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From: Hyman Rosen <hymie@prolifics.com>
Subject: Re: Wanted: Ada STL.  Reward: Ada's Future
Date: 1999/02/04
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Stephen Leake wrote:
> I thought Matthew just did that, but you haven't answered the question
> "why does the STL allow iteration past the end of the array". This
> bugs me too. Is there a real reason here, or is it an accident of the
> implementation?

STL iterators are analogous to C pointers; one goal of the STL design is to
be able to use C pointers as iterators in any STL algorithm. Given that C
allows a one-past-the-end pointer to an array, it becomes natural to
express
STL ranges as [i,j). This allows an entire array to be spanned, as well as
allowing an empty range to be easily specified.

> Perhaps it is the most general way to define an iterator that points
> to nothing? Certainly if the underlying implementation of a collection
> is an array, this makes sense. But if the underlying implementation is
> a list, then a null pointer makes more sense. Why not make the
> abstraction resemble a null pointer, rather than an out-of-bounds
> index?

Because you don't always want to operate on the entire container, of
course.
STL algorithms take a pair of iterators when they need a range specified,
and
this allows them to work on arbitrary sections of a container. Also, when
an
algorithm requires a bidirectional iterator, you can go back from a
past-the-end
iterator, but not from a null pointer.