@nogc formattedWrite

[Nordlöw]

Is it currently possible to somehow do @nogc formatted output to 
string?

I'm currently using my `pure @nogc nothrow` array-container 
`CopyableArray` as

@safe pure /*TODO nothrow @nogc*/ unittest
{
     import std.format : formattedWrite;
     const x = "42";
     alias A = CopyableArray!(char);
     A a;
     a.formattedWrite!("x : %s")(x);
     assert(a == "x : 42");
}

but I can't tag the unittest as `nothrow @nogc` because of the 
call to `formattedWrite`. Is this because `formattedWrite` 
internally uses the GC for buffer allocations or because it may 
throw?

It would be nice to be able to formatted output in -betterC...