Operator overloading

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have different implementations depending on the types of their arguments. Sometimes the overloadings are defined by the language; sometimes the programmer can implement support for new types.

Operator overloading is useful because it allows the developer to program using notation closer to the target domain and allows user types to look like types built into the language. It can easily be emulated using function calls; for an example, consider the integers a, b, c:

a + b * c

In a language that supports operator overloading, and assuming the '*' operator has higher precedence

Precedence

Precedence is a simple ordering, based on either importance or sequence; it may refer to one of the following:* Message precedence of military communications traffic...
 than '+', this is effectively a more concise way of writing:

add (a, multiply (b,c))

However, in C++ templates or even C macro

Macro

A macro in computer science is a rule or pattern that specifies how a certain input sequence should be mapped to an output sequence according to a defined procedure....
s, operator overloading is needed in writing down generic, primitive operations such as summing elements when implementing a vector template. The only way to write primitive addition is a + b and this works for all types of elements only because of its overloading. (Actually, in C++ one could define an overloaded function add to use instead, but not in C.)

A more general variant of operator overloading, called expression reduction, allows expressions containing one or multiple operators to be reduced to a single function call. The expression above could be reduced to:

operator_add_and_multiply_integers(a, b, c)

In this case, the addition operator is overloaded to allow addition on a user-defined type "Date" (in C++):

Date Dateoperator+(Date lhs, Date rhs)

Addition is a binary

Binary operation

In mathematics, a binary operation is a calculation involving two operands, in other words, an operation whose arity is two. Binary operations can be accomplished using either a binary function or binary operator....
 operation, which means it has a left and right operand

Operand

An operand is one of the inputs of an operator in mathematics. The following arithmetic expression shows an example of operators and operands:...
. In C++, the temp object in this case is the left operand and the arguments being passed are the right operands. Note that a unary

Unary operation

In mathematics, a unary operation is an operation with only one operand, i.e. an operation with a single input, or in other words, a function of one variable ....
 operator would receive no arguments since it doesn't have any operands.

Operator overloading has often been criticized because it allows programmers to give operators completely different semantics depending on the types of their operands. For example the use of the << in C++

C++

C++ is a general-purpose programming language. It is regarded as a middle-level language, as it comprises a combination of both high-level programming language and low-level programming language language features....
's: a << 1 shifts the bits in the variable a left by 1 bit if a is of an integer type, but if a is an output stream then the above code will attempt to write a "1" to the stream. Because operator overloading allows the original programmer to change the usual semantics of an operator and to catch any subsequent programmers by surprise, it is usually considered good practice to use operator overloading with care.

Changing the semantics can even happen by accident, as a common pitfall in C++ operator overloading is confusion between the arithmetic operators and assignment

Assignment (computer science)

In computer science the assignment statement sets or re-sets the Value stored in the storage location denoted by a variable name. In most imperative programming computer programming languages the assignment statement is one of the basic Statement s....
 operators: Beginners frequently overload the addition (+) operator but give it the semantics of the assignment by addition (+=) operator, resulting in simple expressions like a + b unexpectedly modifying a.

The common reply to this criticism, given by programmers who favor operator overloading, is that the same argument applies to function overloading as well. Furthermore, even in the absence of overloading, a programmer can define a function to do something totally different from what would be expected from its name. An issue that remains is that languages such as C++ provide a limited set of operator symbols, thus removing from programmers the option of choosing a more suitable operator symbol for their new operation.

Another, more subtle issue with operators is that certain rules from mathematics can be expected or unintentionally assumed. For example the commutativity of + (i.e. that a + b

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