std.utf.decode @nogc please

[Robert burner Schadek via Digitalmars-d]

lately when working on std.string I run into problems making 
stuff nogc as std.utf.decode is not nogc.

https://issues.dlang.org/show_bug.cgi?id=13458

Also I would like a version of decode that takes the string not 
as ref.

Something like:

bool decode2(S,C)(S str, out C ret, out size_t strSliceIdx)
     if(isSomeString!S && isSomeChar!C) {}

where true is returned if the decode worked and false otherwise.

Ideas, Suggestions ... ? any takers?