idempotent
1. A function f : D -> D is idempotent if
f (f x) = f x for all x in D.
I.e. repeated applications have the same effect as one. This can be
extended to functions of more than one argument,
e.g. Boolean & has x & x = x. Any value in the image
of an idempotent function is a fixed point of the
function.
2. This term can be used to describe C header files, which contain common
definitions and declarations to be included by several source files. If a header
file is ever included twice during the same compilation (perhaps due to nested
#include files), compilation errors can result unless the header file has
protected itself against multiple inclusion; a header file so protected is said
to be idempotent.
3. The term can also be used to describe an initialisation subroutine that is
arranged to perform some critical action exactly once, even if the routine is
called several times.
[Jargon File]
(1995-01-11)
Nearby terms:
Idealized CSP « Idealized Instruction Set « IDEF «
idempotent » identifier » {IDF} » I didn't
change anything!
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