Given two interfaces:

type I1 = {
    a: string
    b: string
    c: number
}

type I2 = {
    a: string
    b: string
    d: string
}

I need to create a type which only has properties which are not shared by the two interfaces.

type Result = XOR<I1, I2>

// should become
type Result = {
    c: number
    d: string
}

I tried this:

type XOR<T1, T2> = {
    [K in keyof (T1 & T2)]: T1[K & keyof T1] | T2[K & keyof T2]
    // ^^ I need something like "not in" here
}

But I am not sure how to only map over keys which are not in both T1 and T2.

I prepared this playground

CodePudding user response：

type XOR<A, B> = {
    [K in Exclude<keyof A | keyof B, keyof A & keyof B>]: K extends keyof A ? A[K] : K extends keyof B ? B[K] : never;
};

Exclude keyof A ∩ keyof B from keyof A ∪ keyof B to get the keys that are only in either A or B. Then just get the right value from A or B for the key.

Playground

Oh, I haven't had my afternoon coffee yet...

type XOR<A, B> = Omit<A & B, keyof A & keyof B>;