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.

-- 
/Jacob Carlborg

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);
}

On 2014-05-10 18:56, Meta wrote:

> Wasn't there recently a pull request to add TemplateArgsOf, or something
> like that.

There's this pull request [1] that adds a couple of new traits that might help.

> 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);
> }

Unfortunately I don't know the types it's going to be instantiated with. That's part of the introspecting to figure out.

[1] https://github.com/D-Programming-Language/dmd/pull/3515

-- 
/Jacob Carlborg