Caches and memoize calls

Intro

We've seen defmemo macro that defines a function, creates a cache based on conf, then attaches that cache. It is a combination of a defn to define a function and a memento.core/memo call to create a cache and bind it.

And memo itself is a combination of:

• creating a Cache via memento.core/create (optional, as you can use an existing cache)
• binding the cache to the function via memento.core/bind (a MountPoint is used to connect a function being memoized to the cache)

When memo or equivalent is called with a conf map, a new cache will be created and bound, if a memento.base/Cache instance is given that will be used instead of creating a new cache from a conf map. After memo or bind the function has a MountPoint attached.

Creating a cache

Creating a cache is done by using memento.core/create, which takes a map of configuration (called cache conf). You can use the resulting Cache with multiple functions. The configuration properties (map keys) can be found in memento.config and memento.caffeine.config, look for "Cache setting" in docstring.

If memento.config/enabled? is false, this function always returns memento.base/no-cache, which is a Cache implementation that doesn't do any caching. You can set this at start-up by specifying java property: -Dmemento.enabled=false which globally disables caching.

Binding the cache

Binding the cache to a function is done by memento.core/bind. Parameters are:

• a fn or a var, if var, the root value of var is changed to a memoized version
• a mount point configuration or mount conf for short
• a Cache instance that you want to bind

Mount conf is either a map of mount point configuration properties, or a shorthand (see below). The configuration properties (map keys) can be found in memento.config, look for "function bind" in docstring.

Instead of map of properties, mount conf can be a shorthand, which has the following two shorthands:

• [:some-keyword :another-keyword] -> {:memento.core/tags [:some-keyword :another-keyword]}
• :a-keyword -> {:memento.core/tags [:a-keyword]}

Create + bind combined

You can combine both functions into 1 call using memento.core/memo.

(m/memo fn-or-var mount-conf cache-conf)

To make things shorter, there's a 2-arg variant that allows that you specify both configurations at once:

(m/memo fn-or-var conf)

If conf is a map, then all the properties valid for mount conf are treated as such. The rest is passed to cache create. If conf is a mount conf shorthand then cache conf is considered to be {}. E.g.

(m/memo my-fn :my-tag)

This creates a memoized function tagged with :my-tag bound to a cache that does no caching.