How to extract interface from class, exact match

[zerkalica]

How to extract properties interface from class and do exact match?

class A {
 a: string
}

const likeA: $ShapeWithExactMatch<A> = {} // need a: string

I try $Shape, but it do not exact match.

EDIT: Full example

export default class A {
    some: string

    constructor<K: {[_: $Keys<A>]: string}>(rec?: K, old?: K) {
        Object.assign(this, this.constructor.defaults, rec, old)
    }

    copy(rec: {[_: $Keys<A>]: string}): this {
        return new this.constructor(rec, this)
    }

    static defaults = {
         some: 'default'
    }
}

const a = new A({some: 'test'})
const b = a.copy({info: 'qq'})