TypeScript Version: 3.6.3

Search Terms:

Union type functions

Code

type A = number[] | string[];
const a = <A>[1];
a.forEach(element => console.log(element)); // error

Expected behavior:

No compile error. (element is inferred to be number | string)

Actual behavior:

Compile error. (Parameter 'element' implicity has 'any' type.)

Playground Link:

http://www.typescriptlang.org/play/?ssl=1&ssc=1&pln=4&pc=1#code/C4TwDgpgBAglC8UB2BXAtgIwgJwNoF0oAfKAZ2GwEskBzAgbgCgBjAeyXKgEMEoAeGAD5cARnxMuAOgBmrbAFEuzABYAKCABsIaCEmAJBUNh1ZbJG1jXVadegJR36UAPTOoObHMZA

Related Issues:

I'm unsure whether or not it is realistic to improve this. Recently I have been working with a number of A[] | B[] types and noticed that most array operations cannot be done on these.