How can Lazy<T> be integrated into TypeScript?

Question

How can Lazy<T> be integrated into TypeScript?

While working in .NET, I came across the Lazy<T> type which proved to be very helpful for tasks like lazy loading and caching. However, when it comes to TypeScript, I couldn't find an equivalent solution so I decided to create my own.

export interface Factory<TResult> { () : TResult; }

export class Lazy<T> {
    factoryOutput : T;
    isValueSet : boolean;

    constructor(private factory : Factory<T>) { }    

    get value() {
        if (!this.isValueSet) {
            this.factoryOutput = this.factory();
            this.isValueSet = true;
        }
        return this.factoryOutput;
    }
}

Having to develop my own solution has raised some questions:

Is there an existing alternative that I may have overlooked in TypeScript?
Could there be any flaws in my approach to wanting a .NET-style Lazy<T> in TypeScript?

typescript

Answer 1

Answer №1

A class is not necessary in this scenario. By utilizing a function with a closure, you can achieve the desired functionality.

function createLazyValue<T>(factory: () => NonNullable<T>) {
    let value: T | undefined;
    return () => value ?? (value = factory());
}

To use it, simply follow this format:

var lazyGreeting = createLazyValue(() => {
    console.debug("Factory function for greeting called");
    return "Greetings";
});

var lazyFarewell = createLazyValue(() => {
    console.debug("Factory function for farewell called");
    return "Farewell";
});

for(var count = 0; count < 4; count++) {
    console.debug(lazyGreeting());
    console.debug(lazyFarewell());
}

The factory function will only execute once, ensuring efficient performance.

Answer 2

A class is not necessary in this scenario. By utilizing a function with a closure, you can achieve the desired functionality.

function createLazyValue<T>(factory: () => NonNullable<T>) {
    let value: T | undefined;
    return () => value ?? (value = factory());
}

To use it, simply follow this format:

var lazyGreeting = createLazyValue(() => {
    console.debug("Factory function for greeting called");
    return "Greetings";
});

var lazyFarewell = createLazyValue(() => {
    console.debug("Factory function for farewell called");
    return "Farewell";
});

for(var count = 0; count < 4; count++) {
    console.debug(lazyGreeting());
    console.debug(lazyFarewell());
}

The factory function will only execute once, ensuring efficient performance.

Answer 3

Answer №2

To achieve this, you can easily define a Lazy<T> type that functions as a return value with type T. Here's an example:

type Lazy<T> = () => T;

After defining the Lazy<T> type, you have the option to create lazy data structures such as a LazyList implementation which can accommodate an infinite number of elements:

type LazyList<T> = {
   head: Lazy<T>,
   tail: Lazy<LazyList<T>>
} | null

Here, the concept of null indicates an empty list.

Furthermore, you can develop a range function as follows:

function range(min: number = 0, max: number = Infinity) {
   if (max <= min) return null;
   else return {
      head: () => head;
      tail: () => range(min+1, max);
   }
}

This structure of the list resembles that found in Haskell, where each list follows a similar pattern.

Answer 4

To achieve this, you can easily define a Lazy<T> type that functions as a return value with type T. Here's an example:

type Lazy<T> = () => T;

After defining the Lazy<T> type, you have the option to create lazy data structures such as a LazyList implementation which can accommodate an infinite number of elements:

type LazyList<T> = {
   head: Lazy<T>,
   tail: Lazy<LazyList<T>>
} | null

Here, the concept of null indicates an empty list.

Furthermore, you can develop a range function as follows:

function range(min: number = 0, max: number = Infinity) {
   if (max <= min) return null;
   else return {
      head: () => head;
      tail: () => range(min+1, max);
   }
}

This structure of the list resembles that found in Haskell, where each list follows a similar pattern.

How can Lazy<T> be integrated into TypeScript?

Answer №1

Answer №2

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