typable

typable is a mini library to include dynamic casting in TypeScript.

Class TypeRep<T>

new TypeRep<T>(uniqueName:string, …inheritance: TypeRep<any>[])

Creates a TypeRep for type T.

TypeRep<T>::is<R>(other: TypeRep<R>): this is TypeRep<T&R>

Detects whether this typeRep is a sub-type-rep of other.

TypeRep<T>::equal<R>(other: TypeRep<R>):this is TypeRep<T&R>

Detects whether this typeRep is equivalent to other.

Identical to typeRep.is(other) && other.is(typeRep).

Interface Typable<T = {}>

Typable<T>::dynamicCast<U>(tr: TypeRep<U>): undefined | U

This method is required for all Typables to implement: given a TypeRep<U>, the object should return an instance of U, if T is a subtype of U, or undefined for other cases. TypeRep<T>::is could be used in implementation.

Function implDynamicCast<U, T>(tr: TypeRep<U>, obj: Typable<T>, trObj: TypeRep<T>): undefined | U

This function is an utility function used to simplify implementation of dynamicCast. Typical use is:

const TypeRepOfC = new TypeRep<C>(......);
class CImpl implements Typable<C> {
    public a = 1;
    public b = 2;
    public c = 3;
 
    dynamicCast<U>(tr: TypeRep<U>): undefined | U {
        return implDynamicCast(tr, this, TypeRepOfC);
    }
}

Sample

import { implDynamicCast, Typable, TypeRep } from "typable";
 
const A = new TypeRep<A>("A");
interface A {
    readonly a: number;
}
const B = new TypeRep<B>("B", A);
interface B extends A {
    readonly b: number;
}
const C = new TypeRep<C>("C", A);
interface C extends A {
    readonly c: number;
}
const D = new TypeRep<D>("D", B, C);
interface D extends B, C {
    readonly d: number;
}
 
class CImpl implements Typable<C> {
    public a = 1;
    public b = 2;
    public c = 3;
 
    dynamicCast<U>(tr: TypeRep<U>): undefined | U {
        return implDynamicCast(tr, this, C);
    }
}
class BCImpl implements Typable<B>, Typable<C> {
    public a = 1;
    public b = 2;
    public c = 3;
 
    dynamicCast<U>(tr: TypeRep<U>): undefined | U {
        return implDynamicCast(tr, this, B) || implDynamicCast(tr, this, C);
    }
}
class DImpl implements Typable<D> {
    public a = 1;
    public b = 2;
    public c = 3;
    public d = 4;
 
    dynamicCast<U>(tr: TypeRep<U>): undefined | U {
        return implDynamicCast(tr, this, D);
    }
}