subtraction-type.ts

// see also https://www.npmjs.com/package/subtractiontype.ts

    
// for literal unions
type Sub0<
    O extends string,
    D extends string,
> = {[K in O]: (Record<D, never> & Record<string, K>)[K]}

type Sub<
    O extends string,
    D extends string,
    // issue 16018
    Foo extends Sub0<O, D> = Sub0<O, D>
> = Foo[O]

type Dissoc<
    O,
    D extends string,
    // issue 16018
    Foo extends Sub0<keyof O, D> = Sub0<keyof O, D>
> = Pick<O, Foo[keyof O]>
    
// example
type Input = { X: 1, Y: 2, Z: 3 }
type Expected = { Y: 2, Z: 3 }
type Output = Dissoc<'X', Input>
type Check<
    To extends Output = Expected,
    From extends Expected = Output
> = never

    
// for literal unions
// example
type Output2 = Sub<'X', 'Y' | 'X'>