Bug 15737 – forward reference error in std.format

struct S { Object ca; void foo() const { import std.stdio; writeln(this); } } causes this error: /Users/john/Git/phobos/std/format.d(2912): Error: template instance std.format.formatObject!(LockingTextWriter, const(Object), char) does not match template declaration formatObject(Writer, T, Char)(ref Writer w, ref T val, ref FormatSpec!Char f) if (hasToString!(T, Char)) /Users/john/Git/phobos/std/format.d(2645): Error: template instance std.format.formatValue!(LockingTextWriter, const(Object), char) error instantiating /Users/john/Git/phobos/std/format.d(3164): instantiated from here: formatElement!(LockingTextWriter, const(Object), char) /Users/john/Git/phobos/std/format.d(3477): instantiated from here: formatValue!(LockingTextWriter, const(S), char) /Users/john/Git/phobos/std/format.d(467): instantiated from here: formatGeneric!(LockingTextWriter, const(S), char) /Users/john/Git/phobos/std/stdio.d(1298): ... (1 instantiations, -v to show) ... /Users/john/Git/phobos/std/stdio.d(3095): instantiated from here: write!(const(S), char) test.d(8): instantiated from here: writeln!(const(S)) /Users/john/Git/phobos/std/format.d(470): Error: forward reference to inferred return type of function call (ref arg) { return cast(const(void*))&arg; } (_param_2) /Users/john/Git/phobos/std/format.d(546): Error: template instance std.format.formatNth!(LockingTextWriter, char, const(S)) error instantiating /Users/john/Git/phobos/std/stdio.d(1298): instantiated from here: formattedWrite!(LockingTextWriter, char, const(S)) /Users/john/Git/phobos/std/stdio.d(3095): instantiated from here: write!(const(S), char) test.d(8): instantiated from here: writeln!(const(S))

The problem is that the function has the const identifier which implicitly makes this const, while writeln expects a non-const argument. I think that this isn't an issue, but a programming mistake; removing const from the functions will solve the issue.

Simpler example with the same problem: void main() { import std.stdio; const Object o; writeln(o); } Not using const is a workaround, but a) writeln should be able to work with a const Object and b) even if it can't, it shouldn't cause a forward reference error.

I just tested that with DMD v2.081.2, both of the mentioned examples now compile and run without errors. This issue is thus fixed.