On Monday, 1 February 2016 at 22:32:26 UTC, Steven Schveighoffer
wrote:
What I wanted essentially was a template constraint that says
"this type has a member named foo, and t.foo is an lvalue"
-Steve
Like this?
template hasLValProperty(T, string property) {
enum hasLValProperty = __traits(compiles, function(ref T x) {
void requireLVal(V)(ref V y) { }
requireLVal(mixin("x." ~ property));
});
}
struct Foo {
int a;
}
struct Bar {
int b() {
return 0; }
}
struct Baz {
ref int c() {
static int _c;
return _c;
}
}
void test(T, string property)() {
import std.stdio;
write(T.stringof, ".", property, " is ");
if(!hasLValProperty!(T, property))
write("NOT ");
writeln("an lvalue");
}
void main() {
import std.stdio;
test!(Foo, "a")();
test!(Foo, "b")();
test!(Bar, "a")();
test!(Bar, "b")();
test!(Baz, "c")();
}
(DPaste: http://dpaste.dzfl.pl/5877cc17ffd2)
