dft_tools/doc/reference/c++/arrays/containers/swap.rst

swap & deep_swap
==================================

There are two possible interpretation of "swapping two arrays" : 
either use 3 moves like std::swap, i.e. swapping the pointer to the data in memory, 
or making a deep swap, i.e. really swapping all the elements in memeory.

.. _arr_swap:

swap 
--------

* swap just exchange the (shared) pointer to the data in memory, 
  it does not affect the data them self.
  This distinction of importance for views in particular.

* For the regular type, std::swap and swap are equivalent.
  For the views, std::swap is explicitely deleted, since it is incorrect
  due to the lack of move constructor for a view.
  Use `swap` instead.

* **Example** :

.. compileblock::

    #include <triqs/arrays.hpp>
    #include <iostream>
    using triqs::arrays::vector; using triqs::arrays::range; 
    int main () { 
        triqs::arrays::vector<double> V(3), W(4);
        V() = 3; W()=4; // initialize 
        auto VV = V(range (0,2));
        auto VW = W(range (0,2));
      
        std::cout << "V = "<< V << " W = " << W<< " V view "<< VV<< " W view "<< VW<< std::endl;
        swap(V,W);
        std::cout << "V = "<< V << " W = " << W<< " V view "<< VV<< " W view "<< VW<< std::endl;
        swap(VV,VW);
        std::cout << "V = "<< V << " W = " << W<< " V view "<< VV<< " W view "<< VW<< std::endl;
    }

.. _arr_deep_swap:

deep_swap
--------------

.. warning::

   Currently implemented only for triqs::vector and triqs::vector_view.


* deep_swap swaps the data in memory.

* **Example** (compare with swap) :
      
.. compileblock::

    #include <triqs/arrays.hpp>
    #include <iostream>
    using triqs::arrays::vector; using triqs::arrays::range;  
    int main () { 
        triqs::arrays::vector<double> V(3), W(3);
        V() = 3; W()=5; // initialize 
        auto VV = V(range (0,2));
        auto VW = W(range (0,2));
      
        std::cout << "V = "<< V << " W = " << W<< " V view "<< VV<< " W view "<< VW<< std::endl;
        deep_swap(V,W);
        std::cout << "V = "<< V << " W = " << W<< " V view "<< VV<< " W view "<< VW<< std::endl;
        deep_swap(VV,VW);
        std::cout << "V = "<< V << " W = " << W<< " V view "<< VV<< " W view "<< VW<< std::endl;
    }