Auxiliary data with the cache so that LoaderFunc can be versatile

[kosmas-valianos]

Defining a custom loader is great however its usability is pretty low as you have no access to any user_data that most of the time you need in order to let's say do HTTP(s) requests, file reads etc. This could be solved by being able to add a whatever user_data object when you are creating the ttlcache.Cache object. Exposing this user_data object to the loader along with the key will give the ability to create really powerful loader functions.

[kosmas-valianos]

This auxiliary object should/could be available of course in the other callback functions as well: OnInsertion, OnEviction

[swithek]

Can you provide an example that shows that having this feature in the library would be useful?

Since Loader is an interface, you can already pass the user_data into the implementation yourself:

type CustomLoader[K comparable, V any] struct {
       client *http.Client
}

func (c *CustomLoader[K, V]) Load(c *ttlcache.Cache[K, V], key K) *ttlcache.Item[K, V] {
         // use c.client ...
         // return an item
}

cache := ttlcache.New[string, string](
	ttlcache.WithLoader[string, string](&CustomLoader{
	     // client: ... 
	}),
)

[kosmas-valianos]

Right of course as Loader is an interface. It is even stated in the Readme

a custom or existing implementation of ttlcache.Loader can be used

👌