Add matchers for Result

[sksamuel]

Jetbrains added the Result type, a bit like the Try type from arrow.
We should add matchers for this.

[faogustavo]

I was trying to do this, but, unfortunately, I started to face some kotlin issues (I guess).
For some unknowing reason, the generic types influence on the Result class.
Here is the snippet that I made to test this.

/**
 * You can edit, run, and share this code. 
 * play.kotlinlang.org 
 */

fun main() {
    val result = Result.runCatching { "Test 01" }
    val errorResult = Result.runCatching { throw java.io.IOException("Some error happened") }
    
    println("Test")
    println(test("Test 01", result))
    println(test("Some error happened", errorResult))
    
    println()
    println("With generics")
    println(match("Test 01", "Some error happened").test(result))
    println(match("Test 01", "Some error happened").test(errorResult))
    
    println()
    println("With kotlintest dsl-like")
    println(result should match("Test 01", "Some error happened"))
    println(errorResult should match("Test 01", "Some error happened"))
}

infix fun <T> T.should(matcher: Matcher<T>) = matcher.test(this)

fun test(expectedValue: String, result: Result<String>) = if (result.isSuccess) {
    expectedValue == result.getOrNull()
} else {
    expectedValue == result.exceptionOrNull()?.message
}

fun <T> match(expectedValue: T, errorMessage: String) = object: Matcher<Result<T>> {
    override fun test(value: Result<T>) = if (value.isSuccess) {
        print("I'm a success")
        Pair(
            value.getOrNull() == expectedValue,
            Pair(value.getOrNull(), expectedValue)
        )
    } else {
        print("I'm an error")
        Pair(
            value.exceptionOrNull()?.message == errorMessage,
            Pair(value.exceptionOrNull()?.message, errorMessage)
        )
    }
}

interface Matcher<T> {
    fun test(value: T): Pair<Boolean, Pair<Any?, Any?>>
}

The result is this 👇

Test
true
true

With generics
I'm a success - (false, (Success(Test 01), Test 01))
I'm a success - (false, (Failure(java.io.IOException: Some error happened), Test 01))

With kotlintest dsl-like
I'm a success - (false, (Success(Test 01), Test 01))
I'm a success - (false, (Failure(java.io.IOException: Some error happened), Test 01))

For some reason, when I pass the result to a generic, it creates a new "Success Result" and instead of getting "Test 01" from the .getOrNull(), its returning Success(Test 01).
The same is reproducible with the exceptions. When I send a failure, it becomes a Success(Failure(TesteException)).
I'll see if I can find some related bug on kotlin reporitory, but I think this issue will be blocked until we understand what is going on.

[faogustavo]

@sksamuel @Kerooker ☝️

---

I also create an issue on kotlin issue tracker. Didn't find any similar bug.

[LeoColman]

I see.

I'll comment about this in KotlinLang's Slack, let's see if it's indeed a bug.

We can keep this on-hold for a bit :/

[Dico200]

The type T is a Result itself. So your value in your test override is a Result<Result<*>>

[Dico200]

Please swap the generics for concrete types and see if you can find the problem, this code is very unreadable here like this

[faogustavo]

Please swap the generics for concrete types and see if you can find the problem, this code is very unreadable here like this

As I showed on the code that I posted before, I already tried without generic and it works. Unfortunately, the entire library is built upon those generics and doesn't make any sense to change that. Or even create a lot of repetition just for that.

They commented on the issue on kotlin issue tracker that it's a bug on kotlin/jvm about boxing/unboxing. They already added the task as a subtask from another group and maybe will have a solution after some time.

[sksamuel]

What's wrong with something like this: https://pl.kotl.in/zpkSnkEeD
That works, and you can add in the shouldBeFailure complement.

[faogustavo]

What's wrong with something like this: https://pl.kotl.in/zpkSnkEeD
That works, and you can add in the shouldBeFailure complement.

The problem is when you add one more level of complexity like this.
There is an issue that makes our syntax buggy.
If you look carefully, you will see that in the message, instead of getting Expecting Success(Test 01) to be Wibble, we go Expecting Success(Success(Test 01)) to be Wibble. There is an "extra" Success being "added" when the value is passed as a parameter with all those levels using generics.

[sksamuel]

We could do it without the infix version for now: https://pl.kotl.in/5RZM9cKCT
And then add the infix version once they fix the bug ?