# binopsbase(3bobcat)

## Binary Operators
(libbobcat-dev_5.07.03)

## 2005-2021

## NAME

BinopsBase - Class template offering class-type binary operators

## SYNOPSIS

#include <bobcat/binopsbase>

## DESCRIPTION

Classes may overload binary operators. A class named Derived may overload binary operators to suit its own needs. It could, e.g., allow two Derived class objects to be added together, or it could define a shift-operation given a size_t right-hand side (rhs) argument.

The available binary operators are *, /, %, +, -, <<, >>, &, |, and ^ (in this man-page they are generically indicated as the `@' operator). In addition, overloaded operator<< and operator>> for stream insertion and extraction are frequently defined.

If a class Derived supports copy and/or move construction and if it offers a swap member (void Derived::swap(Derived &rhs)), and is publicly derived from FBB::BinopsBase<Derived> then once Derived defines a member

        void Class::operator@=(Rhs const &rhs) &&

defining the compound @-operator for anonymous, temporary Derived objects and a Rhs type for its right-hand side operand the following operators are also available:

        Derived &operator@=(Rhs const &rhs) &

        Derived operator@(Derived &&lhs, Rhs const &rhs);
        Derived operator@(Derived const &lhs, Rhs const &rhs);

A similar procedure applies to the insertion and extraction operators. Insertion and extraction operators become available once BinopsBase<Derived> is declared a friend class of Derived. To make the insertion operator available a private member

        void Derived::insert(std::ostream &out) const

must then also be defined, inserting the calling object into out. Analogously, to make the extraction operator available a private member

        void Derived::extract(std::istream &in)

must be defined extrating the calling object from in.

## INHERITS FROM

--

## OVERLOADED OPERATORS

For each defined Derived &&operator@=(Rhs const &rhs) &&, defined in the class Derived the following operators are automatically also available:

        Derived operator@(Derived &&lhs, Rhs const &rhs);
        Derived operator@(Derived const &lhs, Rhs const &rhs);

and

        Derived &operator@=(Rhs const &rhs) &;

The insertion operator becomew available once

        void Derived::insert(std::ostream &out) const

(inserting the calling object into out) has been defined. Analogously, the extraction operator becomes available after defining a private member

        void Derived::extract(std::istream &in)

(extracting the calling object from in).

## FRIEND DECLARATION

To make the insertion and/or extraction operators available the class Derived must also declare

        friend FBB::BinopsBase<Derived>;

## EXAMPLE

    #include <iostream>
    #include <bobcat/binopsbase>

    class Demo1: public FBB::BinopsBase<Demo1>
    {
        friend FBB::BinopsBase<Demo1>;            // for insert/extract

        public:
            void swap(Demo1 &other)
            {}

            Demo1 &&operator+=(Demo1 const &rhs) &&
            {
                std::cout << "adding two Demo1 objects\n";
                return std::move(*this);
            }

    //  Explicit definitions take precedence over functions templates
    //  instantiated from definitions in bobcat/binopsbase.
    //        Demo1 &operator+=(Demo1 const &rhs) &
    //        {
    //            std::cout << "adding (self-defined) two Demo1 objects\n";
    //            return *this;
    //        }

            Demo1 &&operator-=(Demo1 const &rhs) &&
            {
                std::cout << "subtracting two Demo1 objects\n";
                return std::move(*this);
            }

            Demo1 &&operator<<=(Demo1 const &rhs) &&
            {
                std::cout << "shiftleft on two Demo1 objects\n";
                return std::move(*this);
            }

            Demo1 &&operator<<=(size_t rhs) &&
            {
                std::cout << "shiftleft Demo1 object size_t bits\n";
                return std::move(*this);
            }

            void insert(std::ostream &out) const        // requires friend
            {
                out << "inerting a Demo1 object\n";
            }

            void extract(std::istream &in)              // requires friend
            {
                std::cout << "extracting a Demo1 object\n";
            }
    };

    class Demo2: public FBB::BinopsBase<Demo2>
    {
        public:
            void swap(Demo2 &other)
            {}

            Demo2 &&operator+=(Demo2 const &rhs) &&
            {
                std::cout << "adding two Demo2 objects\n";
                return std::move(*this);
            }

            Demo2 &operator+=(Demo2 const &rhs) &
            {
                std::cout << "adding (self-defined) two Demo2 objects";
                return *this;
            }

            Demo2 &&operator^=(Demo2 const &rhs) &&
            {
                std::cout << "xor-ing two Demo2 objects\n";
                return std::move(*this);
            }

            Demo2 &&operator|=(Demo2 const &rhs) &&
            {
                std::cout << "or-ing two Demo2 objects\n";
                return std::move(*this);
            }

    };

    int main()
    {
        Demo1 d1a, d1b;
        Demo1 d1c = d1a + d1b;
        d1a += d1b;
        d1c = Demo1{} + d1b;

        std::cout << "Here we are " << d1c << '\n';
        std::cin >> d1c;

        d1a <<= d1a;
        d1a <<= 5;

        Demo2 d2a, d2b;
        Demo2 d2c = d2a + d2b;
        d2a ^= d2b;
        d2c = Demo2{} ^ d2b;

        d2c = d2c | d2b;
    }

## FILES

bobcat/binopsbase - defines the binary operator function templates

## SEE ALSO

bobcat/binops(3), bobcat(7)

## BUGS

None Reported.

## BOBCAT PROJECT FILES

- https://fbb-git.gitlab.io/bobcat/: gitlab project page;
- bobcat_5.07.03-x.dsc: detached signature;
- bobcat_5.07.03-x.tar.gz: source archive;
- bobcat_5.07.03-x_i386.changes: change log;
- libbobcat1_5.07.03-x_*.deb: debian package containing the libraries;
- libbobcat1-dev_5.07.03-x_*.deb: debian package containing the libraries, headers and manual pages;

## BOBCAT

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

## COPYRIGHT

This is free software, distributed under the terms of the GNU General Public License (GPL).

## AUTHOR

Frank B. Brokken (f.b.brokken@rug.nl).