In computer programming, operator overloading (less commonly known as ad-hoc polymorphism) is a specific case of polymorphism in which some or all of operators like +, = or == are treated as polymorphic functions and as such have different behaviours depending on the types of its arguments. Operators need not always be symbols.
Operator overloading 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 implicitly they are of some use other than aesthetics. 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.
Criticism
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.
Catalog
Languages that support operator overloading and declaring new operators: PostgreSQL version of SQL, Ruby, Haskell
Languages that support operator overloading: Ada, C++, C#, D, Python, Ruby
Languages that don't support operator overloading: C, Pascal, Delphi, Java, Visual Basic, Perl
