00645 - Medium diff (https://github.com/type-challenges/type-challenges/blob/main/questions/00645-medium-diff/README.md)

Diff.ts

type Diff<
  Obj1, 
  Obj2, 
  SameKeys extends keyof Obj1 = keyof Obj1 & keyof Obj2
> = Omit<{
  [K in (keyof Obj1 | keyof Obj2)]: 
    K extends keyof Obj1 
      ? Obj1[K] 
      : K extends keyof Obj2 
        ? Obj2[K] 
        : never
}, SameKeys>

type Foo = {
  name: string
  age: string
}
type Bar = {
  name: string
  age: string
  gender: number
}
type Coo = {
  name: string
  gender: number
}

type Diff1 = Diff<Foo, Bar> // { gender: number }
type Diff2 = Diff<Bar, Foo> // { gender: number }
type Diff3 = Diff<Foo, Coo> // { age: string; gender: number }
type Diff4 = Diff<Coo, Foo> // { age: string; gender: number }