Re: [boost] shared_ptr and std::less (was Re: Smart pointer status, directions, thoughts)

From: John Max Skaller (skaller_at_[hidden])
Date: 2001-05-28 19:34:53

Peter Dimov wrote:
> 
> From: "John Max Skaller" <skaller_at_[hidden]>
> 
> > less<> was introduced _solely_ to provide
> > a total ordering on pointers, since < cannot be
> > relied upon to provide one. It is necessary
> > to create STL sets (etc) of pointers.
> 
> Someone that knows the history of C++ better than me may correct me if I'm
> wrong, but I don't believe this is the case.
> 
> The original STL had std::less that was not guaranteed to provide a total
> ordering on pointers. std::less was just a function object wrapper around
> operator<, just like std::plus is a wrapper around operator+.
> 
> std::less was subsequently 'patched' to provide a total ordering because the
> alternative - imposing a total ordering requirement on operator< - was not
> practical.

        You're right. I think I was the one who first 
proposed the patch. :-)
        
        So I should have said that the requirement that the implementor
provide total ordering semantics, using a partial specialisation 
if necessary, was introduced to permit pointers being used in
containers.
The alternative (requiring < to provide a total order on pointers)
was considered too constraining. [E.g. performance issue for DOS]

-- 
John (Max) Skaller, mailto:skaller_at_[hidden]
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