improving the join function

[Justin Johansson]

On 12/10/2010 11:33 AM, Andrei Alexandrescu wrote:
> I'm looking at http://d.puremagic.com/issues/show_bug.cgi?id=3313 and
> that got me looking at std.string.join, which currently has the sig:
>
> string join(in string[] words, string sep);
>
> A narrow fix:
>
> Char[] join(Char)(in Char[][] words, in Char[] sep)
> if (isSomeChar!Char);
>
> I think it's reasonable to assume that people would want to join things
> that aren't necessarily arrays of characters, so T could be pretty much
> any type. An obvious step towards generalization is:
>
> T[] join(T)(in T[][] items, T[] sep);
>
> But join doesn't really need random access for words - really, an input
> range should suffice. So a generally useful join, almost worth putting
> in std.algorithm, would be:
>
> ElementType!R1[] join(R1, R2)(R1 items, R2 sep)
> if (isInputRange!R1 && isForwardRange!R2
> && is(ElementType!R2 : ElementType!R1);
>
> Notice how the separator must be a forward range because it gets spanned
> multiple times, whereas the items need only be an input range as they
> are spanned once. This is at the same time a very general and very
> precise interface.
>
> One thing is still bothering me: the array output type. Why would the
> "default" output range be an array? What can be done to make join() at
> the same time a general function and also one that works for strings the
> way the old join did? For example, if I want to join things into an
> already-existing buffer, or if I want to write them straight to a file,
> there's no way to do so without having an array allocation in the loop.
> I have a couple of ideas but I wouldn't want to bias yours.
>
> I also have a question from people who dislike Phobos. Was there a point
> in the changes of signature above where you threw your hands thinking,
> "do the darn string version already and cut all that crap!"?
>
>
> Thanks,
>
> Andrei

Yes, "do the darn string version already and cut all that crap".

This is probably the thing to do to make for familiarity among
library users [of other languages].

However, if you have an urge to back-end the implementation
of the colloquial "join" by your ideas, do not give up your
dream.  So long as it is implemented as your private dream
no one will notice and you will remain internally satisfied. :-)

- JJ