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This commit adds a new function `assertNever` to the `assert` submodule. This function is particularly useful when we want to check whether we properly handle all the variants of a discriminated union. Ref: https://www.typescriptlang.org/docs/handbook/unions-and-intersections.html#union-exhaustiveness-checking --------- Co-authored-by: Yoshiya Hinosawa <stibium121@gmail.com>
37 lines
677 B
TypeScript
37 lines
677 B
TypeScript
// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
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import { AssertionError, assertNever, assertThrows } from "./mod.ts";
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Deno.test("assertNever: exhaustiveness check", () => {
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type Kinds = "A" | "B";
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function doA() {
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// ...
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}
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function doB() {
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// ...
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}
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function handleKind(kind: Kinds) {
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switch (kind) {
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case "A":
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doA();
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break;
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case "B":
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doB();
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break;
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default:
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assertNever(kind);
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}
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}
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handleKind("A");
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handleKind("B");
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});
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Deno.test("assertNever throws AssertionError", () => {
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assertThrows(() => {
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assertNever(42 as never);
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}, AssertionError);
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});
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