commonLength

["Nordlöw" via Digitalmars-d-learn]

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 :)