Kotlin User Group Berlin: Everything is an API

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Everything is an API Kotlin User Group Berlin - Mai 23’ 󰎲 Ash Davies Android / Kotlin GDE - Berlin [email protected]

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What is an API? Article Periodocal Incollection…? Accountable Property Inventory...? Acquisition Program Integration…? Academic Performance Index…? Asset Priority Index....? Annual Parasite Incidence…?

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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.

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Communication

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Language 🗣 󰎼 ¿Qué tal? 󰧻 Helô 󰏃 Salut! 󰑒 Pryvit 󰏅 Hello! 󰏢 Ciao 󰎩 Nǐ hǎo 󰎲 Hallo 󰐨 Oi 󰎺 Ahlan 󰏮Anyoung 󰐴 Hej 󰏏 Yassou 󰑍 Selam

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Application Programming Interface Representational State Transfer Simple Object Access Protocol Remote Procedure Call Transactional Agreement Protocol Atomic Resource Translation Application Programming Interface

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APIs curl \ -H "Accept: application/vnd.github.v3+json" \ https://api.github.com/repos/octocat/hello-world/actions/artifacts What does an API look like?

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APIs { "total_count": 2, "artifacts": [ { "id": 11, "node_id": "MDg6QXJ0aWZhY3QxMQ==", "name": "Rails", "size_in_bytes": 556, "url": "https://api.github.com/repos/octo-org/octo-docs/actions/artifacts/11", "archive_download_url": "https://api.github.com/repos/octo-org/octo-docs/actions/artifacts/11/zip", "updated_at": "2020-02-21T14:59:22Z" } ] What does an API look like?

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● SOAP (XML) ● RESTful (JSON) ● GraphQL ● gRPC (Proto) APIs Protocols Just a small slice... monkeyuser.com

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Hierarchy APIs

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Android API Council android.googlesource.com /platform/developers/docs /+/refs/heads/master /api-guidelines/index.md QR Codes? In 2021? Srsly?

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Software Development Kit noun A set of tools for third-party developers to use in producing applications using a particular framework or platform. "the documentation and SDKs have already been updated to reflect the new capabilities"

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¯\_(ツ)_/¯

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● Increased learning curve ● Longer to peer review ● Unpleasant to resolve ● Increased risk of bugs ● Slowed feature delivery API Decisions Cost of Technical Debt

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“Debugging is like being the detective in a crime movie where you are also the murderer” - Filipe Fortes

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● 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

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“Always code as if the guy [sic] who ends up maintaining your code will be a violent psychopath who knows where you live” - John Woods

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Good Code? 🏆

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● 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...

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“Dans ses écrits, un sage Italien, dit que le mieux est l'ennemi du bien” - Voltaire (François-Marie Arouet)

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● Keep your API surface as small as possible ● Allow yourself room for change ● Try not to expose behaviour Code Progressively Through abstraction...

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● Prefer interface contracts ● Composition over inheritance ● Interface segregation principle ● Single responsibility principle Hiding Implementations... Through abstraction...

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● 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?!”

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● Conditional statements ● Iteration or recursion ● Polymorphism ● Mutability ● Significant indentation Code Smell 👃 “My God! What is that smell?” - Veronica Corningstone

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“There are only two hard things in Computer Science: cache invalidation and naming things” - Phil Karlton

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Meaningful Names Naming is hard.

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Meaningful Naming for (i: Int in kS) { try { c.connect(i) } catch (e: Throwable) { // Meh 󰤇 } } Unclear purpose or intention

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Meaningful Naming for (index: Int in keySet) { try { client.connect(index) } catch (ignored: Throwable) { } } Unclear purpose or intention

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Meaningful Naming for (index: Int in keySet) { try { client.connect(index) } catch (ignored: IndexOutOfBoundsException) { } } Unclear purpose or intention

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Meaningful Naming internal suspend infix fun String.contains(value: String): Boolean Signatures

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Meaningful Naming internal suspend infix fun String.contains(value: String): Boolean Signatures Method is visible only to members in the same package

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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

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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”

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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

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Meaningful Naming internal suspend infix fun String.contains(value: String): Boolean Signatures

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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

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Meaningful Naming internal suspend infix fun String.contains(value: String): Boolean Signatures Method return type tells us how to use the result

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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

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Meaningful Naming public interface ViewStateFactory { /* ... */ } internal class ViewStateFactoryImpl { /* ... */ } Interfaces

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Impure Functions var values: MutableMap = mutableMapOf('a' to 1) fun modify(items: MutableMap): Int { val b: Int = 1; items['a'] = items['a'] * b + 2; return items['a']; } val c = modify(values);

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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

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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

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Impact analysis, risk containment Peer review scrutiny Mob programming Android API council Guild meetings Democratise your API Decisions But not too much!

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The elephant in the room...

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Modularisation “Modularise all the things!”

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Modularisation Concurrency

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Modularisation Build Cache / Scan gradle.com

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Modularisation Pitfalls ● Misaligned product flavours ● Misbehaving dependencies ● Incorrect configurations

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● 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… 󰤇

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@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

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Decision-Making Hype Driven Development [email protected]

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Half screen photo slide if text is necessary We’re all Human 󰤇 Decision Paralysis The worst decision is a decision not made in time.

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● Code that documents itself? ● Code that can be changed easily? ● Easily and readily maintainable? ● Follows all the design principles? Conclusion Good code is...

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● 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...

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“Every existing thing is born without reason, prolongs itself out of weakness and dies by chance.” - Jean-Paul Sartre

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“Every line of code is written without reason, maintained out of weakness, and deleted by chance” - Jean-Paul Sartre

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Explicit mode for library authors (Kotlin) TwoHardThing (Martin Fowler) The Annotated Programmer (Chet Haase) Developers: Your Poorly Named Variables Are Hurting Your Team (Bennett Garner) How modularization can speed up your Android app's built tim (Nikita Kozlov) Stefan Tilkov on Twitter: "Many enterprise IT departments have become big fans of an “API-first“ strategy" The Human Cost of Tech Deb (Erik Dietrich) Everything is an API Further Reading

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Thanks! Ash Davies - Cat Person Android / Kotlin GDE - Berlin [email protected]