Re: remove_if with a mask

From:

eLVa <elvadrias@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Tue, 8 Jun 2010 10:09:22 -0700 (PDT)

Message-ID:

<a42ff952-2121-4cca-a752-9ec8975b47bd@z10g2000yqb.googlegroups.com>

On 8 juin, 12:55, "Leigh Johnston" <le...@i42.co.uk> wrote:

"eLVa" <elvadr...@gmail.com> wrote in message

news:7e9e2a4e-12d7-40b6-b5b8-f256f2d5ced9@s9g2000yqd.googlegroups.com...

On 8 juin, 12:32, "Leigh Johnston" <le...@i42.co.uk> wrote:

"eLVa" <elvadr...@gmail.com> wrote in message

news:30423859-3460-442a-b6c1-60be74e899bd@a30g2000yqn.googlegroups.com.=

...

On 8 juin, 11:46, "Leigh Johnston" <le...@i42.co.uk> wrote:

"eLVa" <elvadr...@gmail.com> wrote in message

news:a2bfe5f8-9f05-4673-8b76-d04133be51a4@z8g2000yqz.googlegroups.co=

m...

This does not compile ...
I know this is about it being initialized by a temporary variable
returned by mask.begin() ..
Should I directly pass a reference to the iterator to the
constructor
of maskChecker rather than the vector itself ?

Yes, assign the result of begin() to a variable and pass the variab=

to
the
constructor (by reference). However I mentioned else-thread that
using a
reference wrapper is probably a superior solution.
std::tr1::ref(predicate).

/Leigh

I can't seem to find your post. I tried with a std::tr1::ref(pred) b=

it does not compile, complaining about no class template named
'result' in my predicate struct.

Derive your predicate from std::unary_function<Z, bool>

In what would it be superior ??

No need to have a temporary for the reference and predicates are not
copied
about.

Predicates are not copied, so it is only a gain in memory in this
case, right ?

A temporary for the reference is still required, no ? You don't change
the constructor, so the same problem of initialization from .begin()
arises ? Am I right ? not quite sure ..

I got it right with a reference to an iterator, so I'm glad I alread=

have something working :-)

If you use a reference wrapper than you just store an iterator in the
predicate (not a reference):

Ok that was the catch !
Thank you Leigh, I think I got it definitely right now :-)

struct predicate : std::unary_function<int, bool>
{
predicate( std::vector<bool>& v) : i(v.begin()=

) {}

        bool operator()(int) { return *i++; }
        std::vector<bool>::const_iterator i;

};

int main()
{
        std::vector<int> v1;
        std::vector<bool> v2;
        for (int i = 0; i != 10; ++i)
        {
                v1.push_back(i);
                v2.push_back(i % 2 == 0 ? true : true=

);

        }
        v1.erase(std::remove_if(v1.begin(), v1.end(),
std::tr1::ref(predicate(v2))), v1.end());
        std::copy(v1.begin(), v1.end(), std::ostream_iterator<int=
(std::cout, "
"));

}

/Leigh