Bug 9426 – [enh] polymorphic lambda should be aliasable

I don't see a compelling reason why we should disallow assigning polymorphic lambdas to manifest constants. This would allow the following code to work. enum foo = bar => bar * 2; foo(10); foo!uint(10); // probably too The equivalent template would be. template foo(T) { auto foo(T bar) { return bar * 2; } } This is for example very handy to replace C-style macros. #define MASK(val) ((val) & 0xF) vs. enum MASK = val => val & 0xF; related: Bug 7176, Bug 8452

This would mean 'enum' variable could refer to templates... I don't think this is a good idea, enums are for values. Alternative: alias foo = bar => bar * 2; foo(10); foo!uint(10); // probably too This fits much better with the existing lanuage IMO.

(In reply to comment #1) > This fits much better with the existing lanuage IMO. You are right.

Now the D language supports enum and alias used as lambdas, so adding template function lambdas seems good: import std.typecons: Tuple; void main() { alias Pair(T) = Tuple!(T, T); // OK auto p = Pair!int(10, 20); enum isGood(T) = is(T == int) || is(T == long); // OK static assert(isGood!int); enum foo(T) = (T x) => x * x; // OK static assert(foo!int(5) == 25); alias bar = x => x * x; // Error }

*** This issue has been marked as a duplicate of issue 12421 ***