Typescript generics and subtypem

mytest.ts

// Code used to answer bellow stackoverflow question:
// https://stackoverflow.com/a/59363875/8233039

// super class
type _Super<T> = {
    readonly prop1: `bar`
    readonly propT: T
}

const _super: _Super<string> = {
    prop1: `bar`,
    propT: ``
}

// sub class
type _Sub<T> = {
    readonly prop1: `bar`
    readonly propT: T
    readonly prop2: `thux`
}

const _sub:_Sub<number> = {
    prop1: `bar`,
    propT: 10,
    prop2: `thux`,
}

type _DiffSub<T> = {
    readonly prop1: `bar`
    readonly propT: T
    readonly prop3: `different`
}

const _diffSub: _DiffSub<string> = {
    prop1: `bar`,
    propT: ``,
    prop3: `different`,
}

const _subAndDiffSub: _Sub<string> & _DiffSub<string> = {
    prop1: 'bar',
    propT: ``,
    prop2: 'thux',
    prop3: 'different',

}


const func = <A extends _Sub<any> & _DiffSub<any>>(a: A = _subAndDiffSub) => `foo`

// tslint:disable: no-null-keyword

const c0 = func(undefined) // ok
const c1 = func(null) // ok
const c2 = func(() => undefined) // ok
const c3 = func(10) // ok
const c4 = func(`hi`) // ok
const c4_1=func([1,2,3]) // ok
const c5 = func({}) //ok
const c6 = func(_super) // ok
const c7 = func(_sub) //ok
const c8 = func(_diffSub) //ok
const c9 = func(_subAndDiffSub) // ok