On Friday, December 09, 2011 12:44:37 bearophile wrote: > Jonathan M Davis: > > It sounded like you were, > > Right, I was :-) But you have changed my mind when you have explained me > that nothing in std.algorithm is grapheme-aware. So I have reduced the > amount of what I am asking for.
So, now you're asking that char and wchar arrays be reversible with reverse such that their code points are reversed (i.e. the result is the same as if you reversed an array of dchar). Well, I'm not sure that you can actually do that with the same efficiency. I'd have to think about it more. Regardless, the implementation would be _really_ complicated in comparison to how reverse works right now. char[] and wchar[] don't work with reverse, because their elements aren't swappable. So, you can't just swap elements as you iterate in from both ends. You'd have to be moving stuff off into temporaries as you swapped them, because the code point on one side wouldn't necessarily fit where the code point on the other side was, and in the worst case (i.e. all of the code points on one half of the string are multiple code units and all of those on the other side are single code units), you'd pretty much end up having to copy half the array while you waited for enough space to open up on one side to fit the characters from the other side. So, regardless of whether it has the same computational complexity as the current reverse, its memory requirements would be far more. I don't think that the request is completely unreasonable, but also I'm not sure it's acceptable for reverse to change its performance characteristics as much as would be required for it to work with arrays of char or wchar - particularly with regards to how much memory would be required. In general, the performance characteristics of the algorithms in Phobos don't vary much with regards to the type that that's used. I'm pretty sure that in terms of big-o notation, the memory complexity wouldn't match (though I don't recall exactly how big-o notation works with memory rather than computational complexity). - Jonathan M Davis
