Why is std.algorithm so complicated to use?

[Jonathan M Davis]

On Tuesday, July 10, 2012 08:51:29 Jacob Carlborg wrote:
> On 2012-07-09 22:23, Ali Çehreli wrote:
> > And a quick fix is to make an array first:
> > 
> > auto str = ["foo", "bar"].map!(x => x)().array();
> > 
> > Also note the added () for map, which is needed when compiled with
> > -property.
> 
> If I first have to convert it to an array, then sort and then convert it
> to an array again. Isn't that missing the whole point of ranges.

The problem is that map is lazy, so it can't be a random access range, and 
sort requires a random access range. If map were eager, it would just be 
creating an array anyway. But you don't need to convert it to an array again 
after sorting it. sort returns a SortedRange so that functions such as find can 
know that it's sorted and take advantage of it, but it sorts in place 
(SortedRange is just a wrapper around the range which was passed in and copies 
no data), so once you've called sort on your array, it's sorted. You can just 
ignore the return type if you're not looking to pass it to a function which 
would take advantage of the fact that it's sorted. But since SortedRange 
_isn't_ lazy (it's just a wrapper around the newly sorted original range, 
after all), it's still a random access range and will work with functions 
which require that (unlike map).

You only end up with a range with fewer capabilities than the original when 
the algorithm itself intrinsicly requires it, and that sort of range is 
generally lazy (since it's more efficient that way, and making it non-lazy would 
be equivalent to wrapping it in a call to array anyway).

- Jonathan M Davis