Definition of Equal?

[Means88]

type A = { a: string; b: string };
type B = { a: string };
type C = { b: string };

// type Equal<X, Y> = <T>() => (T extends X ? 1 : 2) extends <T>() => (T extends Y ? 1 : 2) ? true : false;
/** --- Error --- */
type E0 = Expect<Equal<A, B & C>>; // Type 'false' does not satisfy the constraint 'true'.(2344)
/** ------------- */
type E1 = Expect<A extends B & C ? true : false>;
type E2 = Expect<B & C extends A ? true : false>;

microsoft/TypeScript#27024 (comment)

...which fails because the definition of "identical" doesn't allow an intersection type to be identical to an object type with the same properties.

Is there any negative case T that T extends A different from T extends B & C?

[Means88]

related #9 (comment)

[antfu]

Thanks, I made an update to the utils, adding a new util Alike.

Equal refers to "Strictly equal" while Alike refers to "Strcuturely equal". So in this case Expect<Alike<A, B & C>> would be true while Expect<Equal<A, B & C>> will still fail.