Bug 15743 – typeof function literal with unnamed parameter of aliased type is void

alias T = int; pragma(msg, typeof((string){}).stringof); // void pragma(msg, typeof((string s){}).stringof); // void function(string) pragma(msg, typeof((int){}).stringof); // void function(int) pragma(msg, typeof((T){}).stringof); // void I would expect the first pragma to print void function(string), and the last to print void function(int). It appears the issue is with a parameter that has no name _and_ is declared as an aliased type (e.g. if you use immutable(char)* instead of string it works as expected).

In `(string){}` and `(T){}`, `string` and `T` are actually parameter names, not types. The function literals generate function templates like these: void foo(A)(A string) {} void foo(A)(A T) {} And typeof of a template is void. The same does not happen with `(int){}` because you can't have a parameter named "int". So it's taken as a type instead. I'm not sure if there's anything to be fixed/improved here. Maybe function signatures like `void f(int string) {}` should not be allowed ("string" being the name of the parameter here).

Oh, that seems obvious in retrospect. I was confused by a unittest in std/variant: https://github.com/D-Programming-Language/phobos/blob/master/std/variant.d#L2051-2053. !__traits(compiles, ...) passes, but not for the reason I thought! I also assumed string is a keyword, but apparently its not. I think its fair to close this. I have a fix for that test included as part of a PR for something else: https://github.com/D-Programming-Language/phobos/pull/4035.