Isn't using find with retro awkward?

[spir]

On 02/16/2011 06:22 PM, Andrej Mitrovic wrote:
> Poor implementation, but wouldn't this work?:
>
> import std.stdio;
> import std.range;
> import std.array;
>
> auto findBack(alias pred = "a == b", R, E)(R haystack, E needle)
>      if (isBidirectionalRange!R)
> {
>      R result;
>
>      size_t index;
>      auto reversed = retro(haystack);
>      foreach (item; reversed)
>      {
>          index++;
>          if (item == needle)
>              break;
>      }
>
>      while (index)
>      {
>          result ~= reversed.front;
>          reversed.popFront;
>          index--;
>      }
>
>      return retro(result);
> }
>
> void main()
> {
>      auto orig = [5, 1, 2, 3, 4, 5, 1];
>
>      auto result = findBack(orig, 4);
>      assert(array(result) == [4, 5, 1]);
> }

Of course, it would work (I mean the principle, didn't test). But isn't it 
stupid to (1) reconstruct the result by stepping in reversed (2) reverse twice 
to finally provide a forward result ;-)
The issue I see is the typical case find in an array, a list or another kind of 
sequential collection. You wouldn't do that in any case with such collections. 
Don't you find it foolish algorithmically? With a list (*), you would step 
backward, then just return the node/list from there; with an array, ditto and 
just slice from there.

(And note in you case find(orig, 4) returns the same result ;-)

Denis

(*) If singly-linked only, there could be a need for reverse, but actually this 
would rather reveal a poor choice of data structure, non matching the needs.
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