Android Makers Paris: Everything is an API

When creating a new app module, or modularising an existing one, it becomes easy to forget who might be consuming it. It becomes easy to forget that every decision you make will affect how it is used, or in the worst case, abused. We're told that code should document itself, but how do these design decisions reflect in the understanding of intended use?

In this talk, I'll discuss how you can apply best practices from the open-source world to your project, to guard implementations, provide concise and specific contracts, practical documentation mechanisms, and how doing so can aid (or harm) your build time.

Transcript

1. Ash Davies GDE Berlin @askashdavies Everything is an API Android Makers Paris - Avril
2. What defines an API?
3. Application Programming Interface noun A set of functions and procedures allowing the creation of applications that access the features or data of an operating system, application, or other service.
5. /** * An utility class that provides {@code ViewModels} for a scope. * <p> * Default {@code ViewModelProvider} for an {@code Activity} or a {@code Fragment} can be obtained * by passing it to {@link ViewModelProvider#ViewModelProvider(ViewModelStoreOwner)}. */ @SuppressWarnings("WeakerAccess") public class ViewModelProvider { private static final String DEFAULT_KEY = "androidx.lifecycle.ViewModelProvider.DefaultKey"; /** * Implementations of {@code Factory} interface are responsible to instantiate ViewModels. */ public interface Factory { /** * Creates a new instance of the given {@code Class}. * <p> * * @param modelClass a {@code Class} whose instance is requested * @param <T> The type parameter for the ViewModel. * @return a newly created ViewModel */ @NonNull <T extends ViewModel> T create(@NonNull Class<T> modelClass); } }
6. class ItemStateRepository internal constructor(/* ... */) { fun addToFavouritesAndMarkAsRead(itemId: String): Single<Boolean> = /* ... */ fun markItemAsRead(itemId: String): Completable = /* ... */ fun observable(): Observable<ItemStateChange> = /* ... */ fun observableFavouriteChange(): Observable<IsFavourite> = /* ... */ fun observableHiddenChange(): Observable<IsHidden> = /* ... */ fun observableMarkAsReadChange(): Observable<MarkedAsRead> = /* ... */ fun setItemState(itemId: String, isFavourite: Boolean): Completable = /* ... */ fun setHiddenState(itemId: String, isHidden: Boolean): Completable = /* ... */ fun stateFor(itemId: String): Observable<ItemState> = /* ... */ fun states(): Observable<ItemStates> = /* ... */ fun readStateFor(itemId: String): Observable<Boolean> = /* ... */ }
7. ¯\_(ツ)_/¯
8. • Increased learning curve • Longer to peer review • Unpleasant to resolve • Increased risk of bugs • Slowed feature delivery API Decisions Cost of Technical Debt
9. “Debugging is like being the detective in a crime movie where you are also the murderer” - Filipe Fortes
10. • Your code will always be consumed by other people • Technical debt is not often resolved or paid back • Have respect for your colleagues, make their lives easier • Test code should also be considered production ready API Decisions Double standards
11. “Always code as if the guy who ends up maintaining your code will be a violent psychopath who knows where you live” - John Woods
12. Good Code?
13. • No such thing as perfect code • Perfect is the enemy of good • Perfect solution fallacy (Nirvana fallacy) • Problem for API maintainers • Done is ok, work on making it better Good Code?! Not so easy...
14. “Dans ses écrits, un sage Italien, dit que le mieux est l'ennemi du bien” - Voltaire (François-Marie Arouet)
15. • Keep your API surface as small as possible • Allow yourself room for change • Try not to expose behaviour Code Progressively Through abstraction...
16. • Prefer interface contracts • Composition over inheritance • Interface segregation principle • Single responsibility principle Hiding Implementations... Through abstraction...
17. • Javadoc can sometimes be useful if maintained • Code should always be self-documenting • Name considerably and with purpose • Consider sources of code smell Usefulness of Documentation “What’s a Javadoc?!”
18. • Conditional statements • Iteration or recursion • Significant indentation • Polymorphism • Mutability Code Smell “My God! What is that smell?” - Veronica Corningstone
19. “There are only two hard things in Computer Science: cache invalidation and naming things” - Phil Karlton
20. Meaningful Names Naming is hard.
21. Meaningful Naming for (i: Int in kS) { try { c.connect(i) } catch(e: Throwable) { // Meh ‍♂ } } Unclear purpose or intention
22. Meaningful Naming for (index: Int in keySet) { try { client.connect(index) } catch(ignored: Throwable) { } } Unclear purpose or intention
23. Meaningful Naming internal suspend infix fun String.contains(value: String): Boolean Signatures
24. Meaningful Naming internal suspend infix fun String.contains(value: String): Boolean Signatures Method is visible only to members in the same package (probably inaccessible)
25. Meaningful Naming internal suspend infix fun String.contains(value: String): Boolean Signatures Method will return a result asynchronously, can only be accessed by coroutine or by another suspended method
26. Meaningful Naming internal suspend infix fun String.contains(value: String): Boolean Signatures Method can be used with the Kotlin infix notation Eg. val result: Boolean = “12345” contains “234”
27. Meaningful Naming internal suspend infix fun String.contains(value: String): Boolean Signatures Receiver indicates the scope of the function, must be called as an extension on this type
28. Meaningful Naming internal suspend infix fun String.contains(value: String): Boolean Signatures
29. Meaningful Naming internal suspend infix fun String.contains(value: String): Boolean Signatures Named parameters with type give us information about how to call the method
30. Meaningful Naming internal suspend infix fun String.contains(value: String): Boolean Signatures Method return type tells us how to use the result
31. Meaningful Naming fun updateClaimWithPolicyDetails(c: Claim, pc: PolicyCriteria, identifier: String) fun getIfNotSetWithDefault(value: Any): String fun compareAndSet(value: Any): Boolean fun isNullOrEmpty(value: String): Boolean Signatures
32. Meaningful Naming public interface ViewStateFactory { /* ... */ } internal class ViewStateFactoryImpl { /* ... */ } Interfaces
33. Impure Functions var values: MutableMap<Char, Int> = mutableMapOf('a' to 1) fun modify(items: MutableMap<Char, Int>): Int { val b: Int = 1; items['a'] = items['a'] * b + 2; return items['a']; } val c = modify(values);
34. Interface Composition Prefer interface composition over inheritance • Inheritance forces the consumer to use a base class • Limitations on extending abstract classes • Potentially exposes protected behaviour • Prohibits Kotlin interface delegation
35. Interface Abstraction public interface CoroutineScope { public val coroutineContext: CoroutineContext } internal class ContextScope(context: CoroutineContext) : CoroutineScope { override val coroutineContext: CoroutineContext = context } public fun CoroutineScope(context: CoroutineContext): CoroutineScope { return ContextScope(if (context[Job] != null) context else context + Job()) } Obfuscate behaviour through interface abstraction
36. • Impact analysis, risk containment • Peer review scrutiny • Mob programming • Android API council • Guild meetings Democratise your API Decisions But not too much!
37. The elephant in the room...
38. Modularisation “Modularise all the things!”
39. Modularisation Parallelisation
40. Modularisation Build Cache / Scan gradle.com
41. Modularisation Pitfalls • Misaligned product flavours • Misbehaving dependencies • Incorrect configurations
43. • Always a potential for risk • Make use of annotations! ◦ @Deprecated(message: String, replaceWith: ReplaceWith, level: DeprecationLevel) ◦ @RequiresOptIn(message: String, level: Level) ◦ @TechnicalDebt(issue: String, message: String) ◦ @VisibleForModularisation(otherwise: ProductionVisibility) But, we’re all human… ‍♂
44. @Deprecated( message = "CoroutineScope.rxCompletable is deprecated in favour of top-level rxCompletable", level = DeprecationLevel.ERROR, replaceWith = ReplaceWith("rxCompletable(context, block)") ) public fun CoroutineScope.rxCompletable( context: CoroutineContext = EmptyCoroutineContext, block: suspend CoroutineScope.() -> Unit ): Completable = rxCompletableInternal(this, context, block) We’re all Human ‍♂ Migration Tools
45. Half screen photo slide if text is necessary We’re all Human ‍♂ Decision Paralysis The worst decision is a decision not made in time.
46. • code that documents itself? • code that can be changed easily? • easily and readily maintainable? • follows all the design principles? Conclusion Good code is...
47. • code that documents itself? • code that can be changed easily? • easily and readily maintainable? • follows all the design principles? • code that can be easily deleted. Conclusion Good code is...
48. “Every line of code is written without reason, maintained out of weakness, and deleted by chance” - Jean-Paul Sartre
49. • Explicit mode for library authoring · Issue #45 · Kotlin/KEEP • TwoHardThings • The Annotated Programmer - Pointer IO • Developers: Your Poorly Named Variables Are Hurting Your Team • How modularization can speed up your Android app's built time • Stefan Tilkov on Twitter: "Many enterprise IT departments have become big fans of an “API-first“ strategy" • The Human Cost of Tech Debt • Unreachable State Everything is an API Further Reading
50. Ash Davies GDE Berlin @askashdavies Merci!