Building Robust Software, Episode 2

Presented at https://www.meetkt.org on 21 October 2021

The first episode of this series touched upon leveraging the Kotlin type system, adopting ideas from the functional programming world, leveraging the robustness principle, and failing fast to build robust software.

In this session, we'll focus on the thing that makes software move the word — side-effects. Side-effects are what make tangible changes to the real world with which the software is interacting. These changes could be,

Making network calls
Saving your wishlist on your favorite shopping website
Rendering graphics on the screen so that your favorite video game character can jump over nefarious enemies, collect gold coins, and save the prince or princess from the supervillain.

And naturally, when your program has side-effects that interact with the real world, things can go wrong in so many ways because the world is not a perfect place to live in. What happens when your database is not available, or your disk is full? Your program will throw exceptions because it failed to accomplish the mission you initially set it to.

Exceptions can be painful to deal with. So, we will look into what they are, the implications of using them to decide the control flow of your program, and what patterns you can use to deal with them elegantly.

Finally, we'll finish by looking into how you can design systems and model boundaries between components/classes/functions, therefore, building systems with good testability. This topic will also set the tone for our next session on writing tests!

Transcript

1. Ragunath Jawahar @ragunathjawahar
   https://ragunath.xyz
   Building Robust Software
   Episode 2: Exceptions, side-e
   ff
   ects and boundaries
   

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2. Why?
   • People
   
   • Code
   
   • Process
   
   • Tooling
   

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3. Why?
   • People
   
   • Code
   
   • Process
   
   • Tooling
   

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4. Code
   • Less bureaucracy
   
   • Simple ideas
   
   • Starting point to hone your craft
   

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5. Recap
   • Robustness principle + tweaked version
   
   • Algebraic data types with Kotlin’s sealed classes
   
   • Total & partial functions
   
   • Using types,
   
   • To prevent defensive programming overhead
   
   • To avoid primitive obsession
   

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6. Episode 1
   https://bit.ly/30zwgTy
   

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7. Pendulum swings
   

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8. //
   Primitive obsession
   
   
   val password: String = "super secret stuff!"
   
   
   PasswordValidator.validate(password)
   
   
   //
   Encapsulated type
   
   
   val password: Password = Password("super secret stuff!")
   
   
   password.validate(password)
   

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9. //
   Primitive obsession
   
   
   val password: String = "super secret stuff!"
   
   
   PasswordValidator.validate(password)
   
   
   //
   Encapsulated type
   
   
   val password: Password = Password("super secret stuff!")
   
   
   password.validate(password)
   

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10. //
    Primitive obsession
    
    
    val password: String = "super secret stuff!"
    
    
    PasswordValidator.validate(password)
    
    
    //
    Encapsulated type
    
    
    val password: Password = Password("super secret stuff!")
    
    
    password.validate(password)
    

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11. //
    Primitive obsession
    
    
    val password: String = "super secret stuff!"
    
    
    PasswordValidator.validate(password)
    
    
    //
    Encapsulated type
    
    
    val password: Password = Password("super secret stuff!")
    
    
    password.validate(password)
    

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12. Pendulum swings example
    Primitive obsession
    • Built-in operators (+, -, !,
    & &
    ,
    ||
    , [], etc.,)
    
    • value or inline classes
    
    • ORM and serialisation/deserialisation libraries
    
    • Don’t have enough clarity about the problem domain
    

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13. Exceptions
    

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14. https://docs.oracle.com/javase/tutorial/essential/exceptions/de
    fi
    nition.html
    The term exception is shorthand for the
    phrase “exceptional event.”
    

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15. Treat exceptions as first class citizens.
    

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16. Exceptions
    Anti-patterns
    

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17. try {
    
    
    / /
    make a network call
    
    
    } catch (e: IOException) {
    
    
    / /
    Gulp
    !!
    🥤
    
    
    } catch (e: HttpRetryException) {
    
    
    / /
    Delicious 😋
    
    
    }
    1. Swallowing exceptions
    

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18. try {
    
    
    / /
    make a network call
    
    
    } catch (e: Exception) {
    
    
    showSomethingWentWrong()
    
    
    }
    2. Catch-all
    

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19. private fun isNumber(candidate: String): Boolean {
    
    
    return try {
    
    
    Integer.parseInt(candidate)
    
    
    true
    
    
    } catch (e: NumberFormatException) {
    
    
    false
    
    
    }
    
    
    }
    3. Using exceptions for control flow
    

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20. …
    
    
    Result "xyz.ragunath.benchmark.ReturnValues.returnValueTest":
    
    
    224747599.794 ±(99.9%) 1251327.222 ops/s [Average]
    
    
    (min, avg, max) = (220755995.007, 224747599.794, 227672182.229), stdev = 1670486.041
    
    
    CI (99.9%): [223496272.572, 225998927.016] (assumes normal distribution)
    
    
    …
    
    
    Result "xyz.ragunath.benchmark.StackTraces.stackTraceTest":
    
    
    5830.292 ±(99.9%) 31.441 ops/s [Average]
    
    
    (min, avg, max) = (5676.655, 5830.292, 5889.489), stdev = 41.973
    
    
    CI (99.9%): [5798.851, 5861.733] (assumes normal distribution)
    
    
    …
    

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21. …
    
    
    Result "xyz.ragunath.benchmark.ReturnValues.returnValueTest":
    
    
    224747599.794 ±(99.9%) 1251327.222 ops/s [Average]
    
    
    (min, avg, max) = (220755995.007, 224747599.794, 227672182.229), stdev = 1670486.041
    
    
    CI (99.9%): [223496272.572, 225998927.016] (assumes normal distribution)
    
    
    …
    
    
    Result "xyz.ragunath.benchmark.StackTraces.stackTraceTest":
    
    
    5830.292 ±(99.9%) 31.441 ops/s [Average]
    
    
    (min, avg, max) = (5676.655, 5830.292, 5889.489), stdev = 41.973
    
    
    CI (99.9%): [5798.851, 5861.733] (assumes normal distribution)
    
    
    …
    

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22. …
    
    
    Result "xyz.ragunath.benchmark.ReturnValues.returnValueTest":
    
    
    224747599.794 ±(99.9%) 1251327.222 ops/s [Average]
    
    
    (min, avg, max) = (220755995.007, 224747599.794, 227672182.229), stdev = 1670486.041
    
    
    CI (99.9%): [223496272.572, 225998927.016] (assumes normal distribution)
    
    
    …
    
    
    Result "xyz.ragunath.benchmark.StackTraces.stackTraceTest":
    
    
    5830.292 ±(99.9%) 31.441 ops/s [Average]
    
    
    (min, avg, max) = (5676.655, 5830.292, 5889.489), stdev = 41.973
    
    
    CI (99.9%): [5798.851, 5861.733] (assumes normal distribution)
    
    
    …
    

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23. …
    
    
    Result "xyz.ragunath.benchmark.ReturnValues.returnValueTest":
    
    
    224747599.794 ±(99.9%) 1251327.222 ops/s [Average]
    
    
    (min, avg, max) = (220755995.007, 224747599.794, 227672182.229), stdev = 1670486.041
    
    
    CI (99.9%): [223496272.572, 225998927.016] (assumes normal distribution)
    
    
    …
    
    
    Result "xyz.ragunath.benchmark.StackTraces.stackTraceTest":
    
    
    5830.292 ±(99.9%) 31.441 ops/s [Average]
    
    
    (min, avg, max) = (5676.655, 5830.292, 5889.489), stdev = 41.973
    
    
    CI (99.9%): [5798.851, 5861.733] (assumes normal distribution)
    
    
    …
    

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24. …
    
    
    Result "xyz.ragunath.benchmark.ReturnValues.returnValueTest":
    
    
    224747599.794 ±(99.9%) 1251327.222 ops/s [Average]
    
    
    (min, avg, max) = (220755995.007, 224747599.794, 227672182.229), stdev = 1670486.041
    
    
    CI (99.9%): [223496272.572, 225998927.016] (assumes normal distribution)
    
    
    …
    
    
    Result "xyz.ragunath.benchmark.StackTraces.stackTraceTest":
    
    
    5830.292 ±(99.9%) 31.441 ops/s [Average]
    
    
    (min, avg, max) = (5676.655, 5830.292, 5889.489), stdev = 41.973
    
    
    CI (99.9%): [5798.851, 5861.733] (assumes normal distribution)
    
    
    …
    

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25. …
    
    
    Result "xyz.ragunath.benchmark.ReturnValues.returnValueTest":
    
    
    224747599.794 ±(99.9%) 1251327.222 ops/s [Average]
    
    
    (min, avg, max) = (220755995.007, 224747599.794, 227672182.229), stdev = 1670486.041
    
    
    CI (99.9%): [223496272.572, 225998927.016] (assumes normal distribution)
    
    
    …
    
    
    Result "xyz.ragunath.benchmark.StackTraces.stackTraceTest":
    
    
    5830.292 ±(99.9%) 31.441 ops/s [Average]
    
    
    (min, avg, max) = (5676.655, 5830.292, 5889.489), stdev = 41.973
    
    
    CI (99.9%): [5798.851, 5861.733] (assumes normal distribution)
    
    
    …
    

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26. View Slide

27. for (candidate in potentialNumbers) {
    
    
    if (isNumber(candidate)) {
    
    
    println("It's a number!")
    
    
    } else {
    
    
    println("NaN")
    
    
    }
    
    
    }
    3. Using exceptions for control flow (contd…)
    

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28. Tests
    

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29. assertThat(false).isTrue()
    Tests
    

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30. Exception in thread "main" expected to be true
    
    
    at CanaryTestKt.main(CanaryTest.kt:15)
    
    
    at CanaryTestKt.main(CanaryTest.kt)
    Tests
    

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31. if (balance < requestedAmount) {
    
    
    throw Exception("Meh… 😒")
    
    
    }
    4. Throwing Exception
    

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32. Exception handling in Kotlin
    • No checked exceptions
    
    • try is an expression
    

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33. var guardDogResult: Result
    
    
    try {
    
    
    guardDogResult = getGuardDog()
    
    
    } catch (e: NoGuardDogException) {
    
    
    guardDogResult = Result.failure(e)
    
    
    }
    try expression
    

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34. val guardDogResult: Result = try {
    
    
    getGuardDog()
    
    
    } catch (e: NoGuardDogException) {
    
    
    Result.failure(e)
    
    
    }
    try expression
    

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35. Exception handling patterns
    

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36. 1. Tester-Doer pattern
    • Tester - a member that is used to test a condition
    
    • Doer - a member that performs a potentially throwing operation
    

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37. stack.pop()
    

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38. java.util.EmptyStackException
    
    
    at java.base/java.util.Stack.peek(Stack.java:102)
    
    
    at java.base/java.util.Stack.pop(Stack.java:84)
    
    
    at MainKt.main(Main.kt:8)
    
    
    at MainKt.main(Main.kt)
    

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39. if (stack.isNotEmpty()) {
    
    
    stack.pop()
    
    
    }
    

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40. 2. Try-Parse pattern
    • Unvalidated input data
    
    • tryParse - veri
    fi
    es if the input is valid and can be parsed
    
    • parse - performs the actual parsing
    

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41. if (SerialNumber.tryParse(possiblySerialNumber)) {
    
    
    val serialNumber = SerialNumber.parse(possiblySerialNumber)
    
    
    save(serialNumber)
    
    
    }
    

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42. 3. Converting exceptions to values
    • Non-trivial exceptional conditions
    
    • Exception has domain meaning
    
    • Has to be communicated to the consumer
    
    • Use Kotlin’s sealed classes, data classes and object to provide meaning
    

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43. Registering a new user from a client
    • Successfully creates a user account
    
    • Email already registered
    
    • Validation errors
    
    • Connection errors
    
    • 5xx server errors
    
    • Unknown errors
    

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44. Registering a new user from a client
    • Successfully creates a user account
    
    • Email already registered
    
    • Validation errors
    
    • Connection errors
    
    • 5xx server errors
    
    • Unknown errors
    

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45. SignupResponse.kt
    sealed class SignupResponse {
    
    
    data class AccountCreated(val userId: String) : SignupResponse()
    
    
    data class EmailAlreadyRegistered(val registrationEmail: String) : SignupResponse()
    
    
    data class InputValidationFailed(val errors: List) : SignupResponse()
    
    
    object ConnectionError : SignupResponse()
    
    
    data class ServerError(val statusCode: Int) : SignupResponse()
    
    
    data class UnknownError(val statusCode: Int, val responseBody: String?) : SignupResponse()
    
    
    }
    

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46. Usage
    val response = accountsApi.signup("John Doe", "john@example.org")
    
    
    when (response) {
    
    
    is AccountCreated
    ->
    saveUserId(response.userId)
    
    
    is EmailAlreadyRegistered
    -
    >
    showEmailAlreadyRegistered(response.registrationEmail)
    
    
    is InputValidationFailed
    ->
    showValidationErrors(response.errors)
    
    
    ConnectionError
    ->
    showCheckConnectionMessage()
    
    
    is ServerError, is UnknownError
    ->
    showTryAgainInSometimeMessage()
    
    
    }
    

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47. Exceptions summary
    • Exception handling summary
    
    • Kotlin’s try expression
    
    • Tester-Doer pattern
    
    • Try-Parse pattern
    
    • Converting exceptions to values
    

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48. Boundaries
    

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49. Objective
    • Find attendees that have RSVP’d “Yes” or “Maybe”
    
    • Remind them about an upcoming event
    

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50. class EventManager(
    
    
    private val dao: EventDao,
    
    
    private val mailer: EventMailer
    
    
    ) {
    
    
    fun sendReminder() {
    
    
    val attendees = dao.getAttendees()
    
    
    val potentialAttendees = attendees
    
    
    .filter { it.rsvp
    ==
    Rsvp.YES
    |
    |
    it.rsvp
    ==
    Rsvp.MAYBE }
    
    
    potentialAttendees
    
    
    .onEach { mailer.mail(it) }
    
    
    }
    
    
    }
    

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51. class EventManager(
    
    
    private val dao: EventDao,
    
    
    private val mailer: EventMailer
    
    
    ) {
    
    
    fun sendReminder() {
    
    
    val attendees = dao.getAttendees()
    
    
    val potentialAttendees = attendees
    
    
    .filter { it.rsvp
    ==
    Rsvp.YES
    |
    |
    it.rsvp
    ==
    Rsvp.MAYBE }
    
    
    potentialAttendees
    
    
    .onEach { mailer.mail(it) }
    
    
    }
    
    
    }
    

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52. class EventManager(
    
    
    private val dao: EventDao,
    
    
    private val mailer: EventMailer
    
    
    ) {
    
    
    fun sendReminder() {
    
    
    val attendees = dao.getAttendees()
    
    
    val potentialAttendees = attendees
    
    
    .filter { it.rsvp
    ==
    Rsvp.YES
    |
    |
    it.rsvp
    ==
    Rsvp.MAYBE }
    
    
    potentialAttendees
    
    
    .onEach { mailer.mail(it) }
    
    
    }
    
    
    }
    

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53. class EventManager(
    
    
    private val dao: EventDao,
    
    
    private val mailer: EventMailer
    
    
    ) {
    
    
    fun sendReminder() {
    
    
    val attendees = dao.getAttendees()
    
    
    val potentialAttendees = attendees
    
    
    .filter { it.rsvp
    ==
    Rsvp.YES
    |
    |
    it.rsvp
    ==
    Rsvp.MAYBE }
    
    
    potentialAttendees
    
    
    .onEach { mailer.mail(it) }
    
    
    }
    
    
    }
    

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54. class EventManager(
    
    
    private val dao: EventDao,
    
    
    private val mailer: EventMailer
    
    
    ) {
    
    
    fun sendReminder() {
    
    
    val attendees = dao.getAttendees()
    
    
    val potentialAttendees = attendees
    
    
    .filter { it.rsvp
    ==
    Rsvp.YES
    |
    |
    it.rsvp
    ==
    Rsvp.MAYBE }
    
    
    potentialAttendees
    
    
    .onEach { mailer.mail(it) }
    
    
    }
    
    
    }
    

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55. class EventManager(
    
    
    private val dao: EventDao,
    
    
    private val mailer: EventMailer
    
    
    ) {
    
    
    fun sendReminder() {
    
    
    val attendees = dao.getAttendees()
    
    
    val potentialAttendees = attendees
    
    
    .filter { it.rsvp
    ==
    Rsvp.YES
    |
    |
    it.rsvp
    ==
    Rsvp.MAYBE }
    
    
    potentialAttendees
    
    
    .onEach { mailer.mail(it) }
    
    
    }
    
    
    }
    

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56. class EventManager(
    
    
    private val dao: EventDao,
    
    
    private val mailer: EventMailer
    
    
    ) {
    
    
    fun sendReminder() {
    
    
    val attendees = dao.getAttendees()
    
    
    val potentialAttendees = attendees
    
    
    .filter { it.rsvp
    ==
    Rsvp.YES
    |
    |
    it.rsvp
    ==
    Rsvp.MAYBE }
    
    
    potentialAttendees
    
    
    .onEach { mailer.mail(it) }
    
    
    }
    
    
    }
    

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57. class EventManager(
    
    
    private val dao: EventDao,
    
    
    private val mailer: EventMailer
    
    
    ) {
    
    
    fun sendReminder() {
    
    
    val attendees = dao.getAttendees()
    
    
    val potentialAttendees = attendees
    
    
    .filter { it.rsvp
    ==
    Rsvp.YES
    |
    |
    it.rsvp
    ==
    Rsvp.MAYBE }
    
    
    potentialAttendees
    
    
    .onEach { mailer.mail(it) }
    
    
    }
    
    
    }
    

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58. class EventManager(
    
    
    private val dao: EventDao,
    
    
    private val mailer: EventMailer
    
    
    ) {
    
    
    fun sendReminder() {
    
    
    val attendees = dao.getAttendees()
    
    
    val potentialAttendees = attendees
    
    
    .filter { it.rsvp
    ==
    Rsvp.YES
    |
    |
    it.rsvp
    ==
    Rsvp.MAYBE }
    
    
    potentialAttendees
    
    
    .onEach { mailer.mail(it) }
    
    
    }
    
    
    }
    

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59. class EventManager(
    
    
    private val dao: EventDao,
    
    
    private val mailer: EventMailer
    
    
    ) {
    
    
    fun sendReminder() {
    
    
    val attendees = dao.getAttendees()
    
    
    val potentialAttendees = attendees
    
    
    .filter { it.rsvp
    ==
    Rsvp.YES
    |
    |
    it.rsvp
    ==
    Rsvp.MAYBE }
    
    
    potentialAttendees
    
    
    .onEach { mailer.mail(it) }
    
    
    }
    
    
    }
    

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60. class EventManager(
    
    
    private val dao: EventDao,
    
    
    private val mailer: EventMailer
    
    
    ) {
    
    
    fun sendReminder() {
    
    
    val attendees = dao.getAttendees()
    
    
    val potentialAttendees = attendees
    
    
    .filter { it.rsvp
    ==
    Rsvp.YES
    |
    |
    it.rsvp
    ==
    Rsvp.MAYBE }
    
    
    potentialAttendees
    
    
    .onEach { mailer.mail(it) }
    
    
    }
    
    
    }
    

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61. Values as boundaries
    

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62. fun List.attending(): List {
    
    
    return filter { it.rsvp
    ==
    Rsvp.YES
    |
    |
    it.rsvp
    ==
    Rsvp.MAYBE }
    
    
    }
    

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63. fun List.attending(): List {
    
    
    return filter { it.rsvp
    ==
    Rsvp.YES
    |
    |
    it.rsvp
    ==
    Rsvp.MAYBE }
    
    
    }
    

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64. fun List.attending(): List {
    
    
    return filter { it.rsvp
    ==
    Rsvp.YES
    |
    |
    it.rsvp
    ==
    Rsvp.MAYBE }
    
    
    }
    

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65. class EventManager(
    
    
    private val dao: EventDao,
    
    
    private val mailer: EventMailer
    
    
    ) {
    
    
    fun sendReminder() {
    
    
    dao.getAttendees()
    
    
    .attending()
    
    
    .onEach { mailer.mail(it) }
    
    
    }
    
    
    }
    

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66. class EventManager(
    
    
    private val dao: EventDao,
    
    
    private val mailer: EventMailer
    
    
    ) {
    
    
    fun sendReminder() {
    
    
    dao.getAttendees()
    
    
    .attending()
    
    
    .onEach { mailer.mail(it) }
    
    
    }
    
    
    }
    

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67. class EventManager(
    
    
    private val dao: EventDao,
    
    
    private val mailer: EventMailer
    
    
    ) {
    
    
    fun sendReminder() {
    
    
    dao.getAttendees()
    
    
    .attending()
    
    
    .onEach { mailer.mail(it) }
    
    
    }
    
    
    }
    

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68. class EventManager(
    
    
    private val dao: EventDao,
    
    
    private val mailer: EventMailer
    
    
    ) {
    
    
    fun sendReminder() {
    
    
    dao.getAttendees()
    
    
    .attending()
    
    
    .onEach { mailer.mail(it) }
    
    
    }
    
    
    }
    

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69. class EventManager(
    
    
    private val dao: EventDao,
    
    
    private val mailer: EventMailer
    
    
    ) {
    
    
    fun sendReminder() {
    
    
    dao.getAttendees()
    
    
    .attending()
    
    
    .onEach { mailer.mail(it) }
    
    
    }
    
    
    }
    

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70. class EventManager(
    
    
    private val dao: EventDao,
    
    
    private val mailer: EventMailer
    
    
    ) {
    
    
    fun sendReminder() {
    
    
    dao.getAttendees()
    
    
    .attending()
    
    
    .onEach { mailer.mail(it) }
    
    
    }
    
    
    }
    

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71. class EventManager(
    
    
    private val dao: EventDao,
    
    
    private val mailer: EventMailer
    
    
    ) {
    
    
    fun sendReminder() {
    
    
    dao.getAttendees()
    
    
    .attending()
    
    
    .onEach { mailer.mail(it) }
    
    
    }
    
    
    }
    

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72. class EventManager(
    
    
    private val dao: EventDao,
    
    
    private val mailer: EventMailer
    
    
    ) {
    
    
    fun sendReminder() {
    
    
    dao.getAttendees()
    
    
    .attending()
    
    
    .onEach { mailer.mail(it) }
    
    
    }
    
    
    }
    

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73. class EventManager(
    
    
    private val dao: EventDao,
    
    
    private val mailer: EventMailer
    
    
    ) {
    
    
    fun sendReminder() {
    
    
    dao.getAttendees()
    
    
    .attending()
    
    
    .onEach { mailer.mail(it) }
    
    
    }
    
    
    }
    

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74. class EventManager(
    
    
    private val dao: EventDao,
    
    
    private val mailer: EventMailer
    
    
    ) {
    
    
    fun sendReminder() {
    
    
    dao.getAttendees()
    
    
    .attending()
    
    
    .onEach { mailer.mail(it) }
    
    
    }
    
    
    }
    

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75. class EventManager(
    
    
    private val dao: EventDao,
    
    
    private val mailer: EventMailer
    
    
    ) {
    
    
    fun sendReminder() {
    
    
    dao.getAttendees()
    
    
    .attending()
    
    
    .onEach { mailer.mail(it) }
    
    
    }
    
    
    }
    

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76. class EventManager(
    
    
    private val dao: EventDao,
    
    
    private val mailer: EventMailer
    
    
    ) {
    
    
    fun sendReminder() {
    
    
    dao.getAttendees()
    
    
    .attending()
    
    
    .onEach { mailer.mail(it) }
    
    
    }
    
    
    }
    

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77. Testing (Isolated for logic & Integrated for effects)
    • No attendees
    
    • All RSVP’d “Yes”
    
    • All RSVP’d “No”
    
    • All RSVP’d “Maybe”
    
    • Mix of “Yes”, “No”, “Maybe”
    • Query database, Send email
    

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78. class EventManager(
    
    
    private val dao: EventDao,
    
    
    private val mailer: EventMailer
    
    
    ) {
    
    
    fun sendReminder() {
    
    
    val attendees = dao.getAttendees()
    
    
    val potentialAttendees = attendees
    
    
    .filter { it.rsvp
    ==
    Rsvp.YES
    |
    |
    it.rsvp
    ==
    Rsvp.MAYBE }
    
    
    potentialAttendees
    
    
    .onEach { mailer.mail(it) }
    
    
    }
    
    
    }
    Testing 😱
    

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79. Testing (Isolated for logic & Integrated for effects)
    • No attendees
    
    • All RSVP’d “Yes”
    
    • All RSVP’d “No”
    
    • All RSVP’d “Maybe”
    
    • Mix of “Yes”, “No”, “Maybe”
    • Query database, Send email
    

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80. class EventManager(
    
    
    private val dao: EventDao,
    
    
    private val mailer: EventMailer
    
    
    ) {
    
    
    fun sendReminder() {
    
    
    dao.getAttendees()
    
    
    .attending()
    
    
    .onEach { mailer.mail(it) }
    
    
    }
    
    
    }
    Testing 🥳
    

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81. Core
    • Path +
    
    • Dependencies -
    
    • Isolated tests
    Shell
    • Path -
    
    • Dependencies +
    
    • Integrated tests
    

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82. https://github.com/redgreenio/
    fl
    uid
    

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83. Value as boundaries in the wild
    • HTTP
    
    • IPC
    
    • RPC
    
    • Actor-based systems
    
    • Event-driven systems
    
    • Message queues
    
    • Event streams
    

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84. Architectures
    • Functional core & imperative shell
    
    • Hexagonal architecture
    
    • Ports & adapters
    
    • Redux
    

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85. References
    • https://docs.oracle.com/javase/tutorial/essential/exceptions/index.html
    
    • https://kotlinlang.org/docs/exceptions.html
    
    • https://radio-weblogs.com/0122027/stories/2003/04/01/JavasCheckedExceptionsWereAMistake.html
    
    • https://www.artima.com/articles/the-trouble-with-checked-exceptions
    
    • https://www.destroyallsoftware.com/talks/boundaries
    
    • https://github.com/spotify/mobius
    
    • https://github.com/redgreenio/fluid
    

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86. Questions?
    
    
    @ragunathjawahar • https:
    /
    /
    ragunath.xyz
    

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