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constAssertions.ts(44,32): error TS2540: Cannot assign to 'x' because it is a read-only property.
constAssertions.ts(61,10): error TS1355: A 'const' assertions can only be applied to references to enum members, or string, number, boolean, array, or object literals.
constAssertions.ts(62,10): error TS1355: A 'const' assertions can only be applied to references to enum members, or string, number, boolean, array, or object literals.
constAssertions.ts(63,10): error TS1355: A 'const' assertions can only be applied to references to enum members, or string, number, boolean, array, or object literals.
constAssertions.ts(118,3): error TS2322: Type '3' is not assignable to type '2'.
==== constAssertions.ts (5 errors) ====
let v1 = 'abc' as const;
let v2 = `abc` as const;
let v3 = 10 as const;
let v4 = -10 as const;
let v5 = +10 as const;
let v6 = 10n as const;
let v7 = -10n as const;
let v8 = true as const;
let v9 = false as const;
let c1 = 'abc' as const;
let c2 = `abc` as const;
let c3 = 10 as const;
let c4 = -10 as const;
let c5 = +10 as const;
let c6 = 10n as const;
let c7 = -10n as const;
let c8 = true as const;
let c9 = false as const;
let vv1 = v1;
let vc1 = c1;
let a1 = [] as const;
let a2 = [1, 2, 3] as const;
let a3 = [10, 'hello', true] as const;
let a4 = [...[1, 2, 3]] as const;
let a5 = [1, 2, 3];
let a6 = [...a5] as const;
let a7 = [...a6];
let a8 = ['abc', ...a7] as const;
let a9 = [...a8];
declare let d: { [x: string]: string };
let o1 = { x: 10, y: 20 } as const;
let o2 = { a: 1, 'b': 2, ['c']: 3, d() {}, ['e' + '']: 4 } as const;
let o3 = { ...o1, ...o2 } as const;
let o4 = { a: 1, b: 2 };
let o5 = { ...o4 } as const;
let o6 = { ...o5 };
let o7 = { ...d } as const;
let o8 = { ...o7 };
let o9 = { x: 10, foo() { this.x = 20 } } as const; // Error
~
!!! error TS2540: Cannot assign to 'x' because it is a read-only property.
let p1 = (10) as const;
let p2 = ((-10)) as const;
let p3 = ([(10)]) as const;
let p4 = [[[[10]]]] as const;
let x1 = { x: 10, y: [20, 30], z: { a: { b: 42 } } } as const;
let q1 = <const> 10;
let q2 = <const> 'abc';
let q3 = <const> true;
let q4 = <const> [1, 2, 3];
let q5 = <const> { x: 10, y: 20 };
declare function id<T>(x: T): T;
let e1 = v1 as const; // Error
~~
!!! error TS1355: A 'const' assertions can only be applied to references to enum members, or string, number, boolean, array, or object literals.
let e2 = (true ? 1 : 0) as const; // Error
~~~~~~~~~~~~~~
!!! error TS1355: A 'const' assertions can only be applied to references to enum members, or string, number, boolean, array, or object literals.
let e3 = id(1) as const; // Error
~~~~~
!!! error TS1355: A 'const' assertions can only be applied to references to enum members, or string, number, boolean, array, or object literals.
let t1 = 'foo' as const;
let t2 = 'bar' as const;
let t3 = `${t1}-${t2}` as const;
let t4 = `${`(${t1})`}-${`(${t2})`}` as const;
function ff1(x: 'foo' | 'bar', y: 1 | 2) {
return `${x}-${y}` as const;
}
function ff2<T extends string, U extends string>(x: T, y: U) {
return `${x}-${y}` as const;
}
const ts1 = ff2('foo', 'bar');
const ts2 = ff2('foo', !!true ? '0' : '1');
const ts3 = ff2(!!true ? 'top' : 'bottom', !!true ? 'left' : 'right');
function ff3(x: 'foo' | 'bar', y: object) {
return `${x}${y}` as const;
}
type Action = "verify" | "write";
type ContentMatch = "match" | "nonMatch";
type Outcome = `${Action}_${ContentMatch}`;
function ff4(verify: boolean, contentMatches: boolean) {
const action : Action = verify ? `verify` : `write`;
const contentMatch: ContentMatch = contentMatches ? `match` : `nonMatch`;
const outcome: Outcome = `${action}_${contentMatch}` as const;
return outcome;
}
function ff5(verify: boolean, contentMatches: boolean) {
const action = verify ? `verify` : `write`;
const contentMatch = contentMatches ? `match` : `nonMatch`;
const outcome = `${action}_${contentMatch}` as const;
return outcome;
}
function accessorNames<S extends string>(propName: S) {
return [`get-${propName}`, `set-${propName}`] as const;
}
const ns1 = accessorNames('foo');
// repro from https://github.com/microsoft/TypeScript/issues/54374
interface Foo54374 {
a: 1;
b: 2;
}
const fooConst54374: Foo54374 = {
a: 1,
b: 3
~
!!! error TS2322: Type '3' is not assignable to type '2'.
!!! related TS6500 constAssertions.ts:113:3: The expected type comes from property 'b' which is declared here on type 'Foo54374'
} as const
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