canonicalize.rs: Dedupe preference-based caching

[glebm]

Extracted from #374.

[NSoiffer]

I'm not seeing the why adding CanonicalizeContextPatternsOptions is an improvement. It actually adds a bit more code to the implementation. I only see one place where there is a minor shortening. The use of a structure maybe adds an extra indirection when running the code. Can you explain why you think this is important? Does it somehow help with your goal of having a stateless MathCAT?

[glebm]

It's not about the amount of code but about eliminating the duplication.

In the stateless PR, there is a new CanonicalizeContext.new_uncached function, which would otherwise also need to manually extract stuff from pref_manager:

impl CanonicalizeContext {
	pub fn new_uncached(pref_manager: &PreferenceManager) -> CanonicalizeContext {
		return CanonicalizeContext {
			patterns: Rc::new( CanonicalizeContextPatterns::new(
				&CanonicalizeContextPatternsOptions::from_prefs(pref_manager)) ),
		};
	}

The options struct also act as the cache key, making the equality comparison a simple ==, which is nice.

The use of a structure maybe adds an extra indirection when running the code

I don't think it does -- it's stored by value in CanonicalizeContextPatternsCache so the number of pointer indirection is the same as before.