Configure caching on a per-key basis

[kalekundert]

For example, I might want to recalculate an attribute each time if its value involves a Method key, since that could depend on other attributes of the object, but cache the attribute if it involves any other key. Note that this depends on which values are actually used; e.g. consumed by the pick() generator. Key should take its default caching behavior from the configs it matches, so that static configs can be cached by default while potentially dynamic configs can be looked up every time.

The API would be straight-forward:

x = appcli.param(
        Key(MyConfig, 'x', dynamic=False),
)

[kalekundert]

On the topic of caching, I'm also wondering if would be possible to implement @cached_property-style caching, e.g. where the cached value is written to the instance dictionary such that it shadows the descriptor and can be read/written with no performance penalty.

Some thoughts on how to do this:

• I'd still need to clear the cache on load(). To do this, I'd need to maintain a list of the attributes that have been cached.
• It might be worth having some values that don't get recalculated even on a load. This could be used to prevent very expensive values from accidentally getting recalculated. Not sure if this is a good idea, but I could implement it by having the "list of cached attributes" be a "attribute to cache type" dictionary.
• I think this would simplify the code, because I wouldn't need any code to check if a value is cached. The code would never get to me if there were. So I could just unconditionally calculate a new value, then check the dynamic setting to decide whether or not to set the cache.

I can't completely get rid or the get and set arguments, though. SWMB uses get a lot, in particular for binding arguments. set is less used, but goes hand-in-hand with get.

[kalekundert]

Pseudo-code implementation:

• Getter gains a dynamic attribute.
  • Key.dynamic: taken from config
  • Method.dynamic: True by default
  • Func.dynamic: False by default
  • Value.dynamic: False
• ValuesIter gains dynamic attribute that is set by the iterator itself during iteration. Basically, it will be False unless any getter with dynamic == True is encountered.
• param stores ValuesIter.dynamic in its state, and uses it to decide when to refresh the cache.