Utilizing mapped types in a proxy solution

As I was going through the TS Handbook, I stumbled upon mapped types where there's a code snippet demonstrating how to wrap an object property into a proxy.

type Proxy<T> = {
    get(): T;
    set(value: T): void;
}
type Proxify<T> = {
    [P in keyof T]: Proxy<T[P]>;
}
function proxify<T>(o: T): Proxify<T> {
   // ... wrap proxies ...
}
let proxyProps = proxify(props);

While trying to enhance the proxify function with my own implementation, I encountered the following issue:

function proxify<T>(t: T): Proxify<T> {
    let result = <Proxify<T>>{};
    for (const k in t) {
      result[k] = {    //(*) from that moment I lose strong typing  
        get: () => t[k],
        set: (value) => t[k] = value
      }
    }
    return result;
  }

The problem arises within the loop as I'm unable to enforce type control and everything defaults to any. How can I address this issue while ensuring the correctness of my implementation?

Answer №1

The approach appears to be solid. Although there is a slight compromise on safety when creating the object, it's not completely lost. You may find yourself pleasantly surprised by the amount of code reduction achieved.

function proxyfy<T>(t: T): Proxyfy<T> {
    let result = <Proxyfy<T>>{};
    for (const k in t) { // k is of type Extract<keyof T, string> ensuring validity as a key of T
        result[k] = { 
            get: () => t[k],
            set: (value) => t[k] = value
        }
    }
    return result;
}

Answer №2

My approach to implementation is outlined below. Despite my efforts, I was unable to find a way to enforce type safety in the get and set methods. It would have been more graceful if there existed a method to define properties such as get():PropType , set(value:PropType)

function createProxy<T>(obj: T): ProxyObject<T> {
        const proxy: ProxyObject<T> = <ProxyObject<T>>{};
        Object.keys(obj).map((key) => {
            proxy[key] = {
                get() {
                    return obj[key];
                },
                set(value) {
                    obj[key] = value;
                }
            };

        });
        return proxy;
    }

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