Re: Isn't using find with retro awkward?

[spir]

On 02/15/2011 05:03 AM, Jonathan M Davis wrote:
On Monday 14 February 2011 19:35:21 Andrej Mitrovic wrote:
import std.stdio, std.algorithm, std.range;
void main()
{
     writeln( find([5, 1, 2, 3, 4, 5, 1], 5) );
     writeln( find(retro([5, 1, 2, 3, 4, 5, 1]), 5) );
}

Output:
[5, 1, 2, 3, 4, 5, 1]
[5, 4, 3, 2, 1, 5]

The docs for find are:
"returns : haystack advanced such that binaryFun!pred(haystack.front,
needle) is true " "To find the last occurence of needle in haystack, call
find(retro(haystack), needle). "

To me, if I was looking for the last element in a range I would expect to
get a range with the found element followed by an elements after it.
Obviously retro reverses the range (it just hard-wires front=back,
back=front for those not in the know), so this code is correct.

Still, I would expect that finding a last element in this range:
[5, 1, 2, 3, 4, 5, 1]

would return the range:
[5, 1]

and not:
[5, 4, 3, 2, 1, 5]

Isn't that what most people would want when they're looking for the last
matching element?

retro revereses the whole range. What you want is something like findFromBack. 
Of
course, retro isn't going to be what you want (though I guess I can understand
why you would think that it would work if you didn't think it through).

I don't think that we have any functions like findFromBack though. It's probably
worth an enhancement request.

Indeed. The code just does what it says. I also understand Andrej's point. But 
it's a different feature; and one worth inclusion in Phobos, as Jonathan says.
Note: there is a mental trap here ;-) <iterating in reverse order !is reversing 
the array and iterating>

Denis
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