language-agnostic - 什么是幂等运算？(What is an idempotent operation?)

Question

什么是幂等运算？

  ask by Will translate from so

Answer 1

In computing, an idempotent operation is one that has no additional effect if it is called more than once with the same input parameters.

(在计算中，幂等运算是指如果使用相同的输入参数多次调用幂等运算，则不会产生任何其他影响。)

For example, removing an item from a set can be considered an idempotent operation on the set.

(例如，从集合中删除项目可以视为对该集合的幂等操作。)

In mathematics, an idempotent operation is one where f(f(x)) = f(x) .

(在数学中，幂等运算是f（f（x））= f（x）的情况 。)

For example, the abs() function is idempotent because abs(abs(x)) = abs(x) for all x .

(例如， abs()函数是幂等的，因为对于所有x abs(abs(x)) = abs(x) 。)

These slightly different definitions can be reconciled by considering that x in the mathematical definition represents the state of an object, and f is an operation that may mutate that object.

(通过考虑数学定义中的x表示对象的状态，并且f是可以使该对象变异的运算，可以调和这些稍有不同的定义。)

For example, consider the Python set and its discard method.

(例如，考虑Python set及其discard方法。)

The discard method removes an element from a set, and does nothing if the element does not exist.

(discard方法从集合中删除一个元素，如果该元素不存在，则不执行任何操作。)

So:

(所以：)

my_set.discard(x)

has exactly the same effect as doing the same operation twice:

(与执行两次相同的操作具有完全相同的效果：)

my_set.discard(x)
my_set.discard(x)

Idempotent operations are often used in the design of network protocols, where a request to perform an operation is guaranteed to happen at least once, but might also happen more than once.

(幂等操作通常用于网络协议的设计中，在该协议中，执行一项操作的请求至少会发生一次，但也可能会发生多次。)

If the operation is idempotent, then there is no harm in performing the operation two or more times.

(如果该操作是幂等的，则两次执行此操作不会有任何危害。)

See the Wikipedia article on idempotence for more information.

(有关更多信息，请参见有关幂等性的Wikipedia文章。)

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^{The above answer previously had some incorrect and misleading examples.}

(^{上面的答案以前有一些不正确和误导性的例子。})

^{Comments below written before April 2014 refer to an older revision.}

(^{以下注释是在2014年4月之前写的，是较旧的版本。})