What about putting array.empty in object.d?

[Jonathan M Davis]

On Wednesday, March 21, 2012 20:17:06 Steven Schveighoffer wrote:
> On Wed, 21 Mar 2012 19:56:41 -0400, Jonathan M Davis <jmdavisProg at gmx.com>
> 
> wrote:
> > Except that containers shouldn't provide indexing if it's not efficient.
> > And
> > from what I've seen, it's far too common for programmers to check length
> > == 0,
> > and they end up doing it on stuff like linked lists where it _is_
> > inefficient.
> 
> Wait, if someone provides inefficient length, what makes you think they
> won't provide inefficient indexing?

Both C++'s STL and D's std.container put requirements on the algorithmic 
complexity of various operations. O(n) indexing would violate them, whereas 
they allow O(n) length/size. So, as long as you use standard containers, you 
can rely on the efficiency of indexing but not that of length/size. And I'd 
argue that 3rd party containers which violate those algorithmic requirements 
are generally doing something wrong (possibly with some exceptions for specific 
situations but not in general).

So, as long as you use standard containers, it's a non-issue. And if you're 
dealing with a 3rd party library that doesn't provide appropriate algorithmic 
guarantees for its containers, you should probably rethink using it.

It _is_ true that some languages and libraries are completely idiotic about it 
though (e.g. Java providing a get function to LinkedList which takes an index 
- which would be the equivalent of providing horribly efficient indexing if they 
had operator overloading in Java). Those are broken APIs IMHO though, in which 
case, you must tread carefully. Well-designed libraries _do_ guarantee efficient 
indexing.

- Jonathan M Davis