findSkip signature

[Graham St Jack]

On 18/01/11 08:04, Andrei Alexandrescu wrote:
> On 1/17/11 3:21 PM, Ali Çehreli wrote:
>> Andrei Alexandrescu wrote:
>>> I just added a useful function to Phobos: findSkip. Refer to
>>>
>>> http://d-programming-language.org/cutting-edge/phobos/std_algorithm.html#findSkip 
>>>
>>>
>>>
>>> and
>>>
>>> http://www.dsource.org/projects/phobos/changeset/2339
>>>
>>> I'm unsure about the signature. Currently the function returns
>>> Tuple!(R1, "balance", bool, "found"), i.e. the balance of the range
>>> being searched and a Boolean telling whether or not the other range
>>> was found. The Boolean is necessary because returning an empty range
>>> is ambiguous - did you find the needle at the very end of the
>>> haystack, or not at all?
>>>
>>> I think a signature that's easier to use is:
>>>
>>> bool findSkip(alias pred = "a == b", R1, R2)(ref R1 haystack, R2 
>>> needle);
>>>
>>> i.e. the haystack is passed by reference and modified if the find was
>>> successful. This is in keep with skipOver's signature, but not in keep
>>> with find's signature.
>>>
>>> Opinions?
>>>
>>>
>>> Andrei
>>
>> I am not sure where findSkip is useful but can we assume that the caller
>> is not interested in whether it was found or not?
>>
>> If the callers are interested, they should have the option of calling
>> find and skip separately. If they are always interested, then find and
>> skip should not be merged together.
>
> findSkip is useful in parsing. One simple case in which it was useful 
> was count() that counts how many times a forward range occurs in 
> another. You can't do that with find(). (Try it!)
>
> I made the executive decision to pass by reference and return a bool.
vote++
>
> http://d-programming-language.org/cutting-edge/phobos/std_algorithm.html#findSkip 
>
>
>
> Andrei
>

-- 
Graham St Jack