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This content has been automatically translated from Ukrainian.
Idempotent methods are methods or operations in programming that, when executed repeatedly with the same input data, yield the same result as the first execution, without any additional side effects. That is, regardless of how many times the method is executed, its impact on the system remains unchanged.
What does idempotent mean?
The word "idempotent" comes from the Latin words "idem" and "potens".
- "Idem" means "the same".
- "Potens" means "powerful" or "capable".
The term can be interpreted as "capable of maintaining the same" or "that remains unchanged upon repeated application".
The term was first used in mathematics, where it described an operation that, when applied to any element of a set, yields the same result as the original element. Over time, the concept was transferred to other fields, such as programming, where idempotence means that the result of an operation does not change upon repeated execution.
Examples of idempotent methods
Idempotence manifests in many programming and data manipulation contexts. For example, in a file system, the command to create a directory, if it already exists, does not change its state upon repeated execution. Similarly, deleting a file that has already been deleted will have no effect.
In databases, idempotent operations can include UPDATE queries that set a specific value, such as updating a user's status to "active". If the query is executed multiple times with the same value, the state of the database will not change. Similarly, operations like DELETE that delete a record do not result in any changes if the record has already been deleted. More details about REST API can be found at the link.
Caching can also be idempotent. Retrieving a value from the cache, when it has not changed, always returns the same result. Setting a specific value in the cache, when it is already present, does not change the state of the cache.
In the context of RESTful API, the methods PATCH and HEAD are also examples of idempotence. For instance, updating a specific field of an object, if the value is already set, will not change the state of the object. A HEAD request that retrieves the metadata of a resource does not affect its state.
In functional programming, functions such as abs(x) or round(x) are also idempotent. They always return the same value for the same argument, even when called repeatedly.
In configuration management systems like Ansible or Puppet, many operations are idempotent. For example, installing a specific package or creating a configuration file with fixed content will not change the state of the server upon repeated execution of the task.
Even in web interfaces, idempotence is manifested, for instance, in the "Like" button on social networks. If a user has already liked a post and clicks the button again, the state remains unchanged. This example is the simplest and most understandable.
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