Re: [Boost-users] [range] questions about documentation and usage

Subject: Re: [Boost-users] [range] questions about documentation and usage
From: Oswin Krause (Oswin.Krause_at_[hidden])
Date: 2012-11-04 16:01:23

Hi,

> looking through http://en.cppreference.com/w/cpp/concept
> it seems that swappable/valueswappable is a very unusual
> and perhaps even unique case.  I suspect this would be for
> the same reason that boost::begin(A) as a required expression
> raised a red flag when I looked at it. This technique/practice
> creates a concept which I can't easily verify.  A couple of
> other points.
>
> a) I don't think it (boost::begin()) is necessary to implement
> the library.
Why do you think that? in fact the implementation using free standing 
begin() and end() functions as a mean for adapting third party 
containers was deemed so necessary that the standard commitee 
implemented the c++11 range based for in terms of begin(v) and end(v) 
and not in v.begin() and v.end(). Think about that: adding the required 
specialisation of boost::begin() and boost::end() at one central point 
of the program is much easier than writing a wrapper for every such 
container and use that everywhere where boost.range is used in 
conjunction with the container.

> b) I don't find any mention of boost::begin() anywhere in the table
> of contents of the documentation.  I guess it might be implemented
> somewhere for some types like stl containers
> (extending the library Method 1: refers to begin() member
> functions of a user type to be supported - but that would be
> a different thing)
The default implementation of begin(v) is just "return v.begin();" so 
it is not a different thing.

Greetings,
Oswin