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Chris Tate
970a53c1ba
A number[], string[] or boolean[] seen as (T | undefined)[] through a cast, a binding or a parameter is the same array in Node: undefined written through either name is visible through both. The type mapper now stores (T | undefined)[] of a number, string or boolean T as T elements, which hold a present undefined by their slot state, so the wider name shares the storage instead of converting to a separate union array. Writers of these arrays store undefined as a present undefined: element writes, push, unshift and splice, literals, Array.from (with a length or a mapper), Array.of, generator drains, flatMap, rest packs, copies from Map and Set values and Object.values, and checked conversions from dynamic values. Promise.all over Promise<T | undefined>[] fills the result inside the combinator's settlement, so it settles on Node's turn. The element-state analysis counts callbacks and iterables whose checker type admits undefined. Readers keep their optional reads: index reads through a union of arrays, searches with a direct needle, and asserted reads, which throw a TypeError for undefined. Comparators and callbacks that receive present elements take the element type, without an adapter.