Closed
Description
I have a variable of a union type (A or B). I have a function with overloads for A and for B.
It seems definitely sensible to allow passing this variable to the function. But TS fails on compilation.
interface A { foo: string };
interface B { bar: string };
let value: A | B;
function test(obj: A): boolean;
function test(obj: B): boolean;
function test(obj) { return true; }
test(value);See Playground
Expected behavior:
No compile errors.
Actual behavior:
lib.ts(28,6): error TS2345: Argument of type 'A | B' is not assignable to parameter of type 'B'.
Type 'A' is not assignable to type 'B'.
Property 'bar' is missing in type 'A'.
I didn't test on all versions but I guess it doesn't depend on particular version as it's failing in the Playground.
I understand that instead of using overloads I can create a function with union type for argument:
function test(obj: A | B): boolean;
but in my case it's not acceptable. Actually the provided code is a simplified example of bigger problem.
I have a component with an option which type is string[] | Map<string> where Map is
export interface Map<T> {
[key: string]: T;
}
I need to pass this option to a function from Undescore like these ones:
contains<T>(list: _.List<T>, value: T): boolean;
contains<T>(object: _.Dictionary<T>, value: T): boolean;