Inspecting lambda parameters

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On Saturday, 10 May 2014 at 10:56:57 UTC, Jacob Carlborg wrote:
> I know that there are templates to inspect function parameters, 
> like ParameterIdentifierTuple and ParameterTypeTuple. But these 
> don't work for templated/untyped lambdas, they're apparently 
> not callables. I don't expect ParameterTypeTuple to work, but 
> it would be nice if ParameterIdentifierTuple and "arity" worked.
>
> Here's an example for clarify:
>
> void foo (alias func) ()
> {
>     alias Types = ParameterTypeTuple!(func);
> }
>
> void main ()
> {
>     foo!(x => x * 2);
> }
>
> Anyone know if this is fixable or if there's a workaround? I 
> would like to avoid using hacks like .stringof. I know there's 
> __parameters as well, but that doesn't work either.

Wasn't there recently a pull request to add TemplateArgsOf, or 
something like that. Also, if you know what type the lambda is 
going to be instantiated with, you can turn it into a function by 
doing:

void foo (alias func) ()
{
     alias Types = ParameterTypeTuple!(func!int);
}