__traits(getAttributes) with string mixin

[Jacob Carlborg]

I have some code looking like this. I don't understand why I can use a 
string mixin together with __traits(getAttributes) when it doesn't work 
if I use the template "getAttributes".

template Tuple (T...)
{
     alias T Tuple;
}

struct Foo
{
     @(3) int a;
}

template getAttributes (alias s)
{
     alias Tuple!(__traits(getAttributes, s)) getAttributes;
}

void main ()
{
     Foo foo;
     writeln(__traits(getAttributes, mixin("foo.a")));

     // Error: variable foo cannot be read at compile time	
     // writeln(getAttributes!(mixin("foo.a")));

     writeln(getAttributes!(foo.a));
     mixin(`writeln(getAttributes!(foo.a));`);
}

-- 
/Jacob Carlborg