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Chris Tate
e5ba073468
`JSON.parse(text) as T` for a discriminated union of records took the checked-dynamic route: it parsed the text into a dynamic tree, matched and copied that tree into records, then freed it. The one-pass schema parser now builds these unions directly, as record members, array elements and whole documents. For an object, a shallow scan of its members finds the discriminant's value, which selects the one record arm that holds that literal, and the object is parsed with that arm's schema. An object with a missing, non-string or unknown discriminant, or any member the arm rejects, declines, and the checked route then gives the result or the error as before. The compiler admits unions whose record arms each name their string literals, every literal naming one arm, plus null and undefined arms.