AI solution for TypeScript puzzle on BFE.dev
42. implement Equal<A, B>

Solution:

type Equal<A, B> =
  (<T>() => T extends A ? true : false) extends
    (<T>() => T extends B ? true : false) ? true : false;

// test cases
type Test1 = Equal<any, any>; // true
type Test2 = Equal<any, 1>; // false
type Test3 = Equal<never, never>; // true
type Test4 = Equal<'BFE', 'BFE'>; // true
type Test5 = Equal<'BFE', string>; // false
type Test6 = Equal<1 | 2, 2 | 1>; // true
type Test7 = Equal<{ a: number }, { a: number }>; // true

Explanation:

We first define the Equal type that takes two types A and B. We use a conditional type with two functions to check if the two types are identical. The first function (<T>() => T extends A ? true : false) checks if any type T extends A. If it does, then it returns true, else it returns false. Similarly, the second function (<T>() => T extends B ? true : false) checks if any type T extends B. If it does, then it returns true, else it returns false. We then use a conditional type to check if the first function extends the second function or vice versa. If it does, then the two types are identical and the Equal type returns true, else it returns false.

Note that the Equal type uses a generic function (<T>() => T extends A ? true : false) instead of a direct comparison between A and B. This is because TypeScript does not allow direct comparisons between two types.

Also note that the Equal type may not work correctly in some cases, such as when dealing with recursive types or types with circular references. However, for the given test cases, it should work as expected.