[boost] iterator_adaptor docs [was Filesystem Library ...]

From: Beman Dawes (bdawes_at_[hidden])
Date: 2002-09-15 12:50:58

At 05:13 PM 9/14/2002, David Abrahams wrote:

 >> I frankly don't understand the details of this problem. Am I using
 >> iterator_adaptor incorrectly
 >
 >Yes. A class derived from a valid iterator is not a valid iterator unless
 >you add all the appropriate operators. That's why iterator_adaptor<>
 >defines all the operators. Instantiations of iterator_adaptor<> are valid
 >iterators. Derived classes are generally not valid iterators.

I think you should point that out in the documentation.  I just skimmed the 
docs again and there is no indication I could see that it isn't safe to 
derive from iterator_adaptor.

Instead the docs say things like "There is an unlimited number of ways the 
iterator_adaptors class can be used to create iterators" which made me 
think iterator_adaptor performed some magic that made derivation safe.

Since, as Thomas Witt points out, the point of derivation was to add a 
constructor, it would be nice if the docs explained what a user is supposed 
to do when faced with this need.

 > That's why
 >all the examples in the library use type generators instead of 
inheritance.
 >Just follow the formula given by the library docs and you'll be fine.

I can't find any "formula" in the docs for simple iterators that require 
constructors.

The only discussion I found of generators said "The nicest way to package 
the construction of the transform iterator is to create a type generator". 
That seems to imply there are other choices, and that using a generator was 
optional.

--Beman