Custom String vs D String performance

[Guillaume Piolat via Digitalmars-d-learn]

On Monday, 5 September 2016 at 11:11:23 UTC, Patric wrote:
> I´m playing remaking D functionalities with nogc structs, and 
> to at least match D performance.
> But in this particular case i´m unable to get near D 
> performance.
>  Can someone point me out what i´m doing wrong, or if there is 
> some magic behind the curtains on D strings?
>
> https://dpaste.dzfl.pl/1c981fdc71ac

     string s;
     string a = "testing";
     string b = "another";
     foreach(_ ; 0..max){
	s = a ~ b;
     }

Potentially this makes no allocation at all. "testing" and 
"another" will be in readonly memory, "a ~ b" will be 
constant-folded, and s will get assigned the same slice 
every-time.

Now replace it with std::string in C++ and count the number of 
malloc ;)