what does (template) rebind<> do?

Question

trying to learn more about how the standard library is actually implemented I\'m inspecting all containers in visual studio.. Here I see some curious structure:

In s

Answer 1

Example in the code of stdc++ : /usr/include/4.8/ext/new_allocator.h

rebind is defined as a structure member of the allocator class; this structure defines a member other that is defined as an instance of the allocator specialized for a different argument type (the other member defines an allocator class that can creates a different type of objects)

 template
    class new_allocator
    {
    public:
      ...
      template
        struct rebind
        { typedef new_allocator<_Tp1> other; };

When it is used:

  typedef typename _Alloc::template rebind<_Tp>::other _Tp_alloc_type;

the type of the allocator is referenced as

  typename _Alloc::template rebind<_Tp>::other 

Now the typedef is used to define _Tp_alloc_type - which can then be used as a shorter name for the same thing.

An example usage is in std::list where the internal list node also needs its allocator, which is redefined from the argument allocator.