Re: Implicit conversion of iterator to reverse_iterator

From:
peter koch <peter.koch.larsen@gmail.com>
Newsgroups:
comp.lang.c++
Date:
30 Apr 2007 11:33:28 -0700
Message-ID:
<1177958008.577959.281070@c35g2000hsg.googlegroups.com>
On 30 Apr., 16:03, dasjotre <dasjo...@googlemail.com> wrote:

On 30 Apr, 10:27, bb <muralibal...@gmail.com> wrote:

Hi,
Please could you clarify why 'implicit conversion' does not take place
while assigning an iterator to reverse_iterator. However, it happens
while initializing/constructing.

e.g.

typedef std::map<int, std::string> MIS;
MIS m1;

// populating m1

MIS::iterator it = m1.lower_bound(4);

// checking the validity of 'it' etc.

MIS::reverse_iterator rit1(it); // implicit conversion takes place
as expected


this is explicit constructor call.

if implicit conversion was allowed
what would you expect compiler to
do with:

for_each(m1.begin(), m1.end(), do_something());
// followed by
for_each(m1.rbegin(), m1.rend(), do_something());

how woudl you expect for_each to make distinction
between reverse_iterator and iterator?


I do not see the problem here. An iterator is not a reverse iterator,
and both functions would be "perfect fits". What could be dangerous
would be to mix iterators and reverse_iterators, but in templated code
where no implicit conversions are made, I see no problems.

/Peter

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