boost::lambda::placeholder and more

The C++0x simplify a lot the usage of the lambda expression still, if you are using a compiler that does not support it yet, it useful to know a couple of tricks that could help us in keeping the code more readable.

For instance, using constant_type<>::type could we define constant to be used in our expression, besides, we see here also how to redefine the name for the placeholders:

#include <iostream>
#include <vector>
#include <algorithm>

#include "boost/lambda/lambda.hpp"
#include "boost/lambda/bind.hpp"
#include "boost/function.hpp"

using std::cout;
using std::endl;

namespace
{
  template <typename T, typename Operation>
  void for_all(T& t, Operation op) { std::for_each(t.begin(), t.end(), op); }

  template<typename T>
  void lambdaBoost(const T& t)
  {
    using namespace boost::lambda;

    constant_type<char>::type space = constant(' ');
    boost::lambda::placeholder1_type _;

    boost::function<void(T::value_type)> f = cout << _ << space;
    for_all(t, f);
    cout << endl;
  }

  template<typename T>
  void lambda0x(const T& t)
  {
    auto f = [] (T::value_type x) { cout << x << ' '; } ;
    for_all(t, f);
    cout << endl;
  }
}

void lambda04()
{
  std::vector<int> v;
  for(int i = 0; i < 5; ++i)
    v.push_back(i);

  lambdaBoost(v);
  lambda0x(v);
}

For more information on boost lambda you could read "Beyond the C++ Standard Library: An Introduction to Boost", by Björn Karlsson, an Addison Wesley Professional book.