Re: [boost] [string_algo] comments

From: Pavol Droba (droba_at_[hidden])
Date: 2006-10-31 05:21:54

Hi,

I'll try to respond, but I will need more time for it. Please be patient.

Regards,
Pavol.

Martin Adrian wrote:
> I have used the string_algo library for a long time and is used to how it works.
> Recently I had to introduce a collegue to it and started to write a document but
> it wasn't easy. 
> 
> Here is a few points:
> 
> 1. The word predicate is used to describe anything which can return a boolean
> value. While this is technicly correct it creates confusion since there are many
> different predicates used in the library.
> Example: Both trim_if and starts_with takes a PredicateT argument but they are
> not the same predicate types.
> 
> I have found the following predicates:
> - Unary token predicate:
> These are all the classification predicates: is_space, is_from_range etc
> - Binary token predicate:
> These are the token comparison predicates: is_equal, is_iless etc
> - Unary string predicate:
> These are the string validation predicates: all, regex_match
> - Binary string predicate:
> These are the substring match predicates: starts_with, contains etc.
> 
> Note here that the "string predicates" are different from the "token predicates"
> since they don't return functors (and can't be used directly with standard
> algorithms).
> 
> My suggestion is to clear this up in such a way that all predicate types are
> given a name (e.g. UnaryTokenPredicateT) and that they are available as both a
> free function and a boolean functor. Naming will be tricky to get right.
> 
> is_space:
> functor: boost::is_space( Locale )
> free function: std::is_space( Char, Locale )
> is_iequal:
> functor: boost::is_iequal( Locale )
> free function: ??(Char1, Char2, Locale)
> starts_with:
> functor: ??(String, String)
> free function: starts_with(String, String)
> 
> 2. There are a number of suffixes used within the library. Here is my
> interpretation:
> 
> nosuffix: Mutable verision
> _copy: const version returning a copy
> _if: version using a (non-default) predicate
> _regex: version using a regex predicate
> _first, _last, _nth, _all, _head, _tail: for search/replace/erase algorithms
> _range: Not sure what this is supposed to mean
> 
> Most are fine but there are some inconsistances:
> - find/replace/erase algorithms can work with 2 different predicates (token
> predicate and Finder). The naming isn't consistant.
> find_all takes a token predicate while make_find_iterator uses a Finder.
> - trim taking a unary token predicate is called trim_if but find taking the same
> argument is called find_token
> - replace with predicate is called find_format
> - join taking a regex argument is called join_if
> - starts_with etc use overload instead of _if suffix
> 
> 3. There are lot of (randomly) missing algorithms.
> - erase_if, erase_all_if, erase_copy_if, erase_all_copy_if taking a Finder
> argument (all these are availble as replace with _formatter suffix)
> - is_token, is_itoken, is_ianyof
> - ifirst_finder, ilast_finder, inth_finder
> - find_all and split taking a finder argument
> - make_split_iterator and make_find_iterator with token predicate
>  
> 4. Other stuff
> - ilexicographical_compare is missing locale argument
> - range_finder seems odd. What is the purpose?
> - why is the predicate called not_greater instead of less_equal (compare to
> std::less_equal)
> - regex_search_result is derived from iterator_range but iterator_range doesn't
> have a virtual destructor. It might be safe but I couldn't verify it.
> - there is no special string_algo "regex_match" predicate. The regex version is
> limited to basic_string argument.
> 
> 
> 
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