[Issue 11012] [TDPL] is(typeof(f) == function) fails with some functions

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=11012

ZombineDev <petar.p.kirov at gmail.com> changed:

           What    |Removed                     |Added
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                 CC|                            |petar.p.kirov at gmail.com

--- Comment #5 from ZombineDev <petar.p.kirov at gmail.com> ---
(In reply to Alexander from comment #3)
> static assert(is(typeof( (){} ) == function));	// fails as well
> 
> This issue doesn't allow to get lambda parameter types tuple, and this
> blocks my development. I'll try to have a look at the dmd source.

Is the blocking issue that in code similar to the following, there's an error
on line 11:

---
import std.traits;

pragma (msg, ReturnType!( (){} )); // void
pragma (msg, Parameters!( (){} )); // ()

pragma (msg, ReturnType!( (int x, double y) => "test" )); // string
pragma (msg, Parameters!( (int x, double y) => "test" )); // (int, double)

void lambdaTypeWithParameter(alias lambda, Param)(Param p)
{
    pragma (msg, Parameters!(lambda)); // line 11 - doesn't compile

    alias RT = typeof(lambda(p));

    pragma (msg, RT); // line 15
}

void main()
{
    lambdaTypeWithParameter!(x => "test2")(true); // line 15 -> string
    lambdaTypeWithParameter!(x => x)(2);          // line 15 -> int
    lambdaTypeWithParameter!(x => 3.0 * x)(2);    // line 15 -> double
}
---

?

If that's the case, the error is expected since the lambda in that context is
polymorphic - an un-instantiated function template meaning that its parameters
are not bound to a specific type.

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