Droidcon Berlin: 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?

Just because we might not be exposing a module as a public or open-sourced library, doesn't mean we can't benefit from making good decisions towards an effective and sensible API. By taking the stance that every piece of code we write is an API we can build more versatile and scalable applications.

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
   Android & Kotlin GDE Berlin
   @askashdavies
   Everything is an API
   OMG IRL INORITE?!
   Droidcon Berlin - Oct 21’ 󰎲
   

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2. 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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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.
   

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4. Communication
   
   
   
   

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

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6. 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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7. 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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8. 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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9. ● SOAP (XML)
   ● RESTful (JSON)
   ● GraphQL
   ● gRPC (Proto)
   APIs Protocols
   Just a small slice...
   

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10. Hierarchy
    APIs
    

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11. 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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12. 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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14. ¯\_(ツ)_/¯
    

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

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

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19. Good Code? 🏆
    

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

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

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

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

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27. Meaningful Names
    Naming is hard.
    

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

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

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

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31. 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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32. 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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33. 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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34. 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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35. Meaningful Naming
    internal suspend infix fun String.contains(value: String): Boolean
    Signatures
    

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36. 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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37. 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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38. 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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39. Meaningful Naming
    public interface ViewStateFactory { /* ... */ }
    internal class ViewStateFactoryImpl { /* ... */ }
    Interfaces
    

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40. 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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41. 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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42. 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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43. ● 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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44. The elephant in the room...
    

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45. Modularisation
    “Modularise all the things!”
    

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46. Modularisation
    Concurrency
    

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47. Modularisation
    Build Cache / Scan
    gradle.com
    

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

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49. ● 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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50. @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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51. 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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52. ● 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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53. ● 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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54. “Every line of code is written without
    reason, maintained out of weakness, and
    deleted by chance”
    - Jean-Paul Sartre
    

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55. ● 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
    

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56. ● Monkey User (monkeyuser.com)
    ● Untitled Goose Game (goose.game)
    Everything is an API
    Easter Eggs
    

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57. Ash Davies
    Android & Kotlin GDE Berlin
    @askashdavies
    Thanks!
    

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