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node_modules/assert-never/index.ts

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+export function assertNever(value: never, errorMessage?: string): never
+export function assertNever(value: never, getErrorMessage?: (value: unknown) => string): never
+export function assertNever(value: never, noThrow?: boolean): never
+
+/**
+ * Helper function for exhaustive checks of discriminated unions.
+ * https://basarat.gitbooks.io/typescript/docs/types/discriminated-unions.html
+ *
+ * @example
+ *
+ *    type A = {type: 'a'};
+ *    type B = {type: 'b'};
+ *    type Union = A | B;
+ *
+ *    function doSomething(arg: Union) {
+ *      if (arg.type === 'a') {
+ *        return something;
+ *      }
+ *
+ *      if (arg.type === 'b') {
+ *        return somethingElse;
+ *      }
+ *
+ *      // TS will error if there are other types in the union
+ *      // Will throw an Error when called at runtime.
+ *      // Use `assertNever(arg, true)` instead to fail silently.
+ *      return assertNever(arg);
+ *    }
+ */
+export function assertNever(value: never, errorMessageOrNoThrow?: string | ((value: unknown) => string) | boolean): never {
+  if (typeof errorMessageOrNoThrow === 'string') {
+    throw new Error(errorMessageOrNoThrow)
+  }
+
+  if (typeof errorMessageOrNoThrow === 'function') {
+    throw new Error(errorMessageOrNoThrow(value))
+  }
+
+  if (errorMessageOrNoThrow) {
+    return value
+  }
+
+  throw new Error(
+    `Unhandled discriminated union member: ${JSON.stringify(value)}`,
+  );
+}
+
+export default assertNever;