In computer science, a type class is a type system construct that supports ad-hoc polymorphism. This is achieved by adding constraints to type variables in parametrically polymorphic types. Such a constraint typically involves a type class T and a type variable a, and means that a can only be instantiated to a type whose members support the overloaded operations associated with T.
Type classes first appeared in the Haskell programming language, and were originally conceived as a way of implementing overloaded arithmetic and equality operators in a principled fashion. In contrast with the "eqtypes" of Standard ML, overloading the equality operator through the use of type classes in Haskell does not require extensive modification of the compiler frontend or the underlying type system.
Since their creation, many other applications of type classes have been discovered.
Read more about Type Class: Overview, Higher-kinded Polymorphism, Multi-parameter Type Classes, Functional Dependencies, Other Approaches To Operator Overloading, Related Notions
Famous quotes containing the words type and/or class:
“Are God and Nature then at strife,
That Nature lends such evil dreams?
So careful of the type she seems,
So careless of the single life;”
—Alfred Tennyson (1809–1892)
“... social evils are dangerously contagious. The fixed policy of persecution and injustice against a class of women who are weak and defenseless will be necessarily hurtful to the cause of all women.”
—Fannie Barrier Williams (1855–1944)