Strange exception, with EXTREMELY SIMPLE toString() in a struct

[Marc Schütz via Digitalmars-d-learn]

On Monday, 7 December 2015 at 08:17:27 UTC, Enjoys Math wrote:
> Exception Message:
> First-chance exception: std.format.FormatException Unterminated 
> format specifier: "%" at 
> C:\D\dmd2\windows\bin\..\..\src\phobos\std\format.d(828)
>
> [CODE]
> module set;
> import std.conv;
>
> struct Set(T) {
> 	string toString() const {
> 		auto str = "{";
> 		return str;
> 	}
> }
>
> unittest {
> 	import std.stdio;
> 	auto A = Set!int();
> 	writeln(A);
> }
> [/CODE]

Works fine for me (Linux x86_64, DMD 2.069). Which version are 
you using exactly? Also, are you sure you're not accidentally 
running an outdated executable, or your executable doesn't 
actually match the code you posted? It doesn't invoke format at 
all.