I m dealing with function overloading when the parameters are lambdas and stumbled upon the following case ```fun foo block String String gt Unit fun foo block gt Unit fun main foo it String gt calls foo block String String gt Unit foo ERROR how to call foo block gt Unit ``` Basically is there a way to specify in the second case that I want to call `foo block gt Unit ` When I specified the type of the lambda argument it seemed that the compiler was able to figure it out however `it Unit` doesn t work for the second case

Apparently this is part of <https kotlinlang org docs reference grammar html|the official grammar> gt lambdaLiteral used by <https kotlinlang org docs reference grammar html annotatedLambda|annotatedLambda> <https kotlinlang org docs reference grammar html functionLiteral|functionLiteral> gt <https kotlinlang org docs reference grammar html statements|statements> gt | <https kotlinlang org docs reference grammar html lambdaParameters|lambdaParameters> gt <https kotlinlang org docs reference grammar html statements|statements> gt that question mark means 0 or 1 of the item and lambdaParameters defines the whole list of parameters and so according to the grammar you can have no parameters but still use the ` gt ` before your statements So I guess it is documented and expected behaviour it s just that no one actually mentions it anywhere outside of the grammar

I m dealing with function overloading when the parameters ar kotlinlang #getting-started

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dephinera

03/01/2021, 9:21 AM

I'm dealing with function overloading when the parameters are lambdas and stumbled upon the following case:

fun foo(block: String.(String) -> Unit) {

}

fun foo(block: () -> Unit) {

}

fun main() {
    foo { it: String ->
        // calls foo(block: String.(String) -> Unit)
    }
    
    foo { // ERROR
        // how to call foo(block: () -> Unit)
    }
}

Basically is there a way to specify in the second case that I want to call

foo(block: () -> Unit)

. When I specified the type of the lambda argument, it seemed that the compiler was able to figure it out, however

it: Unit

doesn't work for the second case.

Shawn

03/01/2021, 10:30 AM

I don’t think I’ve ever actually read documentation that discusses this particular syntactic construction, but try calling the second function like this:

foo { ->
  // do stuff here
}

➕ 1

this explicitly declares that this lambda takes no parameters, disambiguating the function call

dephinera

03/01/2021, 10:31 AM

okay, that worked. Thanks!

👍 2

Youssef Shoaib [MOD]

03/01/2021, 10:45 AM

I've literally never seen that syntax before wow. This really should be documented

👍 4

Apparently this is part of the official grammar:

lambdaLiteral (used by annotatedLambda, functionLiteral)

: '{' statements '}'

| '{' lambdaParameters? '->' statements '}'

;

that question mark means 0 or 1 of the item, and lambdaParameters defines the whole list of parameters, and so according to the grammar you can have no parameters but still use the

->

before your statements. So I guess it is documented and expected behaviour, it's just that no one actually mentions it anywhere outside of the grammar!

➕ 1

😮 1

dephinera

03/01/2021, 11:28 AM

I admit it, it didn't even occur to me to look for the grammar. Thanks!

Adam Powell

03/01/2021, 3:14 PM

It's kind of neat that you can do this, but wouldn't it be clearer for a reader of the code if these functions had different names instead? If the caller is trying to make a conscious choice of which one is being invoked, are their purposes not different?

☝️ 1

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