Make type unions work with generics

[mertdeg2]

TypeScript Version: all

Code

type foo = string|number;

class Baz<T extends foo> {
  x: T = 'a';
}

Expected behavior:
I expected to be able to assign something to x. (As my coworkers explained to me) In this case, you can't assign anything to x, because "T extends foo" means T is subtype of foo (Not the other way around).

Second Expected behavior:
Given above, I think it would be nice if TS allowed something like:

type foo = string|number;

class Baz<foo extends T> {
  x: T = 'a';
}

Or maybe something like below (which i heard is supported in Java)?

type foo = string|number;

class Baz<foo super T> {
  x: T = 'a';
}

[mhegazy]

The first example is wrong as you already noted. Baz<number> is a valid instantiation, and thus x: number = "a" is invalid.
The second is tracked by #14520

[mertdeg2]

Thanks @mhegazy

[typescript-bot]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.