What's the difference between add, set, and replace in Memcache

People who have used memcache have a doubt, that is why there is a memcache in the Add method, a set method, a replace, these methods have what kind of difference, below we analyze the differences between these methods:

Memcache::add method: The Add method is used to add a data to the Memcache server to be cached.

Memcache::set method: The Set method is used to set the cached content of a specified key, and the Set method is the collection of the Add method and the Replace method

Mmecache::replace method: The Replace method replaces the cached content of a specified key and returns False if key does not exist

Comparison:

Method	When key exists	When key does not exist
Add	False	True
Replace	Replace (true)	False
Set	Replace (true)	True

I believe you know how to use these methods in the future, it is so simple

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