'IsEqual util type in Typescript doesn't work as expected [duplicate]

I write a IsEqual generic type like that :

type IsEqual<T, U> = T extends U 
  ? U extends T 
    ? true
    : false
  : false

type Test1 = IsEqual<number, 3>  // false, ok

type Test2 = IsEqual<true, false> // false, ok

type Test3 = IsEqual<boolean, true> // boolean -> ? 

type Test4 = IsEqual<true, boolean> // boolean -> ?

What happens here ?

And how to reliably check if a type is the exact same as another ? (not a subtype)

typescript

Solution 1:^[1]

You need to wrap T and U in brackets in the body of the typedef, i.e:

type IsEqual<T, U> = [T] extends [U] 
  ? [U] extends [T]
    ? true
    : false
  : false

Otherwise, TypeScript will distribute the types and evaluate IsEqual<boolean, true> as IsEqual<true, true> | IsEqual<false, true>. Source: this github comment.

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution	Source
Solution 1	Bbrk24

'IsEqual util type in Typescript doesn't work as expected [duplicate]

Solution 1:[1]

Sources

Related Questions

Solution 1:^[1]