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Union doesn't merge objects properties' type #8289
Description
TypeScript Version:
This is reproducible both in VSCode 1.0 and in the playground (https://www.typescriptlang.org/play/#src=...)
Code
interface A {
x: number;
}
interface B {
x: string;
}
const c: A | B = { x: 1 || "a" };
const d: A | B = { x: 1 } || { x: "a" };Expected behavior:
Both c and d should be fine
Actual behavior:
TypeScript reports this error for the const c: A | B = { x: 1 || "a" }; statement:
Type '{ x: number | string; }' is not assignable to type 'A | B'.
Type '{ x: number | string; }' is not assignable to type 'B'.
Types of property 'x' are incompatible.
Type 'number | string' is not assignable to type 'string'.
Type 'number' is not assignable to type 'string'.
Activity
[-]Union doesn't merge object properties' type[/-][+]Union doesn't merge objects properties' type[/+]mhegazy commentedon Apr 25, 2016
{ x: number | string };is neitherAnorB. it becomes easier to see that with more than one property, e.g.RyanCavanaugh commentedon Apr 25, 2016
I should add that we've gotten this request around single-property types a bunch. It turns out to be very difficult to detect all of these cases properly in the compiler.
nicolo-ribaudo commentedon Apr 26, 2016
Mohamed Hegazy (@mhegazy) Thank you, now I see why the current behavior is correct