add a supertype constraint

[zpdDG4gta8XKpMCd]

currently when we see a constraint <A extends B> it means A is a subtype of B, so that

declare var a: A;
declare var b: B;
b = a; // allowed
a = b; // not allowed

consider adding a new constraint of the reversed relation: <A within B> that would mean A is a supertype of B (or in other words B is subtype of A), so that:

declare var a: A;
declare var b: B;
b = a; // not allowed
a = b; // allowed

use case

i have a BigFatClass with 50 methods and a 1 little property, now i want to run some assertions over it, if i declare these assertions like expect<T>() and toEqual<T> of the same T then toEqual asks me for 50 methods that don't matter for the test, and that's the problem

what i need it to declare expect<T>() and toEqual<U within T>() so that i could simply write:

expect(new BigFatClass()).toEqual({ value: true });

[aaronbeall]

Can't you use Partial<T> for your assertion?

[zpdDG4gta8XKpMCd]

@aaronbeall yes, it should work for this very use case, thanks for an idea

[RyanCavanaugh]

Most recent one tracking this is #14520

[zpdDG4gta8XKpMCd]

thanks