Type of string literal concatenated with non-immutable char array

[Per Nordlöw]

On Monday, 1 February 2021 at 15:47:33 UTC, Steven Schveighoffer 
wrote:
> "Concatenation always creates a copy of its operands, even if 
> one of the operands is a 0 length array"

Btw, does

     x ~ y ~ z ~ ...

result in a single allocation?