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tests/cases/compiler/paramsOnlyHaveLiteralTypesWhenAppropriatelyContextualized.ts(27,23): error TS2345: Argument of type '{ x?: number[] | undefined; y?: string[] | undefined; }' is not assignable to parameter of type '{ y?: number[] | undefined; }'.
Types of property 'y' are incompatible.
Type 'string[] | undefined' is not assignable to type 'number[] | undefined'.
Type 'string[]' is not assignable to type 'number[]'.
Type 'string' is not assignable to type 'number'.
tests/cases/compiler/paramsOnlyHaveLiteralTypesWhenAppropriatelyContextualized.ts(28,23): error TS2345: Argument of type '{ x?: number[] | undefined; y?: string[] | undefined; }' is not assignable to parameter of type '{ x?: string[] | undefined; }'.
Types of property 'x' are incompatible.
Type 'number[] | undefined' is not assignable to type 'string[] | undefined'.
Type 'number[]' is not assignable to type 'string[]'.
Type 'number' is not assignable to type 'string'.
==== tests/cases/compiler/paramsOnlyHaveLiteralTypesWhenAppropriatelyContextualized.ts (2 errors) ====
// Using a homomorphic mapped type over `T`
// Produces a lower-priority inference for `T` than other
// positions, allowing one to override the priority the argument
// order would usually imply
type Lower<T> = { [K in keyof T]: T[K] };
export function appendToOptionalArray<
K extends string | number | symbol,
T
>(
object: { [x in K]?: Lower<T>[] },
key: K,
value: T
) {
const array = object[key];
if (array) {
array.push(value);
} else {
object[key] = [value];
}
}
// e.g.
const foo: {x?: number[]; y?: string[]; } = {};
appendToOptionalArray(foo, 'x', 123); // ok
appendToOptionalArray(foo, 'y', 'bar'); // ok
appendToOptionalArray(foo, 'y', 12); // should fail
~~~
!!! error TS2345: Argument of type '{ x?: number[] | undefined; y?: string[] | undefined; }' is not assignable to parameter of type '{ y?: number[] | undefined; }'.
!!! error TS2345: Types of property 'y' are incompatible.
!!! error TS2345: Type 'string[] | undefined' is not assignable to type 'number[] | undefined'.
!!! error TS2345: Type 'string[]' is not assignable to type 'number[]'.
!!! error TS2345: Type 'string' is not assignable to type 'number'.
appendToOptionalArray(foo, 'x', "no"); // should fail
~~~
!!! error TS2345: Argument of type '{ x?: number[] | undefined; y?: string[] | undefined; }' is not assignable to parameter of type '{ x?: string[] | undefined; }'.
!!! error TS2345: Types of property 'x' are incompatible.
!!! error TS2345: Type 'number[] | undefined' is not assignable to type 'string[] | undefined'.
!!! error TS2345: Type 'number[]' is not assignable to type 'string[]'.
!!! error TS2345: Type 'number' is not assignable to type 'string'.
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