Generic string join

[JS]

On Monday, 29 July 2013 at 09:01:36 UTC, JS wrote:
> Here is a optimal generic string joiner that maximizes compiler 
> optimization, allows for a variable number of arguments that 
> can be strings or arrays of strings.
>
> http://dpaste.dzfl.pl/0a021e1f
>
> Drawbacks:
>     1. Static if explosion
>     2. Not elegant
>     3. Only works with RT strings or RT string arrays, would be 
> nice to work with chars and possibly others.
>     4. Does not have the ability to use book ends 
> delimitation... not difficult to do but just more bloat-code.
>     5. Would be nice to allow apply a lambda to each "element". 
> Again, not hard but requires all those special cases to deal 
> with proper delimitation due to the recursion required.
>     6. Requires a mixin statement... this is not pretty at all. 
> One can't wrap the mixin in a normal function call because it 
> defeats the purpose of optimization(CT strings will be passed 
> as variables and not optimized by the CT).
>     etc...
>
> While I have some code to flatten such arrays before 
> delimitation, which would probably make it much easier, which 
> is the way I started, the code was going to turn out to be the 
> same in the end as the flattener, so I just modified the 
> code(basically use string concatenation instead of tuple 
> concatenation).
>
>
> Anyways, maybe someone has a good idea how to improve the code 
> to achieve the same results. Note in in the test, every 
> possible 3-combination is tried, which I think is good enough 
> to prove the validity of the code.

BTW, one can wrap the template to remove the mixin in #6 but this 
is not very satisfactory as it has a much higher performance hit 
for CT joining.

template t(T...)
{
	string t(string d, T args)
	{
		return mixin(tJoin!(",", args));
	}
}

mixin(tJoin!(",", "a", "b")) is just 4 instructions max. Using t 
is about 10-15 times that(although I'm not sure if inlining will 
solve that).