2016-09-25 00:58:53 +02:00
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// Widening vs. non-widening literal types
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function f1() {
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const c1 = "hello"; // Widening type "hello"
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let v1 = c1; // Type string
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const c2 = c1; // Widening type "hello"
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let v2 = c2; // Type string
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const c3: "hello" = "hello"; // Type "hello"
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let v3 = c3; // Type "hello"
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const c4: "hello" = c1; // Type "hello"
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let v4 = c4; // Type "hello"
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}
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function f2(cond: boolean) {
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const c1 = cond ? "foo" : "bar"; // widening "foo" | widening "bar"
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const c2: "foo" | "bar" = c1; // "foo" | "bar"
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const c3 = cond ? c1 : c2; // "foo" | "bar"
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const c4 = cond ? c3 : "baz"; // "foo" | "bar" | widening "baz"
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const c5: "foo" | "bar" | "baz" = c4; // "foo" | "bar" | "baz"
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let v1 = c1; // string
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let v2 = c2; // "foo" | "bar"
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let v3 = c3; // "foo" | "bar"
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let v4 = c4; // string
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let v5 = c5; // "foo" | "bar" | "baz"
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}
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function f3() {
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const c1 = 123; // Widening type 123
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let v1 = c1; // Type number
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const c2 = c1; // Widening type 123
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let v2 = c2; // Type number
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const c3: 123 = 123; // Type 123
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let v3 = c3; // Type 123
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const c4: 123 = c1; // Type 123
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let v4 = c4; // Type 123
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}
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function f4(cond: boolean) {
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const c1 = cond ? 123 : 456; // widening 123 | widening 456
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const c2: 123 | 456 = c1; // 123 | 456
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const c3 = cond ? c1 : c2; // 123 | 456
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const c4 = cond ? c3 : 789; // 123 | 456 | widening 789
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const c5: 123 | 456 | 789 = c4; // 123 | 456 | 789
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let v1 = c1; // number
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let v2 = c2; // 123 | 456
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let v3 = c3; // 123 | 456
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let v4 = c4; // number
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let v5 = c5; // 123 | 456 | 789
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}
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function f5() {
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const c1 = "foo";
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let v1 = c1;
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const c2: "foo" = "foo";
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let v2 = c2;
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const c3 = "foo" as "foo";
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let v3 = c3;
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const c4 = <"foo">"foo";
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let v4 = c4;
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}
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2018-05-22 01:43:55 +02:00
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declare function widening<T>(x: T): T;
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declare function nonWidening<T extends string | number | symbol>(x: T): T;
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function f6(cond: boolean) {
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let x1 = widening('a');
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let x2 = widening(10);
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let x3 = widening(cond ? 'a' : 10);
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let y1 = nonWidening('a');
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let y2 = nonWidening(10);
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let y3 = nonWidening(cond ? 'a' : 10);
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}
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2016-09-25 00:58:53 +02:00
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// Repro from #10898
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type FAILURE = "FAILURE";
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const FAILURE = "FAILURE";
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type Result<T> = T | FAILURE;
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function doWork<T>(): Result<T> {
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return FAILURE;
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}
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function isSuccess<T>(result: Result<T>): result is T {
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return !isFailure(result);
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}
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function isFailure<T>(result: Result<T>): result is FAILURE {
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return result === FAILURE;
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}
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function increment(x: number): number {
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return x + 1;
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}
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let result = doWork<number>();
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if (isSuccess(result)) {
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increment(result);
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}
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// Repro from #10898
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type TestEvent = "onmouseover" | "onmouseout";
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function onMouseOver(): TestEvent { return "onmouseover"; }
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2018-05-22 01:43:55 +02:00
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let x = onMouseOver();
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// Repro from #23649
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export function Set<K extends string>(...keys: K[]): Record<K, true | undefined> {
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const result = {} as Record<K, true | undefined>
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keys.forEach(key => result[key] = true)
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return result
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}
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export function keys<K extends string, V>(obj: Record<K, V>): K[] {
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return Object.keys(obj) as K[]
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}
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type Obj = { code: LangCode }
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const langCodeSet = Set('fr', 'en', 'es', 'it', 'nl')
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export type LangCode = keyof typeof langCodeSet
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export const langCodes = keys(langCodeSet)
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const arr: Obj[] = langCodes.map(code => ({ code }))
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2018-12-18 20:58:06 +01:00
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// Repro from #29081
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function test<T extends { a: string, b: string }>(obj: T): T {
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let { a, ...rest } = obj;
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return { a: 'hello', ...rest } as T;
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}
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2019-07-05 04:27:03 +02:00
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// Repro from #32169
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declare function f<T>(x: T): NonNullable<T>;
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enum E { A, B }
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const a = f(E.A);
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const b: E.A = a;
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