Closure (computer programming) - Wikipedia

Abstraction: Lexical closures — functions bundled with their captured environment

Key points:

• A closure is a record pairing a function with its lexical environment, capturing free variables at creation time so they remain accessible outside their original scope.
• The term was defined by Peter Landin in 1964 (SECD machine); first fully implemented in 1970 in the PAL language; popularized by Sussman and Steele in Scheme (1975).
• Closures require variables to outlive the enclosing scope — this necessitates heap allocation and typically garbage collection; stack-based languages (C, C++) must handle this specially.
• Capture semantics vary: by reference (ECMAScript, C++ [&]) vs. by value (ML, Java final, C++ [=]); lazy languages like Haskell capture computations.
• Common uses include event callbacks, partial application, state encapsulation (analogous to private fields), and implementing control structures (Smalltalk uses closures for all if/while/for).
• Languages differ on how return interacts with closures: ECMAScript return exits the closure only; Smalltalk ^ exits the enclosing method.

Connections: Peter Landin · Scheme · Closures · Functional Programming · Lexical Scoping · First Class Functions

Source: http://en.wikipedia.org/wiki/Closure_%28computer_science%29