What is the simplest way of doing @nogc string concatenation?

[Guillaume Piolat via Digitalmars-d-learn]

On Thursday, 3 November 2016 at 18:54:14 UTC, Gary Willoughby 
wrote:
> What is the simplest way of doing @nogc string concatenation?

I use sprintf + zero-terminated strings (or a RAII struct to 
convert slices to ZT strings).