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

[gdr at integrable-solutions dot net]

------- Additional Comments From gdr at integrable-solutions dot net  2005-07-24 17:18 -------
Subject: Re:  partial_sum is too constrained

"squell at alumina dot nl" <gcc-bugzilla@gcc.gnu.org> writes:

| ------- 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,

Oh, the standard is quite explicit about that.  Look up the
requirement table input iterators and compare it with other iterators.

| but isn't
| that requirement implied in the semantics for '*r++'?

No.

| 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)

No, that is issue is different.  I'm talking about the
copy-construction of the iterator itself; you're talking about the
copy-construction of the value_type.  Not the same thing.

| > 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?

It should probably be a separate one.  Thanks!

-- Gaby


-- 


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