DMD 2.054:


import std.typecons;
Tuple!(int, "x") foo() pure {
    int y1 = foo().x;
    int y2 = foo()[0];
    return typeof(return)(0);
}
void main() {}


test.d(3): Error: pure nested function 'foo' cannot access mutable data '_field_field_0'
test.d(4): Error: no [] operator overload for type Tuple!(int,"x")