Re: [boost] lamda question

From: Joe Van Dyk (joevandyk_at_[hidden])
Date: 2006-07-28 14:42:22

On 7/28/06, Michael Nicolella <boost_at_[hidden]> wrote:
> Because you're passing a function pointer to bind() - but you didn't say
> which version of print_template you want to pass... I think you run into the
> same ambiguity with overloaded functions.

Yes, doing

for_each(v.begin(), v.end(), bind(print_template<int>, _1));

did the trick.. Unfortunate that I have to do that though.  I should
really understand templates better.

Joe

> -----Original Message-----
> From: Joe Van Dyk [mailto:joevandyk_at_[hidden]]
> Sent: Friday, July 28, 2006 11:23 AM
> To: boost_at_[hidden]
> Subject: Re: [boost] lamda question
>
> On 7/27/06, Joe Van Dyk <joevandyk_at_[hidden]> wrote:
> > On 7/27/06, Kevin Spinar <spinarkm_at_[hidden]> wrote:
> > > On 7/27/06, Joe Van Dyk <joevandyk_at_[hidden]> wrote:
> > > > I have Boost 1.33.1 installed.  I'm trying to use Boost.Lamda.
> > > >
> > > > I included all the headers mentioned in the documentation as an
> > > > attempt to fix the compile error.
> > > >
> > > > #include <boost/lambda/lambda.hpp>
> > >
> > > [snip unneeded includes]
> > >
> > > #include <algorithm>
> > >
> > > > #include <list>
> > > >
> > > > int main()
> > > > {
> > > >    using namespace std;
> > > >    using boost::lambda;
> > > >
> > > >    list<int> v(10);
> > > >    for_each(v.begin(), v.end(), _1 = 1);
> > > > }
> > > >
> > > >
> > > > % g++ lambda.cpp
> > >
> > > you should compile with -W -Wall -pedantic -ansi at a minimum.
> > >
> > > > lambda.cpp: In function `int main()':
> > > > lambda.cpp:20: error: `_1' undeclared (first use this function)
> > > > lambda.cpp:20: error: (Each undeclared identifier is reported only
> once for
> > > >    each function it appears in.)
> > > >
> > > > Using gcc 3.3.1.
> > >
> > > Consider upgrading to gcc 4.  With gcc 4, I get:
> > >
> > > error: namespace 'boost::lambda' not allowed in using-declaration
> >
> > Ah, thanks.  I needed
> > using namespace boost::lambda;
> >
> > Joe
> >
>
> Another one:
>
> #include <iostream>
> #include <functional>
> #include <list>
> #include <algorithm>
> #include <boost/lambda/lambda.hpp>
> #include <boost/lambda/bind.hpp>
>
> using namespace std;
>
> template<class T> void print_template(const T& value)
> {
>    cout << "value: " << value << endl;
> }
>
> void print(const int& value)
> {
>    cout << "value: " << value << endl;
> }
>
> int main()
> {
>    using namespace boost::lambda;
>
>    list<int> v;
>    v.push_back(3);
>    v.push_back(4);
>    v.push_back(5);
>    for_each(v.begin(), v.end(), bind(print, _1));  // Works
>
>    // Why doesn't this work?
>    // for_each(v.begin(), v.end(), bind(print_template, _1));
> }
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