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From: James Kuyper <kuyper@wizard.net>
Subject: Re: STL and set_union algorithm question? (newbie to STL!)
Date: 1998/04/17
Message-ID: <35376387.41C6@wizard.net>#1/1
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Approved: Fergus Henderson <fjh@cs.mu.oz.au>
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Organization: NASA Goddard Space Flight Center -- Greenbelt, Maryland USA
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> James Kuyper <kuyper@wizard.net> writes:
> 
> > Oleg Zabluda wrote:
> > > 
> > > James Kuyper <kuyper@wizard.net> wrote:
> 
> > > : If a non-const iterator were implementable for set<>, then (*i)=b should
> > > : be the equivalent of erase(i) followed by an insert(b). This would be of
> > > : neglible importance in typical uses of sets, but would allow modifying
> > > : algorithms to be applied to sets without being aware of the special
> > > : characteristics of sets.
> > > 
> > > You can easily provide such an iterator yourself. Call it
> > > replace_iterator<Iterator>. And the corresponding function
> > > replacer(Iterator).
> > > 
> > > Just a thought.
> > 
> > What operator overload do you place the insert() call in?
> 
> Let's call the new iterator 'mutable_set_iterator'.
> 
> You can overload mutable_set_iterator::operator= 
> (const element_type&).
> 
> mutable_set_iterator::operator* can return *this (as 
> in insert_iterator).
> 
> This is technically possible but: 
> - IMO changing set::iterator to mutable_set_iterator 
>   is a bad idea
> - it breaks the iterator requirements (already broken by 
>   insert_iterator, I know)
> 

If you override mutable_set_iterator::operator*() to return *this, then
how do you do the following:

void func(mutable_set_iterator i)
{
	(*i)->member_function();
}

You could make this work by defining set<T>::iterator to be a
mutable_set_iterator derived from T. However, when T is a class type
such as 'long' or 'MyClass *', you cannot derive from it.
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