Bug 9886 – Cannot pass .tupleof directly to a template

template Templ(T...) { alias Templ = T; } struct S { int x, y; } void main() { S s; auto tup = s.tupleof; auto x = Templ!(tup); // ok auto y = Templ!(s.tupleof); // ng } For a use-case, a recently created 'reverse' function for the Phobos Tuple type had this implementation: @property auto reversed() { static if (is(typeof(this) : Tuple!A, A...)) alias RevTypes = Reverse!A; Tuple!RevTypes result; auto tup = this.tupleof; // can't call Reverse(this.tupleof) directly result.tupleof = Reverse!tup; return result; }

(In reply to comment #0) > template Templ(T...) { alias Templ = T; } > > struct S { int x, y; } > > void main() > { > S s; > auto tup = s.tupleof; > > auto x = Templ!(tup); // ok > auto y = Templ!(s.tupleof); // ng > } This is disallowed by current language spec. `s.tupleof` makes a tuple of expressions (s.x, s.y). But template cannot take runtime evaluated expressions. So it would be rejected. > For a use-case, a recently created 'reverse' function for the Phobos Tuple type > had this implementation: > > @property > auto reversed() > { > static if (is(typeof(this) : Tuple!A, A...)) > alias RevTypes = Reverse!A; > > Tuple!RevTypes result; > auto tup = this.tupleof; // can't call Reverse(this.tupleof) directly > result.tupleof = Reverse!tup; > return result; > } In member function, template can take field variables as symbol. So this works. struct S { int x; string y; auto test() { auto t = Templ!(this.tupleof); // same as Templ!(x, y) pragma(msg, typeof(t)); // (string, int) } }

Yeah I guess it makes sense this would be disallowed, I wrongly interpreted 't.tupleof' to be a set of symbols.