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digitalmars.D - findSkip signature

reply Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> writes:
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
Jan 16 2011
parent reply =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
Andrei Alexandrescu wrote:
 I just added a useful function to Phobos: findSkip. Refer to
 
 http://d-programming-language.org/cutting-edge/phobos/std_alg
rithm.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. Ali
Jan 17 2011
parent reply Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> writes:
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. http://d-programming-language.org/cutting-edge/phobos/std_algorithm.html#findSkip Andrei
Jan 17 2011
parent Graham St Jack <Graham.StJack internode.on.net> writes:
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_alg
rithm.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.

 http://d-programming-language.org/cutting-edge/phobos/std_alg
rithm.html#findSkip 



 Andrei

-- Graham St Jack
Jan 17 2011