Traits and UDAs

[Chris Williams]

I decided to write up a little application to test using User 
Defined Attributes and have one question. Here is a working 
application that allows me to mark certain members of a function 
to be dumped:

import std.stdio;

enum Dump = "Dump";
template Dumper(T) {
	void dump() {
		foreach (mem; __traits(allMembers, T)) {
			auto attributes = __traits(getAttributes, __traits(getMember, 
T, mem));
			static if ( attributes.length > 0 && __traits(getAttributes, 
__traits(getMember, T, mem))[0] == Dump ) {
				writeln(mem);
			}
		}
	}
}

class Foo {
	@Dump int hello;
	
	@Dump int world;
	
	int bye;
	
	mixin Dumper!(Foo);
}

int main(string[] args) {
	Foo f = new Foo();
	f.dump();
	
	return 0;
}


The eighth line bothers me, though. It seems like I should be 
able to write:

if (attributes.length > 0 && attributes[0] == Dump)

However, that fails to compile with the message:

test.d(7): Error: variable _attributes_field_0 cannot be read at 
compile time
test.d(8): Error: expression !!(_attributes_field_0 == "Dump") is 
not constant or does not evaluate to a bool
test.d(7): Error: variable _attributes_field_0 cannot be read at 
compile time
test.d(8): Error: expression !!(_attributes_field_0 == "Dump") is 
not constant or does not evaluate to a bool

Any thoughts?