[css-typed-om] "Add two types" algorithm seems overly complicated? about css-houdini-drafts HOT 2 CLOSED

The "if" sounds like it checks all the "BaseType -> exponent" values are the same in type1 and type2.

The if checks that the non-zero entries of type1 and type2 are identical; the final type contains all the entries, including zero-valued entries from either input type.

Zero-valued entries are important to maintain because they indicate that the type is still necessary for the input even if it doesn't show up in the output. calc(20deg * (1px / 1em)) has the type {angle: 1, length: 0}, and can't, for example, be represented as a CSSUnitValue (until it's simplified as a computed or used value, at which point it will be just {angle: 1}). A few of the methods care about this, like .to().

But it's perfectly valid to add a calc(20deg * (1px / 1em)) to a calc(30deg); they have compatible types for this purpose (they'll both resolve to angles, eventually). The result will again have the type {angle: 1, length: 0}, preserving the complexity of the inputs.

from css-houdini-drafts.

Ahhhh, thank you very much for the explanation Tab!

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