• Jan =?UTF-8?B?SMO2bmln?= (13/13) Oct 29 2020 I have asked this on StackOverflow[1]. I have received a valid
• rikki cattermole (10/10) Oct 29 2020 (Params){ FunctionBody; }
• Jan =?UTF-8?B?SMO2bmln?= (8/13) Oct 29 2020 This would mean, that this one should work as well.
• Jan =?UTF-8?B?SMO2bmln?= (4/5) Oct 29 2020 It does not work as I intended, as `() => {}` has not the return
• rikki cattermole (10/17) Oct 29 2020 alias RT = void function();
• Paul Backus (8/13) Oct 29 2020 Arrow lambdas take a single *expression* on the right-hand side,
• H. S. Teoh (8/15) Oct 29 2020 What you want is `() {}`, which is equivalent to `void function() {}`.

Jan =?UTF-8?B?SMO2bmln?= <hrominium gmail.com> writes:

I have asked this on StackOverflow[1]. I have received a valid 
answer, which solves my problem, however, I have still not 
understood, why some versions of it work and some don't.

The code is here[2].

I don't understand why `a` compiles just fine, while `b` and `c` 
don't.


I think, that I don't understand what `void function()` does or 
is.
Can someone explain it to me?


And I don't see why `(){}` works and `() => {}` does not.



[1]: 
https://stackoverflow.com/questions/64581514/void-lambda-function/64587101#64587101
[2]: https://run.dlang.io/is/GFe9Ht

rikki cattermole <rikki cattermole.co.nz> writes:

(Params){ FunctionBody; }

Rule: ref|opt ParameterWithMemberAttributes FunctionLiteralBody

https://dlang.org/spec/expression.html#function_literals




void function()

Is a type https://dlang.org/spec/type.html#delegates




() => {}

Is actually:

() => Expression

Rule: ref|opt ParameterWithMemberAttributes => AssignExpression

https://dlang.org/spec/expression.html#lambdas

Jan =?UTF-8?B?SMO2bmln?= <hrominium gmail.com> writes:

On Thursday, 29 October 2020 at 08:48:59 UTC, rikki cattermole 
wrote:
 () => {}

 Is actually:

 () => Expression

 Rule: ref|opt ParameterWithMemberAttributes => AssignExpression

 https://dlang.org/spec/expression.html#lambdas

This would mean, that this one should work as well.
And you can![1]

I have changed line 13 from `F();` to `return F();`.
Why does this help???
This is a little weird.



[1]: https://run.dlang.io/is/eGah5v

Jan =?UTF-8?B?SMO2bmln?= <hrominium gmail.com> writes:

On Thursday, 29 October 2020 at 09:01:12 UTC, Jan Hönig wrote:
 This would mean, that this one should work as well.

It does not work as I intended, as `() => {}` has not the return 
type of `void`.

(I don't know how to print: `ReturnType!(() => {})`)

rikki cattermole <rikki cattermole.co.nz> writes:

On 29/10/2020 10:06 PM, Jan Hönig wrote:
 On Thursday, 29 October 2020 at 09:01:12 UTC, Jan Hönig wrote:
 This would mean, that this one should work as well.

 
 It does not work as I intended, as `() => {}` has not the return type of 
 `void`.
 
 (I don't know how to print: `ReturnType!(() => {})`)

alias RT = void function();
alias Type = RT function();

() => 7;

is equivalent to:

int func() {
	return 7;
}

Or:

() { return 7; }

Paul Backus <snarwin gmail.com> writes:

On Thursday, 29 October 2020 at 09:06:21 UTC, Jan Hönig wrote:
 On Thursday, 29 October 2020 at 09:01:12 UTC, Jan Hönig wrote:
 This would mean, that this one should work as well.

 It does not work as I intended, as `() => {}` has not the 
 return type of `void`.

 (I don't know how to print: `ReturnType!(() => {})`)

Arrow lambdas take a single *expression* on the right-hand side, 
not a function body between curly braces. When you write

     () => {}

the right-hand side is interpreted as an expression, and is 
expanded by the compiler to

     () => function void() {}

I.e., it is a function that returns another function.