Bug 11606 – Cannot instantiate Tuple of non printable

//---- import std.typecons; class Foo{} void main() { Tuple!(immutable(Foo)) a; } //---- src\phobos\std\format.d(2619): Error: template instance formatObject!(Appender!string, immutable(Foo), char) does not match template declaration formatObject(Writer, T, Char)(ref Writer w, ref T val, ref FormatSpec!Char f) if (hasToString!(T, Char)) src\phobos\std\format.d(2382): Error: template instance std.format.formatValue!(Appender!string, immutable(Foo), char) error instantiating src\phobos\std\typecons.d(570): instantiated from here: formatElement!(Appender!string, immutable(Foo), char) //---- This is problematic, in the sense that we never even made a call to print. We just declared the tuple. Root issue: https://d.puremagic.com/issues/show_bug.cgi?id=11605 Workaround: Make toString() implementation conditional: https://github.com/D-Programming-Language/phobos/pull/1724