functors with template lambdas

[weaselcat via Digitalmars-d-learn]

On Saturday, 16 May 2015 at 02:04:39 UTC, Vlad Levenfeld wrote:
> I think this code should be allowed, but it isn't:
>
> 	struct Functor (T)
> 	{
> 		T a;
>
> 		auto ref fmap (alias f)()
> 		{
> 			return Functor (f(a));
> 		}
> 	}
>
> 	auto ref identity (T)(auto ref T a)
> 	{
> 		return a;
> 	}
>
> 	void main()
> 	{
> 		Functor!int a;
>
> 		static auto id (T)(T x)
> 		{return x;}
>
> 		a.fmap!identity; // ok
>
> 		a.fmap!id; // ok
>
> 		a.fmap!((int x) => x); // ok
>
> 		a.fmap!(x => x); // Error: template instance fmap!((x) => x) 
> cannot use local '__lambda1' as parameter to non-global 
> template fmap(alias f)()
> 	}
>
> This seems like one of those things that doesn't work because 
> of some compiler implementation detail rather than a 
> consequence of the language rules but I'm not sure. Opinion?

very long standing compiler bug
https://issues.dlang.org/show_bug.cgi?id=3051