On Thursday, 15 January 2015 at 19:30:21 UTC, Tobias Pankrath wrote:
> On Thursday, 15 January 2015 at 19:24:16 UTC, Nordlöw wrote:
>> On Thursday, 15 January 2015 at 13:13:57 UTC, Nordlöw wrote:
>>> I just discovered that zip has StoppingPolicy so why does
>>>
>>> auto commonPrefixLength(R...)(R ranges) if (ranges.length == 2)
>>> {
>>>   import std.range: zip;
>>>   return zip!((a, b) => a[0] != b[1])(ranges);
>>> }
>>
>> I did a silly mistake. The correct version is
>>
>> auto commonPrefixLength(S, T)(S a, T b)
>> {
>>    import std.range: zip, StoppingPolicy;
>>    import std.algorithm: countUntil, count;
>>    const hit = zip(a, b).countUntil!(ab => ab[0] != ab[1]);
>>    return hit == -1 ? zip(a, b).count : hit;
>> }
>>
>> This however needs to process zip(a, b) how do I avoid the extra count?
>>
>> If countUntil returned zip(a, b).count upon failure I would have been done...
>
> What's wrong with commonPrefix(..).length?

Only works if all input arguments have length property.

I would have implemented countUntil() to return

    -length

upon failure instead of

    -1
.

Then I could have just returned abs of the return value from commonUntil.

However

auto commonPrefixLengthAlt(S, T)(S a, T b) @safe pure @nogc nothrow
{
    import std.algorithm: commonPrefix, count;
    return commonPrefix(a, b).count;
}


works on dmd git master!

Limited to 2 arguments, though, but I'm find with that for now :)

On Thursday, 15 January 2015 at 20:21:26 UTC, Nordlöw wrote:
> I would have implemented countUntil() to return
>
>     -length
>
> upon failure instead of
>
>     -1
> .
>
> Then I could have just returned abs of the return value from commonUntil.

I wonder if we could add an extra overload to countUntil in Phobos that takes an enum as first argument similar to zip's StoppingPolicy. Something like FailCountPolicy.

On Thursday, 15 January 2015 at 19:30:21 UTC, Tobias Pankrath wrote:
> What's wrong with commonPrefix(..).length?

Ahh, sorry that works too. I'm surprised :)
DMD/Phobos has become really clever at avoiding allocation.

Seems there may be need for both

    commonPrefixCount

and

    commonPrefixLength

depending on whether string auto-decoding is needed or not.