Re: [boost] boost CVS changes

From: David Abrahams (abrahams_at_[hidden])
Date: 2001-06-07 13:25:02

----- Original Message -----
From: "John E. Potter" <jpotter_at_[hidden]>
>
> > The question remains, however: what is the type of t?
>
> Anything which may be used in the expression *a = t.  There could be
> many different types.  You don't want me writing
> my_cute_ostream_iterator with operator= for char, int, and double?

I don't want to disallow it, but I don't think it's worth sacrificing
value_type on that altar. We could make the same argument about
InputIterator, I think. The return of operator* is only required to be
convertible to T, so proxies are allowed.

> Note that for ostream_iterator<int> it, *it = 5, *it = 'X', *it = 3.14
> are equally valid.

Erf. What's the point of the template parameter, then? Oh, you mean that the
expressions are valid because int converts implicitly from char and
double... a red herring, no?

> My_cute_ostream_iterator would produce nicer
> results.

Sure.

> I once wanted the value_type of an output iterator in an algorithm,
> but knowing what the algorithm did and the value_type of the
> input iterator allowed me to declare a local of an appropriate
> type.  It might not be the same as the output iterator, but the
> assignment would work.

Suppose I hand you an OutputIterator and an istream and ask you to read
values out of the stream and put them into the OutputIterator...