Inline functions in Kotlin

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Jose Flavio Quispe Irrazábal Software Engineer @jflavio11 Inline functions in Kotlin A first approach Android Dev Perú

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In this presentation ● Anonymous classes, functions and lambda expressions. ● Functions in Kotlin. ● Inline functions. ● What is the Java Bytecode? ● Things to keep in mind: return statement. ● Extra

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The beginning

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Anonymous classes, anonymous functions and lambda expressions ● Anonymous classes → create entities from an interface without creating an implementation class. Kotlin Everywhere

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Anonymous classes, anonymous functions and lambda expressions ● Lambdas → reference anonymous functions (or without name). Replace the use of anonymous classes. Kotlin Everywhere

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High Order Functions Functions in Kotlin are first-class: ● They can be passed as parameters ● They can be stored in variables ● They can be returned from another high-order function Kotlin Everywhere

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High Order Functions Kotlin Everywhere But an object is created every time you assigned to a variable or pass it as a parameter to another function

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Simple example Kotlin Everywhere fun myFilter(list: List, funcion: (Double, Double) -> Boolean): List myFilter(teachersList) { ratingYearOne, reatingYearTwo -> (ratingYearOne + reatingYearTwo)/2 >= 7.0 } myFilter(teachersList, new Funcion() { @Override public boolean function(Double ratingYearOne, reatingYearTwo) { return (ratingYearOne + reatingYearTwo)/2 >= 7.0 ; } });

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Inline functions

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Inline functions ● Using inline keyword, we tell the compiler to copy functions and parameters to the call site. ● In normal functions its code is set in memory. Everytime it is tried to be invoked, parameters are added to the memory stack and then it is invoked. Kotlin Everywhere

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Inline functions Kotlin Everywhere

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Decompiled bytecode (without inline)

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Bytecode and JVM Languages?

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JVM Languages ● Every language that runs on the JVM: Scala, Java, Kotlin, Jython, etc. ● Compile to Java Bytecode. Kotlin Everywhere

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Bytecode ● Instruction set of the JVM. ● Then, the JVM is independent of any OS. Kotlin Everywhere

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Bytecode Kotlin Everywhere

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Decompiled bytecode (without inline)

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Inline functions Kotlin Everywhere

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Decompiled bytecode (using inline)

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Inline functions Kotlin Everywhere

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Inline functions ● Using inline keyword, we tell the compiler to copy functions and parameters to the call site. Kotlin Everywhere

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Inline functions To Keep in mind ● Normal “return” statement is not allowed inside a lambda, we must use a label → local return. ● Above behavior, is similar in anonymous functions. Kotlin Everywhere

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Log Found Bart Did we find Bart? End of findStudent

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Inline functions To Keep in mind ● “return” returns the nearest function declaration. ● In lambdas, the enclosing function is where the nearest fun declaration is. Kotlin Everywhere

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Inline functions return statement Kotlin Everywhere

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return statement: decompiled bytecode (without inline) Kotlin Everywhere return ??

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Inline functions Kotlin Everywhere Log Found Bart

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Conclusions

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Inline functions ● Inline functions can reduce memory overhead (and time execution). Kotlin Everywhere ● Increase resulting bytecode. ● We should avoid them in large code logic. ● TODOs (read about) : ○ no inline ○ crossinline ○ refied ● We should keep in mind of return statement.

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Extra

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Kotlin Everywhere Tested in a Macbook Pro early 2015 - i5 - 8GB RAM 1 2 3 4 5 6 7 8 9 10 Average 8432 7354 7840 6846 7633 7139 7113 8085 9147 6873 7646.2 ms Time comparison ● Using inline keyword ● Normal lambda 1 2 3 4 5 6 7 8 9 10 Average 15799 16067 16293 16293 15606 15216 15292 15667 15695 19755 16168.3 ms

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Use of inline functions

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Thank You! Jose Flavio Quispe Irrazábal Software Engineer @jflavio11 Android Dev Perú