is there a `const()`funciton in Kotlin? (or equivalent)

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[Raymond Barlow]

is there a `const()`funciton in Kotlin? (or equivalent)

[benleggiero]

Can you give an example in a language you're more familiar with?

[kevindmoore]

There is the const keyword. What are you trying to achieve?

[Raymond Barlow]

Sure:
Haskell:
const x _ = x

Scala:
const(a: A) = _ => a

[Raymond Barlow]

I can, of course define it myself. Just wondering if it is already defined in the standard libraries.

[Mike]

Some ideas here for an identity function, including { it }. So no built-in identity function, but depending on scenario, some succinct ways to accomplish it.

[Mike]

https://stackoverflow.com/questions/32336436/does-kotlin-have-an-identity-function

[Raymond Barlow]

But what about const?

[Mike]

What am I missing? const looks like it is a function that returns the passed parameter. Identity does the same thing, so aren't they equivalent, just a different name?

[Raymond Barlow]

The difference is that identity() returns what it is given when called. const(a) will always return the value a, no matter what the input.

[Raymond Barlow]

const(5) would be the same as { _ -> 5 }

[Raymond Barlow]

like I said, easy enough to define my own, but it seems like it should be a core function

[Raymond Barlow]

https://www.scala-lang.org/api/current/scala/Function$.html#const%5BT,U%5D(x:T)(y:U):T

[Raymond Barlow]

https://www.scala-lang.org/api/current/scala/Predef$.html#identity%5BA%5D(x:A):A

[Raymond Barlow]

listOf(1,2,3).map(identity()) == listOf(1,2,3)

[Raymond Barlow]

listOf(1,2,3).map(const(5)) == listOf(5,5,5)

[benleggiero]

Aha, I see. I like this idea, and I think that it would have a place in the stdlib. Maybe submit a PR?

[Raymond Barlow]

ok cool 🙂

[Mike]

Thank you for the explanation. The syntax for defining it didn't make it clear the function would always return the same value. So now I understand the difference, but I'm not grasping the use case for it. Time for me to do some research...