Type Alias StrictExtract<T, U>

StrictExtract: Extract<T, U>

A stricter version of Extract that enforces valid extraction shapes.

StrictExtract tries to prevent accidentally extracting values that could never exist in T.

Type Parameters

T
The source union type
U extends ExcludeExtractConstraint<T>
The extraction type (must conform to T)

Example: Basic usage (same as `Extract`)

type Result = StrictExtract<"a" | "b" | "c", "a">;
//   ^?
// "a"

Example: Extracting a union member by shape

type Input =
  | { type: "a"; value: string }
  | { type: "b"; value: number };

type Result = StrictExtract<Input, { type: "a" }>;
//   ^?
// { type: "a"; value: string }

Example: Invalid extraction is rejected

type Input =
  | { a: string }
  | { b: number };

type Invalid = StrictExtract<
  Input,
  //@ts-expect-error - not compatible with any member of Input
  { c: boolean }
>;