• FoxyBrown (1/1) Jul 13 2017 Anyone have an efficient implementation that is easy to use?
• Moritz Maxeiner (31/32) Jul 13 2017 Not sure what you mean by efficient here, but a \theta(n+m) one
• Nicholas Wilson (3/4) Jul 13 2017 If you are OK with just a range spanning the two or more strings,

FoxyBrown <Foxy Brown.IPT> writes:

Anyone have an efficient implementation that is easy to use?

Moritz Maxeiner <moritz ucworks.org> writes:

On Friday, 14 July 2017 at 00:40:38 UTC, FoxyBrown wrote:
 Anyone have an efficient implementation that is easy to use?

Not sure what you mean by efficient here, but a \theta(n+m) one 
is done idiomatically with Allocator+ranges like this (note that 
the casts to and from ubyte are necessary, because 
std.range.primitives.hasLength returns false for narrow strings, 
so we have to explicitly state that we want to work in code 
units):

---
char[] strcat(Allocator)(Allocator alloc, string a, string b)
{
	import std.experimental.allocator : makeArray;
	import std.range : chain;
	return cast(char[]) alloc.makeArray!ubyte(chain(cast(ubyte[]) a, 
cast(ubyte[]) b));
}
---

Usage example:
---
void main(string[] args)
{
	import std.stdio;

	import std.exception : enforce;
	enforce(args.length == 3);

	import std.experimental.allocator : dispose;
	import std.experimental.allocator.mallocator;
	alias alloc = Mallocator.instance;

	char[] concated = alloc.strcat(args[1], args[2]);
	scope (exit) alloc.dispose(concated);

	writeln(cast(string) concated);
}
---

Nicholas Wilson <iamthewilsonator hotmail.com> writes:

On Friday, 14 July 2017 at 00:40:38 UTC, FoxyBrown wrote:
 Anyone have an efficient implementation that is easy to use?

If you are OK with just a range spanning the two or more strings, 
then you could use chain as is.