Operator overloading is a programming technique in which some or all of operators like +, = or == can be treated as functions and can be defined or redefined for new types. Sometimes defining new operators is allowed. This is usually only a syntactic sugar, and it can be easily emulated by function calls:
|with operator overloading:||a + b * c|
|without operator overloading:||our_new_type_add (a, our_new_type_multiply (b,c))|
Only in case when operators can be called implicitely they are of some use other than esthetics. This is the case with Ruby operator to_s, which returns a string representation of an object and with operators in PostgreSQL, where mathematical transformations can be defined on operators and PostgreSQL may use many optimalizations to expressions that use them.
Operator overloading has been criticised because it allows programmers to give operators completely different functionality depending on the types of their operands. C++'s usage of the "<<" operator is a particularly bad example: The expression
a << 1
will return two times the value of a if a is an integer variable, but if a is an output stream instead this will write "1" into it.
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