Re: [Boost-users] boost::range RangeConcept problem.

16 Jan 2013

      Hi Hurcan,

2013/1/16 Hurcan Solter 
...
The following snippet is the mock-up of the problem I am having in order
to be able to reproduce.
--------------------------------------------------------------------------------
#include <iostream>
#include 
#include 
#include 
#include 
#include 
using namespace boost::assign;
struct wxSize
{
    wxSize(int height=0,int width=0):m_height(height),m_width(width)
    { }
    int GetWidth() const {return m_width;}
    int m_height;
    int m_width;
};
class wxWindowBase
{
public:
    wxSize GetTextExtent(const std::string val)
    {
        return wxSize(0,val.length());
    }
    void DoLayout(std::vectorstd::string m_FilteredItems)
    {
using boost::adaptors::transformed;
        wxSize longest = *boost::max_element(m_FilteredItems |
transformed(boost::bind(&wxWindowBase::GetTextExtent,this,_1)),
boost::bind(std::less<int>(),boost::bind(&wxSize::GetWidth,_1),boost::bind(&wxSize::GetWidth,_2)));
std::cout <std::string input;
    input += "o","two","threexxx","four";
    wxWindowBase window;
    window.DoLayout(input);
}
-----------------------------------------------------------------------------------------
The above code fails to compile on GCC4.7.2 and MSVC10 although
it compiles and runs fine on clang3.3
From what I understand ,transformed returns a Single Pass Range and
max_element expects a ForwardRange
and that's the gist of the problem.But it works for something like
max_element(someint_vector |
transformed(doubleit()),std::less<int>()); without problems.
Is there a elegant way to achieve what I am trying to without using a
intermediate container?
Thanks in advance..
This problem's some solution:

1. Don't use member function version `bind` in `transformed`.
the `bind`'s result functor is not DefaultConstructible.
An iterator holding such a functor can't conform to even Input Iterator.
(`max_element` need default construct operation for iterator.)

2. Use `regular` function.
`regular` function is Boost.Range extension library's feature.
`regular` function is convert functor to DefaultConstructible and
CopyAssignable.

http://dl.dropbox.com/u/1682460/git/OvenToBoost/libs/range/doc/html/range_ex...
http://dl.dropbox.com/u/1682460/git/OvenToBoost/libs/range/doc/html/range_ex...

#include 

wxSize longest = *boost::max_element(m_FilteredItems |+
transformed(boost::bind(&wxWindowBase::GetTextExtent,this,_1)),

boost::bind(std::less<int>(),boost::bind(&wxSize::GetWidth,_1),boost::bind(&wxSize::GetWidth,_2)));

You can get here:
https://github.com/faithandbrave/OvenToBoost

This extension is now reviewing by Boost.Range developers.

Thanks,
Akira
...
...
========================
Akira Takahashi
mailto:faithandbrave@gmail.com
https://sites.google.com/site/faithandbrave/about/en