Provided by: libbobcat-dev_3.19.01-1ubuntu1_amd64 bug


       FBB::fswap - generic template fast swap function


       #include <bobcat/fswap>


       The  information stored in objects frequently needs to be swapped. A well-known example is
       the swapping operation required when implementing an overloaded assignment  operator.  For
       example, the generic form of the operator assignment operator is:

           Class &operator=(Class const &other)
               Class tmp(other);
               return *this;

       The swap functionality merely swaps the contents of the current object and another object.
       The standard std::swap function calls the class’s  operator=  function  to  swap  objects.
       Newer  implementations  might  use  move-operations  to  increase the speed of the swaping
       operation, but in both cases some form of  the  assignment  operator  must  be  available.
       Swapping,  however, might be possible when assignemnt isn’t. Classes having reference data
       members usually don’t offer assignment operators but  swapping  might  be  a  well-defined

       It  is  well known that objects can be installed in a block of memory using placement new,
       using a block of memory the size of the object to construct the object  it.  This  is  the
       foundation of the template function FBB::fswap (fast swap). This swap function merely uses
       the memory occupied by objects to implement the swapping operation and it may therefore be
       used  with classes having const data members, reference data members, ponters to allocated
       memory etc, etc. The function simply uses a spare block of memory the size of  the  object
       to  be  swapped.  It  then  uses  memcpy(3)  to  swap the information contained in the two
       objects, using the spare block of memory as a placeholder.

       The function uses partial specializations to optimize the swapping operation  for  objects
       of sizes 1, 2, 4 or 8 bytes. It uses memcpy(3) for objects of other sizes.


       All  constructors,  members,  operators  and manipulators, mentioned in this man-page, are
       defined in the namespace FBB.




       o      fswap(Type &lhs, Type &rhs):
              This template function swaps the contents of the two objects. It can be  used  with
              classes  having  const data members, reference members, pointer members or standard
              value-typed data members.


       #include <iostream>
       #include "../fswap"

       class Demo
           std::ostream &d_out;
           size_t d_value;

               Demo(std::ostream &out = std::cerr, size_t value = 0)

               void show(char const *msg)
                   d_out << msg << ". Value: " << d_value << ’\n’;

       using namespace std;

       int main()
           Demo d1;
           Demo d2(cout, 12);

           FBB::fswap(d1, d2);

 "This is d1");              // to cerr: 12
 "This is d2");              // to cout: 0


       bobcat/fswap - defines the class interface


       bobcat(7), memcpy(3)


       The fswap function should not be applied mechanically to swap objects  of  classes  having
       pointer data members defining, e.g., a linked list. Consider a list of four objects like:

           A -> B -> C -> D

       fast-swapping B and C would result in the following corrupted list:

                      |      |
           A -> C -+  +-> B -+   +-> D
                   |             |

       However, classes implementing a data structure like a linked-list might still benefit from
       fast swapping operations: by implementing their own swap member they could first use  fast
       swapping  to  swap  the  objects,  followed  by  another  fast swap to unswap their `next’

       The fswap function should also not be used for objects defining (back-)pointers  to  their
       own data. Consider the following objects using pointers to data and (back-)pointers to the
       original objects:

           Before fswapping:
               A                                  B
              +--------+   +-----------+         +--------+   +-----------+
              |        |   |           |         |        |   |           |
            +--> *Aimp------> *A (back)--+     +--> *Bimp------> *B (back)--+
            | |        |   |           | |     | |        |   |           | |
            +--**Aimp  |   +-----------+ |     +--**Bimp  |   +-----------+ |
              +--------+ <---------------+       +--------+ <---------------+

           After fswapping:
           +-------------|--|-----------------+             | |
           |   A         |  v                 |   B         | v
           |  +--------+ | +-----------+      |  +--------+ | +-----------+
           |  |        | | |           |      |  |        | | |           |
         +-----> *Bimp---+ |  *A (back)--+    +---> *Aimp---+ |  *B (back)--+
         | |  |        |   |           | |       |        |   |           | |
         | +---**Bimp  |   +-----------+ |    +---**Aimp  |   +-----------+ |
         |    +--------+ <---------------+    |  +--------+ <---------------+

       After the swap **Bimp should point to Bimp’s address (now at A), but in fact it points  to
       Aimp’s  address  (now  at  B).  Likewise,  the back pointers still point at their original
       objects rather than at their swapped objects.

       All stream classes define such pointers and can therefore not be swapped using fswap.

       The bottom line being that fswap should only be used for self-defined classes for which it
       can be proven that fast-swapping does not corrupt the values of its pointer data.


       o      bobcat_3.19.01-x.dsc: detached signature;

       o      bobcat_3.19.01-x.tar.gz: source archive;

       o      bobcat_3.19.01-x_i386.changes: change log;

       o      libbobcat1_3.19.01-x_*.deb: debian package holding the libraries;

       o      libbobcat1-dev_3.19.01-x_*.deb:  debian  package holding the libraries, headers and
              manual pages;

       o public archive location;


       Bobcat is an acronym of `Brokken’s Own Base Classes And Templates’.


       This is free software, distributed under the terms  of  the  GNU  General  Public  License


       Frank B. Brokken (