Rob Stewart wrote:
From: "Reece Dunn" <msclrhd@hotmail.com>
What I am interested in is a comparison between
* I think that data() would be better named "buffer." The
This would go with the renaming you suggest for functions that are the same in the base and implementation classes (hiding issue).
* Should fixed_string support zero-length strings?
You can have zero-length strings in my implementation (this is what fized_string() defaults to). What you *can't* have is a zero-*capacity* string, which is the same as CharT[ 0 ].
* I'm not sure that there's enough value in const_iter_offset()/iter_offset() versus begin()/end() (const and non-const) in the derived class. You eliminate four trivial functions, but you may eliminate opportunities for optimizations. (I'm thinking there may be derived types that have a better way of computing end and that returning the result of adding zero to a pointer is slower than simply returning the pointer.)
This is true. I will probably expand the interface to the four begin/end functions.
* fixed_string doesn't have a const overload of at().
I shall fix this.
Calling fixed_string's at() "at" seems wrong. You should take the tack of requiring a derivate of detail::basic_string_impl to provide uniquely named, implementation functions that basic_string_impl uses to provide the public interface. You could even suggest that such functions be made private with the basic_string_impl specialization made a friend. Your current approach will generate many "hiding" warnings, too.
I will rename the conflicting names.
* fixed_string's at() shouldn't test the length and throw an exception since detail::basic_string_impl::at() does it and detail::basic_string_impl::operator[] calls it.
fixed_string tests against capacity as a measure against [] usage that would cause buffer overflow, e.g. fixed_srting< 5 > str; str[ 10 ] = 'a'; // ok: exception vs char str2[ 5 ]; str[ 10 ] = 'a'; // foobar
* fixed_string::swap() is missing. * detail::basic_string_impl::get_allocator() expects string_type::get_allocator() but that isn't listed in the requirements levied on the derived type and isn't defined in fixed_string.
These are currently missing becase (1) swap requires a deep copy and haven't implemented that yet; (2) allocators are not used by fixed_string (no need to allocate any data) so it is not implemented (I am considering if/how it should be implemented). NOTE: it should compile despite these missing from fixed_string unless you attempt to call those functions.
* I wouldn't expect fixed_string's StringPolicy to govern how to determine the length of a string passed to a mf as a CharT *.
It does not. string_type::length() returns the value of the string held in the class (return a variable value, defer to container, use traits_type, etc.). traits_type::length( const CharT * ) calculates the length of a string passed to it, wher traits_type is a char_triats compatible interface.
* If I kept looking, I'm sure I'd find many more things, but you are more interested in philosophical differences, so I'll stop here. Look at the end of the message for my summary.
I am actually interested in both. The feedback is appreciated and I will use it to improve the code.
I think John's approach is better, only because it does less type indirection. It relies on the more ordinary pvf approach to the core functionality. Otherwise, the two libraries provide the same functionality (or can when complete).
To simplify my design, I could implement basic_string_impl using the policy approach that flex_string uses. The problem with this is that it requires a usage like: flex_string< fixed_string< 10, char > > str; so in order to get the fixed_string< n > syntax, I would need two classes instead of just the one: this was something I was trying to move away from, but the approach I use has several problems: [1] the code is less optimal (7.5k vs 5k on MS VC 7.1) in my approach, due to the indirection used; the flex_string policy approach would allow compilers to aggressively inline. [2] the implementation functions are exposed in the interface; a policy approach would allow the implementation to be hidden because it can be derived from it like flex_string. [3] in my current approach, I can't use typedefs from the StringPolicy in basic_string_impl (they are not defined yet); seperate classes will solve this. There may be others to this list. So I am going to change to the flex_string approach and see what happens :). Regards, Reece _________________________________________________________________ Express yourself with cool new emoticons http://www.msn.co.uk/specials/myemo