[Issue 12404] Zip.back is wrong

[d-bugmail at puremagic.com]

https://d.puremagic.com/issues/show_bug.cgi?id=12404



--- Comment #4 from monarchdodra at gmail.com 2014-03-20 04:20:02 PDT ---
(In reply to comment #3)
> (In reply to comment #2)
> 
> > Yeah. I think the best thing to do at this point is to just let it be.
> 
> Really?

As Peter said, fixing it would break this:

`zip("abc", "123").back`

The fix would be silent breakage, because instead of static asserting, we'd be
run-time asserting.

And even then, if the user wrote:
`zip(StoppingPolicy.requireSameLength, "abc", "123").back`

We'd add *yet* more run-time overhead to something that is meant to be fast to
begin with.
And it would *still* not be completely correct, since it isn't an *Error* to
give it ranges with different lengths...

At best, we could Band-Aid it with a message:
//----
"back/popBack will only function correctly on the `requireSameLength` stopping
scheme, and provided the ranges actually do have the same length."
//----

So I'm all ears, but I don't see how we can do much about it at this point.



//---------

Related, opIndex/opSlice has the same issue for "longuest":

import std.range, std.stdio;

void main()
{
    auto a = [1];
    auto b = [1, 2];
    auto c = [1, 2, 3];
    zip(StoppingPolicy.longest, a, b, c)[2];
}

That said, *that's* fixable, but there'd still be a definite run-time overhead.

//--------

My stance is I don't want to waste any more time/effort on something that can't
be fixed.

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