Would love to see a .when extension added to the language

Language Design
1

I have mentioned this before but it would be nice to have .when expression in the language as in

someResult.when {
    success -> a()
    someCondition() -> b()
    else -> c()
}

This is just syntactic sugar for this, but I think it is clearer:

someResult.run {
    when {
        success -> a()
        someCondition() -> b()
        else -> c()
    }
}

Unlike many other features thus is not something you can create in an extension without language changes

1 Like
2

Just thinking out loud:

A great extension of this function would be to add the function-type as a special type of function (like infix) as well.
Ofcourse, when itself like proposed will only work as described above, because when is a reserved keyword.

Then you can:

  • control the variable you are matching on
  • add a custom scope in which you can provide variables to match against
  • control its return type inside the lambda, such that you can control the entire lambda.
  • return another type from the function itself, probably a builder of some kind.
  • give it different names, which match the DSL better.

I don’t know if my extension is worth all the trouble of adding it, but it’s just a fun idea this reminded me of…

3

Do you mean something like this? I have never seen the second version, not sure it even compiles.

someResult.run {
    when(this) {
        success -> a()
        someCondition() -> b()
        else -> c()
    }
}
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4

This is as concise as your proposal:

when(someResult) {
    success -> a()
    someCondition() -> b()
    else -> c()
}

The problem arises only when we want to chain it in functional expressions. I would prepare a better example to make this clear.

5

I didn’t make it clear in my case but the idea is that success, someCondition, a, b, and c could be properties/functions/extensions on someResult so this is not equivalent at all. It would require putting someResult into a variable (I was not assuming that someResult was a variable and could be a complex expression) and then prefixing all those things with that variable name.

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