[Bug libstdc++/22634] partial_sum is too constrained

["squell at alumina dot nl" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From squell at alumina dot nl  2005-07-24 16:42 -------
(In reply to comment #7)

> Yes, the standard requirements for iterators exhibit inconsistencies
> at many places; for example an InputIterator is not required (by the
> Standard) to be copy-constructible; consequently it cannot be used as
> function parameter type.  

Yes, I noticed the standard isn't explicit about that, but isn't
that requirement implied in the semantics for '*r++'?

I read somewhere the LWG believed the requirement to be implicit.
(found: http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#241)

> BAck to the issue of this PR; I think there is way too vagueness in
> the standard and the "obvious" thing to do is to use the natural type
> of the intermediate results.  However, we may actually want to submit
> a DR (I'll do it).  I would suggest this issue be suspended in the
> meantime.

I agree the paragraph should probably make it explicit what type is being
used. I think there's another subtle error in the Effects clause, since 
dereferencing an input iterator invalidates previous copies, and order of
evaluation is unspecified.

I noticed this also happens in unique_copy. It works on Input Iterators but
its semantics are specified in terms of '*i == *(i-1)' or 'pred(*i, *(i-1))'.

Perhaps this should be part of the DR, or a seperate one?

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22634