Re: [boost] Filesystem Library: Final version for Formal Review

From: Thomas Witt (witt_at_[hidden])
Date: 2002-09-16 04:13:07

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Dave,

On Sunday 15 September 2002 13:44, David Abrahams wrote:
> From: "Thomas Witt" <witt_at_[hidden]>
>
> Why not just store it in the policies object to begin with, and provide an
> object factory (which takes a path) as many of the examples do?
>
>     make_directory_iterator(char const* path)
>     {
>         dir_it(some_base_object(), dir_it_policies(path));
>     }
>

Because it's the right solution at the wrong place? Seriously I do think that 
using a object factory would just add overhead and provide zero benefit.

Iterator factories are cool if the iterator type is an complex template 
expression that depends on the argument types and the user isn't really 
interested in the type. They can save a lot of error prone typing. Like in

std::for_each(make_transform_iterator(it, AFunctor(),
              make_transform_iterator(itEnd, AFunctor(), ....);

This point is moot with directory_iterator as its type(typedef) is simple and 
known.

For directory iterator the factory function just adds typing.

std::for_each(make_directory_iterator(path),
              make_directory_iterator(), ....);

opposed to

std::for_each(directory_iterator(path),
              directory_iterator(), ....);

- -> no benefit.

for(directory_iterator it(make_directory_iterator(path)),
                       itEnd();
    it != itEnd;
    ++it);

opposed to

for(directory_iterator it(path),
                       itEnd();
    it != itEnd;
    ++it);

- -> the solution directly using ctor is shorter and less cluttered.

- --Thomas
 
- -- 
Dipl.-Ing. Thomas Witt
Institut fuer Verkehrswesen, Eisenbahnbau und -betrieb, Universitaet Hannover
voice: [phone] - 4273, fax: [phone]
http://www.ive.uni-hannover.de
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