1.5.4.2 Adaptable

• Four adapter is not1, not2, bind1st and bind2nd. It can change you current functor. An example is below: equal_to is binary function, but count_if only need unary function. bind1st or bind2nd can change binary function to unary function. another function is not1, used for unary function, not2 used for binary function.
  int array[] = {10,20,30,40,50,10}; int cx; 
  cx = count_if (array, array+6, bind1st(equal_to<int>(),10));
• In order to use these four adapters. You functor should be inheriated from unary_funciton or binary_function. It make you function object has typedef information, which not1 or not2 will use them.
• Usage of ptr_fun, If you want to adapter a current function, (not function object), because function doesn’t have any typedef information, so you have to use ptr_fun firstly.
  bool IsBad(Foo& f); 
   
  find_if(vect.begin(), vect.end(), 
    not1(IsBad);  //error! don’t compile; 
   
  find_if(vect.begin(), vect.end(), 
    not1(ptr_fun(IsBad ) ); //OK, now: 
   
  //recommend to use c++11 new feature 
  //  std::not1(std::cref(isvowel))); 
  //  std::not1(std::function<bool(char)>(isvowel)));
• Usage of mem_fun, mem_fun_ref
  list<Foo*> lpf 
  for_each(lpf.begin(),lpf.end(),mem_fun_ref(&Foo::testFun) ); 
   
  list<Foo> lf 
  for_each(lf.begin(),lf.end(),mem_fun(&Foo::testFun) );
• With variadic templates, a lot of general function composing can be expressed much more simply and consistently, so all of the old cruft is no longer necessary: depracated in C++ 11. (but support) Do use: std::function, std::bind, std::mem_fn, std::result_of, lambdas . Don’t use: std::unary_function, std::binary_function std::mem_fun , std::bind1st, std::bind2nd