What is the difference between "Set" and "Add" for ObjectCache?

Question

From the doc

Add(CacheItem, CacheItemPolicy) : When overridden in a derived class, tries to insert a cache entry into the cache as a CacheItem instance, and adds details about how the entry should be evicted. [1]

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Set(CacheItem, CacheItemPolicy) : When overridden in a derived class, inserts the cache entry into the cache as a CacheItem instance, specifying information about how the entry will be evicted. [2]

I see little difference in the wording (tries to) and signature (set is a sub, add returns a boolean), but I'm not sure which one I should use and if there is really something different between both.

Answer 1

The Main difference is that the Add() method tries to insert a cache without overwriting an existing cache entry with the same key.

While the Set() method will overwrite an existing cache entry having the same key. [ However If the key for an item does not exist, insertion will be done as a new cache entry ].

Above was the difference in terms of their functionality.

Syntactical Difference:

One significant syntactical difference is that the Add() method returns a Boolean which is true if insertion succeeded, or false if there is already an entry in the cache that has the same key as item. The Set() method has a void return type.

One last point that internal implementation of Add() method actually calls its corresponding version of AddOrGetExisting() method.

 public virtual bool Add(CacheItem item, CacheItemPolicy policy) {     return this.AddOrGetExisting(item, policy) == null; }