[css-typed-om] What to do when CSSNumericValues form a cycle?

[darrnshn]

With mutable CSSNumericValues, I think it's possible to form cycles:

let a = new CSSMathNegate(0) // a = (- 0)
let b = new CSSMathNegate(a) // b = (- a)
a.value = b // b = (- a) and a = (- b)

If this is possible, should a.value = b throw an error? Otherwise, type checking will get kinda weird and serialization will be impossible.

Follow up question: If we disallow cycles, we can still form a directed acyclic graph. I'm guessing that's allowed, with type checking propagating through the graph when a node changes their value? (i.e. a node has to notify its 'parents' when its type changes)

[tabatkins]

Heh, don't even need to invoke a second object:

let a = new CSSMathNegate(0);
a.value = a; // ?????

I think the fix for this is, upon a.value = b (or equivalent construction), crawl b's value and see if the a object lives anywhere in it.

I think this still allows, say, new CSSMathSum(a, a, a, a, a) to work just fine.

Your follow-up question is more difficult, and means the resolution we made today for CSSUnitValues is kinda useless...

[tabatkins]

Actually, if we solve #494 in the way I want (making .value/.values readonly), this goes away, as you can't construct cycles in the first place.

[darrnshn]

This is pretty much the same as #494. Gonna close this.