Labels in struct

[Adam D. Ruppe via Digitalmars-d-learn]

You could use a UDA like that, though getting the offset will be 
a bit tricky.


The idea is to use some uda type, even plain string is good 
enough, then use the __traits to find the first appearance of 
that UDA in the object and return that offset.

Keep in mind that the @uda: syntax applies it to ALL following 
members, it isn't really a label, but if we only look at the 
first time it shows up we can kinda pretend it is one.

Here's an example:


struct Foo {
	int b;
	@("label_one"): // offset 4
	int c;
	int d;
	@("label_two"): // offset 12
	int e;
}

// get the offset of the label on a type, see below for usage
size_t offsetOf(T, string label)() {
	foreach(memberName; __traits(allMembers, T)) {
		foreach(attribute; __traits(getAttributes, __traits(getMember, 
T, memberName))) {
			static if(is(typeof(attribute) == string) && attribute == 
label)
				return __traits(getMember, T, memberName).offsetof;
		}
	}

	assert(0, "no such label");
}

void main() {
        // gives what we expect
	pragma(msg, offsetOf!(Foo, "label_one"));
	pragma(msg, offsetOf!(Foo, "label_two"));
}