & ABSTRACT) != 0) { if (method.getAnnotation(Binds.class) != null) { // ... } else if (method.getAnnotation(BindsOptionalOf.class) != null) { // ... } } else { if ((method.getModifiers() & STATIC) == 0 && instance == null) { // ... } if (method.getAnnotation(Provides.class) != null) { // ... } } }

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for (Method method : moduleClass.getDeclaredMethods()) { Type returnType = method.getGenericReturnType(); if ((method.getModifiers() & ABSTRACT) != 0) { if (method.getAnnotation(Binds.class) != null) { // ... } else if (method.getAnnotation(BindsOptionalOf.class) != null) { // ... } } else { if ((method.getModifiers() & STATIC) == 0 && instance == null) { // ... } if (method.getAnnotation(Provides.class) != null) { // ... } } }

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for (Method method : moduleClass.getDeclaredMethods()) { Type returnType = method.getGenericReturnType(); if ((method.getModifiers() & ABSTRACT) != 0) { if (method.getAnnotation(Binds.class) != null) { // ... } else if (method.getAnnotation(BindsOptionalOf.class) != null) { // ... } } else { if ((method.getModifiers() & STATIC) == 0 && instance == null) { // ... } if (method.getAnnotation(Provides.class) != null) { // ... } } }

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for (Method method : moduleClass.getDeclaredMethods()) { Type returnType = method.getGenericReturnType(); if ((method.getModifiers() & ABSTRACT) != 0) { if (method.getAnnotation(Binds.class) != null) { // ... } else if (method.getAnnotation(BindsOptionalOf.class) != null) { // ... } } else { if ((method.getModifiers() & STATIC) == 0 && instance == null) { // ... } if (method.getAnnotation(Provides.class) != null) { // ... } } }

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for (Method method : moduleClass.getDeclaredMethods()) { Type returnType = method.getGenericReturnType(); if ((method.getModifiers() & ABSTRACT) != 0) { if (method.getAnnotation(Binds.class) != null) { // ... } else if (method.getAnnotation(BindsOptionalOf.class) != null) { // ... } } else { if ((method.getModifiers() & STATIC) == 0 && instance == null) { // ... } if (method.getAnnotation(Provides.class) != null) { // ... } } }

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Reflection • Only access to the shape of classes, methods, and fields

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Reflection • Only access to the shape of classes, methods, and fields • No access to content of methods

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Reflection • Only access to the shape of classes, methods, and fields • No access to content of methods • Methods can be invoked, fields can be read/written

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Reflection • Only access to the shape of classes, methods, and fields • No access to content of methods • Methods can be invoked, fields can be read/written • Shape is immutable, no new methods, fields, or types

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Reflection • Only access to the shape of classes, methods, and fields • No access to content of methods • Methods can be invoked, fields can be read/written • Shape is immutable, no new methods, fields, or types • Annotations can be read from method, field, parameters, and types

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Reflection • Only access to the shape of classes, methods, and fields • No access to content of methods • Methods can be invoked, fields can be read/written • Shape is immutable, no new methods, fields, or types • Annotations can be read from method, field, parameters, and types • Relatively slow compared to using methods and fields normally

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public T create(final Class service) { Utils.validateServiceInterface(service); return (T) Proxy.newProxyInstance( service.getClassLoader(), new Class>[] { service }, new InvocationHandler() { @Override public @Nullable Object invoke(Object proxy, Method method, @Nullable Object[] args) throws Throwable { // If the method is from Object then defer to normal invocation. if (method.getDeclaringClass() == Object.class) { return method.invoke(this, args); } return loadServiceMethod(method).invoke(args); } }); }

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public T create(final Class service) { Utils.validateServiceInterface(service); return (T) Proxy.newProxyInstance( service.getClassLoader(), new Class>[] { service }, new InvocationHandler() { @Override public @Nullable Object invoke(Object proxy, Method method, @Nullable Object[] args) throws Throwable { // If the method is from Object then defer to normal invocation. if (method.getDeclaringClass() == Object.class) { return method.invoke(this, args); } return loadServiceMethod(method).invoke(args); } }); }

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public T create(final Class service) { Utils.validateServiceInterface(service); return (T) Proxy.newProxyInstance( service.getClassLoader(), new Class>[] { service }, new InvocationHandler() { @Override public @Nullable Object invoke(Object proxy, Method method, @Nullable Object[] args) throws Throwable { // If the method is from Object then defer to normal invocation. if (method.getDeclaringClass() == Object.class) { return method.invoke(this, args); } return loadServiceMethod(method).invoke(args); } }); }

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public T create(final Class service) { Utils.validateServiceInterface(service); return (T) Proxy.newProxyInstance( service.getClassLoader(), new Class>[] { service }, new InvocationHandler() { @Override public @Nullable Object invoke(Object proxy, Method method, @Nullable Object[] args) throws Throwable { // If the method is from Object then defer to normal invocation. if (method.getDeclaringClass() == Object.class) { return method.invoke(this, args); } return loadServiceMethod(method).invoke(args); } }); }

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public T create(final Class service) { Utils.validateServiceInterface(service); return (T) Proxy.newProxyInstance( service.getClassLoader(), new Class>[] { service }, new InvocationHandler() { @Override public @Nullable Object invoke(Object proxy, Method method, @Nullable Object[] args) throws Throwable { // If the method is from Object then defer to normal invocation. if (method.getDeclaringClass() == Object.class) { return method.invoke(this, args); } return loadServiceMethod(method).invoke(args); } }); }

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public T create(final Class service) { Utils.validateServiceInterface(service); return (T) Proxy.newProxyInstance( service.getClassLoader(), new Class>[] { service }, new InvocationHandler() { @Override public @Nullable Object invoke(Object proxy, Method method, @Nullable Object[] args) throws Throwable { // If the method is from Object then defer to normal invocation. if (method.getDeclaringClass() == Object.class) { return method.invoke(this, args); } return loadServiceMethod(method).invoke(args); } }); }

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Reflection • Only access to the shape of classes, methods, and fields • No access to content of methods • Methods can be invoked, fields can be read/written • Shape is immutable, no new methods, fields, or types • Annotations can be read from method, field, parameters, and types • Relatively slow compared to using methods and fields normally

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Reflection • Only access to the shape of classes, methods, and fields • No access to content of methods • Methods can be invoked, fields can be read/written • Shape is immutable, no new methods, fields, or types • Annotations can be read from method, field, parameters, and types • Relatively slow compared to using methods and fields normally • Can create implementations of interfaces

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Reflection • GOOD: Debug tools and testing where performance is less of a concern

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Reflection • GOOD: Debug tools and testing where performance is less of a concern • GOOD: When dominated by a slower operation like network I/O

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Reflection • GOOD: Debug tools and testing where performance is less of a concern • GOOD: When dominated by a slower operation like network I/O • OKAY: When on critical path and used infrequently

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Reflection • GOOD: Debug tools and testing where performance is less of a concern • GOOD: When dominated by a slower operation like network I/O • OKAY: When on critical path and used infrequently • MEH: When used with R8 or ProGuard

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Reflection • GOOD: Debug tools and testing where performance is less of a concern • GOOD: When dominated by a slower operation like network I/O • OKAY: When on critical path and used infrequently • MEH: When used with R8 or ProGuard • BAD: When on critical path and used heavily

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Metaprogramming Runtime Compile-time Additive Mutating Reflection / Parser Source generator / Bytecode generator Source transformer / Bytecode transformer

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Metaprogramming Runtime Compile-time Additive Mutating Reflection / Parser Source generator / Bytecode generator Source transformer / Bytecode transformer

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SomeLibrary.doSomething(R.raw.stuff);

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SomeLibrary.doSomething(R.raw.stuff); AnotherLibrary.doSomething("foo.txt");

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SomeLibrary.doSomething(R.raw.stuff); AnotherLibrary.doSomething("foo.txt"); Response response = // ... Library.doSomething(response.body().string());

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{"v":"4.8.0","fr":29.9700012207031,"ip":0,"op":61.0000024845809,"w":150,"h":150,"nm":"Name","ddd": 0,"assets":[],"fonts":{"list":[{"origin":0,"fPath":"","fClass":"","fFamily":"Comic Neue","fWeight":"","fStyle":"Regular","fName":"ComicNeue","ascent":69.6990966796875}]},"layers":[{"ddd": 0,"ind":1,"ty":5,"nm":"NAME","ks":{"o":{"a":0,"k":100},"r":{"a":0,"k":0},"p":{"a":1,"k":[{"i":{"x": 0.833,"y":0.833},"o":{"x":0.167,"y":0.167},"n":"0p833_0p833_0p167_0p167","t":0,"s":[10.5,15,0],"e": [10.5,147,0],"to":[0,22,0],"ti":[0,0,0]},{"i":{"x":0.833,"y":0.833},"o":{"x":0.167,"y": 0.167},"n":"0p833_0p833_0p167_0p167","t":15,"s":[10.5,147,0],"e":[10.5,15,0],"to":[0,0,0],"ti":[0,22,0]}, {"t":30.0000012219251}]},"a":{"a":0,"k":[0,0,0]},"s":{"a":1,"k":[{"i":{"x":[0.833,0.833,0.833],"y": [0.833,0.833,0.833]},"o":{"x":[0.167,0.167,0.167],"y":[0.167,0.167,0.167]},"n": ["0p833_0p833_0p167_0p167","0p833_0p833_0p167_0p167","0p833_0p833_0p167_0p167"],"t":0,"s": [100,100,100],"e":[196,196,100]},{"i":{"x":[0.833,0.833,0.833],"y":[0.833,0.833,0.833]},"o":{"x": [0.167,0.167,0.167],"y":[0.167,0.167,0.167]},"n": ["0p833_0p833_0p167_0p167","0p833_0p833_0p167_0p167","0p833_0p833_0p167_0p167"],"t":15,"s": [196,196,100],"e":[100,100,100]},{"t":30.0000012219251}]}},"ao":0,"t":{"d":{"k":[{"s":{"s": 14,"f":"ComicNeue","t":"NAME","j":0,"tr":0,"lh":16.8,"ls":0,"fc":[0.92,0,0]},"t":0}]},"p":{},"m":{"g": 1,"a":{"a":0,"k":[0,0]}},"a":[{"s":{"t":0,"xe":{"a":0,"k":0},"ne":{"a":0,"k":0},"a":{"a":0,"k":100},"b": 1,"rn":0,"sh":1,"r":1},"a":{"fc":{"a":1,"k":[{"i":{"x":[0.833],"y":[0.833]},"o":{"x":[0.167],"y": [0.167]},"n":["0p833_0p833_0p167_0p167"],"t":0,"s":[1,0,0,1],"e":[0,1,0,1]},{"i":{"x":[0.833],"y": [0.833]},"o":{"x":[0.167],"y":[0.167]},"n":["0p833_0p833_0p167_0p167"],"t":15,"s":[0,1,0,1],"e": [0,0,1,1]},{"i":{"x":[0.833],"y":[0.833]},"o":{"x":[0.167],"y":[0.167]},"n": ["0p833_0p833_0p167_0p167"],"t":30,"s":[0,0,1,1],"e":[0,1,0,1]},{"i":{"x":[0.833],"y":[0.833]},"o":{"x": [0.167],"y":[0.167]},"n":["0p833_0p833_0p167_0p167"],"t":45,"s":[0,1,0,1],"e":[1,0,0,1]},{"t": 60.0000024438501}]},"t":{"a":1,"k":[{"i":{"x":[0.833],"y":[0.833]},"o":{"x":[0.167],"y":[0.167]},"n": ["0p833_0p833_0p167_0p167"],"t":30,"s":[0],"e":[20]},{"i":{"x":[0.833],"y":[0.833]},"o":{"x":[0.167],"y": [0.167]},"n":["0p833_0p833_0p167_0p167"],"t":45,"s":[20],"e":[0]},{"t":60.0000024438501}]}}}]},"ip": 0,"op":61.0000024845809,"st":0,"bm":0,"sr":1}]}

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No content

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• Use any format / schema / language as input Parsing

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• Use any format / schema / language as input • Be mindful of forward/backward compatibility with inputs Parsing

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• Use any format / schema / language as input • Be mindful of forward/backward compatibility with inputs • Invoke existing framework APIs or ones from a library Parsing

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Parsing • GOOD: Re-use output formats from existing tools

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Parsing • GOOD: Re-use output formats from existing tools • GOOD: Behavior can be loaded from external resource like a server

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Parsing • GOOD: Re-use output formats from existing tools • GOOD: Behavior can be loaded from external resource like a server • OKAY: When on critical path and used infrequently

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Parsing • GOOD: Re-use output formats from existing tools • GOOD: Behavior can be loaded from external resource like a server • OKAY: When on critical path and used infrequently • BAD: When on critical path and used heavily

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Metaprogramming Runtime Compile-time Additive Mutating Reflection / Parser Source generator / Bytecode generator Source transformer / Bytecode transformer

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Metaprogramming Runtime Compile-time Additive Mutating Reflection / Parser Source generator / Bytecode generator Source transformer / Bytecode transformer

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message Person { required uint64 id = 1; required string name = 2; optional string email = 3; }

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message Person { required uint64 id = 1; required string name = 2; optional string email = 3; } class Person { long getId() { .. } String getName() { .. } String getEmail() { .. } class Builder { Builder setId(long id) { .. } Builder setName(String name) { .. } Builder setEmail(String email) { .. } Person build() { .. } } }

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@AutoValue abstract class Person { static Person from(long id, String name, String email) { return new AutoValue_Person(id, name, email); } abstract long id(); abstract String name(); abstract String email(); }

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@AutoValue abstract class Person { static Person from(long id, String name, String email) { return new AutoValue_Person(id, name, email); } abstract long id(); abstract String name(); abstract String email(); }

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@AutoValue abstract class Person { static Person from(long id, String name, String email) { return new AutoValue_Person(id, name, email); } abstract long id(); abstract String name(); abstract String email(); }

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@AutoValue abstract class Person { static Person from(long id, String name, String email) { return new AutoValue_Person(id, name, email); } abstract long id(); abstract String name(); abstract String email(); }

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@AutoValue abstract class Person { static Person from(long id, String name, String email) { return new AutoValue_Person(id, name, email); } abstract long id(); abstract String name(); abstract String email(); } final class AutoValue_Person extends Person { AutoValue_Person(long id, String name, String email) { .. } @Override abstract long id() { .. } @Override abstract String name() { .. } @Override abstract String email() { .. } // equals(), hashCode(), toString()... }

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• Only access to the shape of classes, methods, and fields Source Generator (Annotation Processor)

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• Only access to the shape of classes, methods, and fields • No access to content of methods Source Generator (Annotation Processor)

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• Only access to the shape of classes, methods, and fields • No access to content of methods • Shape of existing code is immutable, no new methods, fields, or types Source Generator (Annotation Processor)

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• Only access to the shape of classes, methods, and fields • No access to content of methods • Shape of existing code is immutable, no new methods, fields, or types • Annotations can be read from method, field, parameters, and types Source Generator (Annotation Processor)

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• Only access to the shape of classes, methods, and fields • No access to content of methods • Shape of existing code is immutable, no new methods, fields, or types • Annotations can be read from method, field, parameters, and types • Can generate any kind of type or a Java resource Source Generator (Annotation Processor)

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• Only access to the shape of classes, methods, and fields • No access to content of methods • Shape of existing code is immutable, no new methods, fields, or types • Annotations can be read from method, field, parameters, and types • Can generate any kind of type or a Java resource • Avoid leaking generated code into API, treat as implementation detail Source Generator (Annotation Processor)

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• Only access to the shape of classes, methods, and fields • No access to content of methods • Shape of existing code is immutable, no new methods, fields, or types • Annotations can be read from method, field, parameters, and types • Can generate any kind of type or a Java resource • Avoid leaking generated code into API, treat as implementation detail • Use JavaPoet, KotlinPoet, auto-common, and/or compile-testing to build Source Generator (Annotation Processor)

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• Generated source code can be public API and should feel like a library Source Generator (Other)

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• Generated source code can be public API and should feel like a library • You can generate inputs to other tools like ProGuard rules or drawable XML Source Generator (Other)

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• Generated source code can be public API and should feel like a library • You can generate inputs to other tools like ProGuard rules or drawable XML • Use JavaPoet and KotlinPoet for source generation Source Generator (Other)

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• GOOD: Same performance and capability as hand-written code Source Generator

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• GOOD: Same performance and capability as hand-written code • GOOD: Relatively easy to create and change Source Generator

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• GOOD: Same performance and capability as hand-written code • GOOD: Relatively easy to create and change • GOOD: Works extremely well with R8 and ProGuard Source Generator

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• GOOD: Same performance and capability as hand-written code • GOOD: Relatively easy to create and change • GOOD: Works extremely well with R8 and ProGuard • OKAY: Can contribute a lot of methods, fields, and allocations Source Generator

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• GOOD: Same performance and capability as hand-written code • GOOD: Relatively easy to create and change • GOOD: Works extremely well with R8 and ProGuard • OKAY: Can contribute a lot of methods, fields, and allocations • MEH: Referencing generated code from annotation processors Source Generator

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• GOOD: Same performance and capability as hand-written code • GOOD: Relatively easy to create and change • GOOD: Works extremely well with R8 and ProGuard • OKAY: Can contribute a lot of methods, fields, and allocations • MEH: Referencing generated code from annotation processors • MEH: Build performance impact requires care Source Generator

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Metaprogramming Runtime Compile-time Additive Mutating Reflection / Parser Source generator / Bytecode generator Source transformer / Bytecode transformer

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Metaprogramming Runtime Compile-time Additive Mutating Reflection / Parser Source generator / Bytecode generator Source transformer / Bytecode transformer

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// search_item.xml

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// search_item.xml

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// search_item.xml final class R { static final class id { static final int class_name = 0x7f0000001; static final int more_options = 0x7f000002; static final int package_name = 0x7f000003; } static final class layout { static final int search_item = 0x7f000004; } }

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// search_item.xml $ find build -name 'R.*' build/intermediates/r_class_jar/release/generateReleaseRFile/R.jar build/intermediates/r_class_jar/debug/generateDebugRFile/R.jar

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// search_item.xml $ find build -name 'R.*' build/intermediates/r_class_jar/release/generateReleaseRFile/R.jar build/intermediates/r_class_jar/debug/generateDebugRFile/R.jar $ javap -cp build/.../generateReleaseRFile/R.jar 'com.example.R$layout' public final class com.jakewharton.sdksearch.search.ui.R$layout { public static final int class_name; public static final int more_options; public static final int package_name; }

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Bytecode Generator • Same basic guidelines as source generation

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Bytecode Generator • Same basic guidelines as source generation • Use ASM or ByteBuddy, or some kind of IR

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Bytecode Generator • GOOD: Same or better performance and capability as hand-written code

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Bytecode Generator • GOOD: Same or better performance and capability as hand-written code • GOOD: Works extremely well with R8 and ProGuard

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Bytecode Generator • GOOD: Same or better performance and capability as hand-written code • GOOD: Works extremely well with R8 and ProGuard • GOOD: Avoids the need to run Java and Kotlin compiler

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Bytecode Generator • GOOD: Same or better performance and capability as hand-written code • GOOD: Works extremely well with R8 and ProGuard • GOOD: Avoids the need to run Java and Kotlin compiler • MEH: Somewhat hard to write and maintain

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Bytecode Generator • GOOD: Same or better performance and capability as hand-written code • GOOD: Works extremely well with R8 and ProGuard • GOOD: Avoids the need to run Java and Kotlin compiler • MEH: Somewhat hard to write and maintain • BAD: No source code to step through while debugging

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Metaprogramming Runtime Compile-time Additive Mutating Reflection / Parser Source generator / Bytecode generator Source transformer / Bytecode transformer

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Metaprogramming Runtime Compile-time Additive Mutating Reflection / Parser Source generator / Bytecode generator Source transformer / Bytecode transformer

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class TimedRunnable implements Comparable { final long execTime; @Override public int compareTo(TimedRunnable that) { return Long.compare(execTime, that.execTime); } }

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class TimedRunnable implements Comparable { final long execTime; @Override public int compareTo(TimedRunnable that) { return Long.compare(execTime, that.execTime); } }

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class TimedRunnable implements Comparable { final long execTime; @Override public int compareTo(TimedRunnable that) { return Long.compare(execTime, that.execTime); } } java/lang/Long.compare --> io/reactivex/internal/java/lang/Long.compare

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class TimedRunnable implements Comparable { final long execTime; @Override public int compareTo(TimedRunnable that) { return Long.compare(execTime, that.execTime); } } java/lang/Long.compare --> io/reactivex/internal/java/lang/Long.compare class TimedRunnable implements Comparable { final long execTime; @Override public int compareTo(TimedRunnable that) { return io.reactivex.internal.java.lang.Long.compare( execTime, that.execTime); } }

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Source Transformer • Unlike annotation processing, you have access to method body content

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Source Transformer • Unlike annotation processing, you have access to method body content • Free to change, update, and delete any types, method, fields, and code

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Source Transformer • Unlike annotation processing, you have access to method body content • Free to change, update, and delete any types, method, fields, and code • Use Spoon for complicated transformations, regex for simple ones

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Source Transformer • GOOD: Can be as simple or complex as needed

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Source Transformer • GOOD: Can be as simple or complex as needed • GOOD: Easy to get started and experiment with

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Source Transformer • GOOD: Can be as simple or complex as needed • GOOD: Easy to get started and experiment with • MEH: Limited applicability

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Source Transformer • GOOD: Can be as simple or complex as needed • GOOD: Easy to get started and experiment with • MEH: Limited applicability • BAD: Transformations are brittle and prone to breakage

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Metaprogramming Runtime Compile-time Additive Mutating Reflection / Parser Source generator / Bytecode generator Source transformer / Bytecode transformer

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Metaprogramming Runtime Compile-time Additive Mutating Reflection / Parser Source generator / Bytecode generator Source transformer / Bytecode transformer

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$ javap -c build/classes/main/io/reactivex/internal/schedulers/TrampolineScheduler\$TimedRunnable.class Compiled from "TrampolineScheduler.java" final class io.reactivex.internal.schedulers.TrampolineScheduler$TimedRunnable implements java.lang.Comparable { final java.lang.Runnable run; final long execTime; public int compareTo(io.reactivex.internal.schedulers.TrampolineScheduler$TimedRunnable); Code: 0: aload_0 1: getfield #5 // Field execTime:J 4: aload_1 5: getfield #5 // Field execTime:J 8: invokestatic #7 // Method java/lang/Long.compare:(JJ)I 11: ireturn }

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$ javap -c build/classes/main/io/reactivex/internal/schedulers/TrampolineScheduler\$TimedRunnable.class Compiled from "TrampolineScheduler.java" final class io.reactivex.internal.schedulers.TrampolineScheduler$TimedRunnable implements java.lang.Comparable { final java.lang.Runnable run; final long execTime; public int compareTo(io.reactivex.internal.schedulers.TrampolineScheduler$TimedRunnable); Code: 0: aload_0 1: getfield #5 // Field execTime:J 4: aload_1 5: getfield #5 // Field execTime:J 8: invokestatic #7 // Method java/lang/Long.compare:(JJ)I 11: ireturn }

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final class BackportingMethodCallRemapper extends ClassVisitor { BackportingMethodCallRemapper(ClassVisitor cv) { super(ASM5, cv); } @Override public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions) { MethodVisitor mv = super.visitMethod(access, name, desc, signature, exceptions); if (mv == null) { return null; } return new MethodVisitor(ASM5, mv) { @Override public void visitMethodInsn(int opcode, String owner, String name, String desc, boolean itf) { if ("java/lang/Long".equals(owner) && "compare".equals(name)) { owner = "io/reactivex/internal/java/lang/Long"; } super.visitMethodInsn(opcode, owner, name, desc, itf); } }; } }

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final class BackportingMethodCallRemapper extends ClassVisitor { BackportingMethodCallRemapper(ClassVisitor cv) { super(ASM5, cv); } @Override public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions) { MethodVisitor mv = super.visitMethod(access, name, desc, signature, exceptions); if (mv == null) { return null; } return new MethodVisitor(ASM5, mv) { @Override public void visitMethodInsn(int opcode, String owner, String name, String desc, boolean itf) { if ("java/lang/Long".equals(owner) && "compare".equals(name)) { owner = "io/reactivex/internal/java/lang/Long"; } super.visitMethodInsn(opcode, owner, name, desc, itf); } }; } }

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$ javap -c build/classes/main/io/reactivex/internal/schedulers/TrampolineScheduler\$TimedRunnable.class Compiled from "TrampolineScheduler.java" final class io.reactivex.internal.schedulers.TrampolineScheduler$TimedRunnable implements java.lang.Comparable { final java.lang.Runnable run; final long execTime; public int compareTo(io.reactivex.internal.schedulers.TrampolineScheduler$TimedRunnable); Code: 0: aload_0 1: getfield #5 // Field execTime:J 4: aload_1 5: getfield #5 // Field execTime:J 8: invokestatic #7 // Method io/reactivex/internal/java/lang/Long.compare:(JJ)I 11: ireturn }

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$ javap -c build/classes/main/io/reactivex/internal/schedulers/TrampolineScheduler\$TimedRunnable.class Compiled from "TrampolineScheduler.java" final class io.reactivex.internal.schedulers.TrampolineScheduler$TimedRunnable implements java.lang.Comparable { final java.lang.Runnable run; final long execTime; public int compareTo(io.reactivex.internal.schedulers.TrampolineScheduler$TimedRunnable); Code: 0: aload_0 1: getfield #5 // Field execTime:J 4: aload_1 5: getfield #5 // Field execTime:J 8: invokestatic #7 // Method io/reactivex/internal/java/lang/Long.compare:(JJ)I 11: ireturn }

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public static void main(String... args) { sayHi(s -> System.out.println(s)); }

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public static void main(String... args) { sayHi(s -> System.out.println(s)); } BootstrapMethods: 0: #27 invokestatic java/lang/invoke/LambdaMetafactory.metafactory:( Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String; Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodType; Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/ MethodType;) Ljava/lang/invoke/CallSite; Method arguments: #28 (Ljava/lang/String;)V #29 invokestatic Java8.lambda$main$0:(Ljava/lang/String;)V #28 (Ljava/lang/String;)V

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public static void main(String... args) { sayHi(s -> System.out.println(s)); } [0002bc] Java8.main:([Ljava/lang/String;)V 0000: sget-object v1, Ljava/lang/System;.out:Ljava/io/PrintStream; 0003: new-instance v0, L-$$Lambda$1Osqr2Z9OSwjseX_0FMQJcCG_uM; 0004: invoke-direct {v0, v1}, L-$$Lambda$1Osqr2Z9OSwjseX_0FMQJcCG_uM;.: (Ljava/io/PrintStream;)V 0008: invoke-static {v0}, LJava8;.sayHi:(LJava8$Logger;)V

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Bytecode Transformer • Free to change, update, and delete any types, method, fields, and code

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Bytecode Transformer • Free to change, update, and delete any types, method, fields, and code • Create constructs which cannot be represented in source

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Bytecode Transformer • Free to change, update, and delete any types, method, fields, and code • Create constructs which cannot be represented in source • Use ASM or ByteBuddy, or some kind of IR

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Bytecode Transformer • GOOD: Unlimited power to create, modify, and delete anything as desired

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Bytecode Transformer • GOOD: Unlimited power to create, modify, and delete anything as desired • OKAY: Build system integration not always easy

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Bytecode Transformer • GOOD: Unlimited power to create, modify, and delete anything as desired • OKAY: Build system integration not always easy • OKAY: Can affect debugging and stacktraces in non-obvious ways

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Bytecode Transformer • GOOD: Unlimited power to create, modify, and delete anything as desired • OKAY: Build system integration not always easy • OKAY: Can affect debugging and stacktraces in non-obvious ways • MEH: Requires a lot of machinery and knowledge of bytecode

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Metaprogramming Runtime Compile-time Additive Mutating Reflection / Parser Source generator / Bytecode generator Source transformer / Bytecode transformer

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Metaprogramming Runtime Compile-time Additive Mutating Reflection / Parser Source generator / Bytecode generator Source transformer / Bytecode transformer

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Network Requests

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GET /users HTTP/1.1 [{id:1,name:"Jake"}]

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[{id:1,name:"Jake"}] GET /users HTTP/1.1

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[{id:1,name:"Jake"}] GET /users HTTP/1.1

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interface GitHubService { suspend fun users(): List }X data class User( val id: Long, val login: String )Y

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interface GitHubService { @GET("/users") suspend fun users(): List }X data class User( val id: Long, val login: String )Y

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interface GitHubService { @GET("/users") suspend fun users(): List }X @JsonClass data class User( val id: Long, val login: String )Y

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interface GitHubService { @GET("/users") suspend fun users(): List }X @JsonClass data class User( val id: Long, val login: String )Y

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interface GitHubService { @GET("/users") suspend fun users(): List }X @JsonClass data class User( val id: Long, val login: String )Y

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GET /users HTTP/1.1 [{id:1,name:"Jake"}]

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GET /users HTTP/1.1 [{id:1,name:"Jake"}]

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interface GitHubService { @GET("/users") suspend fun users(): List }X @JsonClass data class User( val id: Long, val login: String )Y

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interface GitHubService { @GET("/users") suspend fun users(): List }X @JsonClass data class User( val id: Long, val login: String )Y

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GET /users HTTP/1.1 [{id:1,name:"Jake"}] interface GitHubService { @GET("/users") suspend fun users(): List }X @JsonClass data class User( val id: Long, val login: String )Y

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interface GitHubService {A @GET("/users") suspend fun users(): List }X

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class GitHubService(val client: OkHttpClient) {A suspend fun users(): List { // ... }B }X i n t e r f a c e @GET("/users")

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Android Layouts

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// search_item.xml

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class SearchItemActivity extends Activity { private TextView packageNameView; private TextView classNameView; private ImageButton moreOptionsView; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.search_item); packageNameView = findViewById(R.id.package_name); classNameView = findViewById(R.id.class_name); moreOptionsView = findViewById(R.id.more_options); }B void later() { packageName.setText("com.example"); className.setText("ExampleClass"); moreOptions.setImageResource(R.drawable.view_source); }B }A

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private private private packageNameView = findViewById( ); classNameView = findViewById( ); moreOptionsView = findViewById( ); class SearchItemActivity extends Activity { @BindView(R.id.package_name) TextView packageNameView; @BindView(R.id.class_name) TextView classNameView; @BindView(R.id.more_options) ImageButton moreOptionsView; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.search_item); ButterKnife.bind(this); }B void later() { packageName.setText("com.example"); className.setText("ExampleClass"); moreOptions.setImageResource(R.drawable.view_source); }B }A

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class SearchItemActivity : Activity { @Override fun onCreate(savedInstanceState: Bundle) { super.onCreate(savedInstanceState) setContentView(R.layout.search_item) }B fun later() { packageName.text = "com.example" className.text = "ExampleClass" moreOptions.setImageResource(R.drawable.view_source) }B }A e x t e n d s @BindView(R.id.package_name) TextView packageNameView; @BindView(R.id.class_name) TextView classNameView; @BindView(R.id.more_options) ImageButton moreOptionsView; protected void ButterKnife.bind(this); void setText( ); setText( );

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// search_item.xml

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// search_item.xml 1. Layout file name

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// search_item.xml 1. Layout file name 2. Root view type

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// search_item.xml 1. Layout file name 2. Root view type 3. Type of each view with ID

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// search_item.xml 1. Layout file name 2. Root view type 3. Type of each view with ID 4. Which IDs are contained
 inside each layout

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// search_item.xml 1. Layout file name 2. Root view type 3. Type of each view with ID 4. Which IDs are contained
 inside each layout 5. Whether an ID is present in
 every layout configuration

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class SearchItemActivity extends Activity { private TextView packageNameView; private TextView classNameView; private ImageButton moreOptionsView; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.search_item); packageNameView = findViewById(R.id.package_name); classNameView = findViewById(R.id.class_name); moreOptionsView = findViewById(R.id.more_options); }B void later() { packageName.setText("com.example"); className.setText("ExampleClass"); moreOptions.setImageResource(R.drawable.view_source); } }A 1. Layout file name 2. Root view type 3. Type of each view with ID 4. Which IDs are contained
 inside each layout 5. Whether an ID is present in
 every layout configuration

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class SearchItemActivity extends Activity { private TextView packageNameView; private TextView classNameView; private ImageButton moreOptionsView; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.search_item); packageNameView = findViewById(R.id.package_name); classNameView = findViewById(R.id.class_name); moreOptionsView = findViewById(R.id.more_options); }B void later() { packageName.setText("com.example"); className.setText("ExampleClass"); moreOptions.setImageResource(R.drawable.view_source); } }A 1. Layout file name 2. Root view type 3. Type of each view with ID 4. Which IDs are contained
 inside each layout 5. Whether an ID is present in
 every layout configuration

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class SearchItemActivity extends Activity { private TextView packageNameView; private TextView classNameView; private ImageButton moreOptionsView; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.search_item); packageNameView = findViewById(R.id.package_name); classNameView = findViewById(R.id.class_name); moreOptionsView = findViewById(R.id.more_options); }B void later() { packageName.setText("com.example"); className.setText("ExampleClass"); moreOptions.setImageResource(R.drawable.view_source); } }A 1. Layout file name 3. Type of each view with ID 4. Which IDs are contained
 inside each layout 5. Whether an ID is present in
 every layout configuration 2. Root view type

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class SearchItemActivity extends Activity { private TextView packageNameView; private TextView classNameView; private ImageButton moreOptionsView; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.search_item); packageNameView = findViewById(R.id.package_name); classNameView = findViewById(R.id.class_name); moreOptionsView = findViewById(R.id.more_options); }B void later() { packageName.setText("com.example"); className.setText("ExampleClass"); moreOptions.setImageResource(R.drawable.view_source); } }A 1. Layout file name 4. Which IDs are contained
 inside each layout 5. Whether an ID is present in
 every layout configuration 2. Root view type 3. Type of each view with ID

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class SearchItemActivity extends Activity { private TextView packageNameView; private TextView classNameView; private ImageButton moreOptionsView; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.search_item); packageNameView = findViewById(R.id.package_name); classNameView = findViewById(R.id.class_name); moreOptionsView = findViewById(R.id.more_options); }B void later() { packageName.setText("com.example"); className.setText("ExampleClass"); moreOptions.setImageResource(R.drawable.view_source); } }A 1. Layout file name 5. Whether an ID is present in
 every layout configuration 2. Root view type 3. Type of each view with ID 4. Which IDs are contained
 inside each layout

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class SearchItemActivity extends Activity { private TextView packageNameView; private TextView classNameView; private ImageButton moreOptionsView; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.search_item); packageNameView = findViewById(R.id.package_name); classNameView = findViewById(R.id.class_name); moreOptionsView = findViewById(R.id.more_options); }B void later() { packageName.setText("com.example"); className.setText("ExampleClass"); moreOptions.setImageResource(R.drawable.view_source); } }A 1. Layout file name 2. Root view type 3. Type of each view with ID 4. Which IDs are contained
 inside each layout 5. Whether an ID is present in
 every layout configuration

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class SearchItemActivity extends Activity { @BindView(R.id.package_name) TextView packageNameView; @BindView(R.id.class_name) TextView classNameView; @BindView(R.id.more_options) ImageButton moreOptionsView; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.search_item); ButterKnife.bind(this); }B void later() { packageName.setText("com.example"); className.setText("ExampleClass"); moreOptions.setImageResource(R.drawable.view_source); } }A 1. Layout file name 2. Root view type 3. Type of each view with ID 4. Which IDs are contained
 inside each layout 5. Whether an ID is present in
 every layout configuration

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class SearchItemActivity extends Activity { @BindView(R.id.package_name) TextView packageNameView; @BindView(R.id.class_name) TextView classNameView; @BindView(R.id.more_options) ImageButton moreOptionsView; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.search_item); ButterKnife.bind(this); }B void later() { packageName.setText("com.example"); className.setText("ExampleClass"); moreOptions.setImageResource(R.drawable.view_source); } }A 1. Layout file name 2. Root view type 3. Type of each view with ID 4. Which IDs are contained
 inside each layout 5. Whether an ID is present in
 every layout configuration

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class SearchItemActivity extends Activity { @BindView(R.id.package_name) TextView packageNameView; @BindView(R.id.class_name) TextView classNameView; @BindView(R.id.more_options) ImageButton moreOptionsView; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.search_item); ButterKnife.bind(this); }B void later() { packageName.setText("com.example"); className.setText("ExampleClass"); moreOptions.setImageResource(R.drawable.view_source); } }A 1. Layout file name 2. Root view type 3. Type of each view with ID 4. Which IDs are contained
 inside each layout 5. Whether an ID is present in
 every layout configuration

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class SearchItemActivity extends Activity { @BindView(R.id.package_name) TextView packageNameView; @BindView(R.id.class_name) TextView classNameView; @BindView(R.id.more_options) ImageButton moreOptionsView; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.search_item); ButterKnife.bind(this); }B void later() { packageName.setText("com.example"); className.setText("ExampleClass"); moreOptions.setImageResource(R.drawable.view_source); } }A 1. Layout file name 2. Root view type 3. Type of each view with ID 4. Which IDs are contained
 inside each layout 5. Whether an ID is present in
 every layout configuration

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class SearchItemActivity extends Activity { @BindView(R.id.package_name) TextView packageNameView; @BindView(R.id.class_name) TextView classNameView; @BindView(R.id.more_options) ImageButton moreOptionsView; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.search_item); ButterKnife.bind(this); }B void later() { packageName.setText("com.example"); className.setText("ExampleClass"); moreOptions.setImageResource(R.drawable.view_source); } }A 1. Layout file name 2. Root view type 3. Type of each view with ID 4. Which IDs are contained
 inside each layout 5. Whether an ID is present in
 every layout configuration

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class SearchItemActivity extends Activity { @BindView(R.id.package_name) TextView packageNameView; @BindView(R.id.class_name) TextView classNameView; @BindView(R.id.more_options) ImageButton moreOptionsView; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.search_item); ButterKnife.bind(this); }B void later() { packageName.setText("com.example"); className.setText("ExampleClass"); moreOptions.setImageResource(R.drawable.view_source); } }A 1. Layout file name 2. Root view type 3. Type of each view with ID 4. Which IDs are contained
 inside each layout 5. Whether an ID is present in
 every layout configuration

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class SearchItemActivity : Activity { @Override fun onCreate(savedInstanceState: Bundle) { super.onCreate(savedInstanceState) setContentView(R.layout.search_item) }B fun later() { packageName.text = "com.example" className.text = "ExampleClass" moreOptions.setImageResource(R.drawable.view_source) } }A 1. Layout file name 2. Root view type 3. Type of each view with ID 4. Which IDs are contained
 inside each layout 5. Whether an ID is present in
 every layout configuration

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class SearchItemActivity : Activity { @Override fun onCreate(savedInstanceState: Bundle) { super.onCreate(savedInstanceState) setContentView(R.layout.search_item) }B fun later() { packageName.text = "com.example" className.text = "ExampleClass" moreOptions.setImageResource(R.drawable.view_source) } }A 1. Layout file name 2. Root view type 3. Type of each view with ID 4. Which IDs are contained
 inside each layout 5. Whether an ID is present in
 every layout configuration

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class SearchItemActivity : Activity { @Override fun onCreate(savedInstanceState: Bundle) { super.onCreate(savedInstanceState) setContentView(R.layout.search_item) }B fun later() { packageName.text = "com.example" className.text = "ExampleClass" moreOptions.setImageResource(R.drawable.view_source) } }A 1. Layout file name 2. Root view type 3. Type of each view with ID 4. Which IDs are contained
 inside each layout 5. Whether an ID is present in
 every layout configuration

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class SearchItemActivity : Activity { @Override fun onCreate(savedInstanceState: Bundle) { super.onCreate(savedInstanceState) setContentView(R.layout.search_item) }B fun later() { packageName.text = "com.example" className.text = "ExampleClass" moreOptions.setImageResource(R.drawable.view_source) } }A 1. Layout file name 2. Root view type 3. Type of each view with ID 4. Which IDs are contained
 inside each layout 5. Whether an ID is present in
 every layout configuration

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class SearchItemActivity : Activity { @Override fun onCreate(savedInstanceState: Bundle) { super.onCreate(savedInstanceState) setContentView(R.layout.search_item) }B fun later() { packageName.text = "com.example" className.text = "ExampleClass" moreOptions.setImageResource(R.drawable.view_source) } }A 1. Layout file name 2. Root view type 3. Type of each view with ID 4. Which IDs are contained
 inside each layout 5. Whether an ID is present in
 every layout configuration 6. Kotlin-only

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class SearchItemActivity extends Activity { private SearchItemBinding layout; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); layout = setContentView(this, R.layout.search_item); }B void later() { layout.packageName.setText("com.example"); layout.className.setText("ExampleClass"); layout.moreOptions.setImageResource(R.drawable.view_source); } }A 1. Layout file name 3. Type of each view with ID 4. Which IDs are contained
 inside each layout 5. Whether an ID is present in
 every layout configuration 2. Root view type

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class SearchItemActivity extends Activity { private SearchItemBinding layout; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); layout = setContentView(this, R.layout.search_item); }B void later() { layout.packageName.setText("com.example"); layout.className.setText("ExampleClass"); layout.moreOptions.setImageResource(R.drawable.view_source); } }A 1. Layout file name 2. Root view type 3. Type of each view with ID 4. Which IDs are contained
 inside each layout 5. Whether an ID is present in
 every layout configuration

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// search_item.xml

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// search_item.xml

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// search_item.xml Android Gradle plugin

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// search_item.xml Android Gradle plugin class SearchItemBinding { public final TextView packageName; public final TextView className; public final ImageButton moreOptions; }A

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// search_item.xml Android Gradle plugin @Binding class SearchItemBinding { public final TextView packageName; public final TextView className; public final ImageButton moreOptions; }A

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// search_item.xml Android Gradle plugin annotationProcessor 'androidx.databinding:databinding-compiler:3.4.0' @Binding class SearchItemBinding { public final TextView packageName; public final TextView className; public final ImageButton moreOptions; }A

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// search_item.xml Android Gradle plugin Java compiler annotationProcessor 'androidx.databinding:databinding-compiler:3.4.0' @Binding class SearchItemBinding { public final TextView packageName; public final TextView className; public final ImageButton moreOptions; }A

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// search_item.xml Android Gradle plugin Java compiler annotationProcessor 'androidx.databinding:databinding-compiler:3.4.0' @Binding class SearchItemBinding { public final TextView packageName; public final TextView className; public final ImageButton moreOptions; }A class SearchItemBindingImpl extends SearchItemBinding { // ... }A

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// search_item.xml Android Gradle plugin Java compiler annotationProcessor 'androidx.databinding:databinding-compiler:3.4.0' @Binding class SearchItemBinding { public final TextView packageName; public final TextView className; public final ImageButton moreOptions; }A class SearchItemBindingImpl extends SearchItemBinding { // ... }A

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// search_item.xml Android Gradle plugin Java compiler annotationProcessor 'androidx.databinding:databinding-compiler:3.4.0' @Binding class SearchItemBinding { public final TextView packageName; public final TextView className; public final ImageButton moreOptions; }A class SearchItemBindingImpl extends SearchItemBinding { // ... }A

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// search_item.xml Android Gradle plugin Java compiler annotationProcessor 'androidx.databinding:databinding-compiler:3.4.0' @Binding class SearchItemBinding { public final TextView packageName; public final TextView className; public final ImageButton moreOptions; }A class SearchItemBindingImpl extends SearchItemBinding { // ... }A

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class SearchItemActivity extends Activity { private SearchItemBinding layout; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); layout = SearchItemBinding.inflate(this); setContentView(layout); }B void later() { layout.packageName.setText("com.example"); layout.className.setText("ExampleClass"); layout.moreOptions.setImageResource(R.drawable.view_source); } }A 1. Layout file name 2. Root view type 3. Type of each view with ID 4. Which IDs are contained
 inside each layout 5. Whether an ID is present in
 every layout configuration

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class SearchItemActivity extends Activity { private SearchItemBinding layout; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); layout = SearchItemBinding.inflate(this); setContentView(layout); }B void later() { layout.packageName.setText("com.example"); layout.className.setText("ExampleClass"); layout.moreOptions.setImageResource(R.drawable.view_source); } }A (HINT)

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Database Queries

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CREATE TABLE user( id INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT NOT NULL, email TEXT NOT NULL ); SELECT email FROM user WHERE name LIKE 'Jake %'

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@Table("user") class User { @PrimaryKey @AutoIncrement long id; @NotNull String name; @NotNull String email; }A Database db = Database.create(context, User.class, ..); List jakes = db.from(User.class) .where("name", like("Jake %")) .select("email") .toList(String.class);

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Table @A Increment Database db = Database.create(context, User.class, ..); List jakes = db.from(User.class) .where("name", like("Jake %")) .select("email") .toList(String.class); @Entity(tableName = "user") class User { @PrimaryKey(autoGenerate = true) long id; @NotNull String name; @NotNull String email; }A @Dao interface UserDao { @Query("SELECT email FROM user WHERE name LIKE 'JAKE %'") List jakes(); }H

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@Entity(tableName = "user") class User { @PrimaryKey(autoGenerate = true) long id; @NotNull String name; @NotNull String email; }A @Dao interface UserDao { @Query("SELECT email FROM user WHERE name LIKE 'JAKE %'") List jakes(); }H

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@Entity(tableName = "user") class User { @PrimaryKey(autoGenerate = true) long id; @NotNull String name; @NotNull String email; }A @Dao interface UserDao { @Query("SELECT name, email FROM user WHERE name LIKE 'JAKE %'") List??> jakes(); }H S t r i n g User

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@Entity(tableName = "user") class User { @PrimaryKey(autoGenerate = true) long id; @NotNullA String name; @NotNullB String email; }A @Dao interface UserDao { @Query("SELECT * FROM user WHERE name LIKE 'JAKE %'") List jakes(); }H

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@Entity(tableName = "user") class User { @PrimaryKey(autoGenerate = true) long id; @NotNullAString name; @NotNullBString email; @Nullable LocalDate birthday; @NonNull LocalDate created; boolean is_admin; @Nullable String home_address; @Nullable String phone_number; }A @Dao interface UserDao { @Query("SELECT * FROM user WHERE name LIKE 'JAKE %'") List jakes(); }H

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CREATE TABLE user( id INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT NOT NULL, email TEXT NOT NULL ); SELECT name, email FROM user WHERE name LIKE 'Jake %'

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CREATE TABLE user( id INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT NOT NULL, email TEXT NOT NULL ); SELECT name, email FROM user WHERE name LIKE 'Jake %' data class User( val id: Long, val name: String, val email: String ) data class JakeResult( val name: String, val email: String ) interface UserQueries { fun jakes(): Query }

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Mechanisms of Metaprogramming @JakeWharton