Alas the presence of parameter UDAs breaks
std.traits.ParameterDefaults:
import std.traits;
struct attr;
void f(@attr int);
pragma(msg, ParameterDefaults!f.stringof);
Error:
dmd -c bug.d
bug.d(4): Error: undefined identifier `attr`, did you mean
variable `ptr`?
/home/jll/dlang/dmd-2.090.1/linux/bin64/../../src/phobos/std/traits.d(1526):
Error: template instance `std.traits.ParameterDefaults!(f).Get!0LU` error
instantiating
/home/jll/dlang/dmd-2.090.1/linux/bin64/../../src/phobos/std/traits.d(1529):
instantiated from here: `Impl!0LU`
bug.d(6): instantiated from here: `ParameterDefaults!(f)`
bug.d(6): while evaluating `pragma(msg,
ParameterDefaults!(f).stringof)`
I filed a bug report (20744). And examined the code of
ParameterDefaults. I think I understand how it works, for the
most part, but I haven't been able to find a fix yet.
I'd like to understand why taking a slice of __parameters vs
fetching the first element matters. What is the (meta?) type of
__parameters[0..1]? I think I'd need to make a copy of it, minus
the UDAs tucked at the beginning. But I haven't found a way of
splitting it into smaller components. I tried using indexation
and variadic template parameters, but it always collapses into a
string. Makes me think of wave functions in quantum mechanics ;-)
