Utilizing typed arrays within generic functions

Within a library, there exists a helper function designed to work with arrays of any type. The next step is to expand its functionality to also accommodate typed arrays. However, the challenge lies in the absence of a common base class for typed arrays or generic options. Below is the current code snippet tailored for generic arrays and one specific typed array:

    public static copyOf(original: Int32Array, newLength: number): Int32Array;
    public static copyOf<T>(original: T[], newLength: number): T[];
    public static copyOf<T>(original: T[] | Int32Array, newLength: number): T[] | Int32Array {
        if (original instanceof Int32Array) {
            if (newLength < original.length) {
                return original.slice(0, newLength);
            }

            if (newLength === original.length) {
                return original.slice();
            }

            const result = new Int32Array(newLength);
            result.set(original);

            return result;

        } else {
            if (newLength < original.length) {
                return original.slice(0, newLength);
            }

            if (newLength === original.length) {
                return original.slice();
            }

            const result = new Array<T>(newLength);
            result.splice(0, 0, ...original);

            return result;
        }
    }

The above approach necessitates individual branches for each type of typed array, which deviates from the concept of generics. Is there a more succinct way to implement this without branching out for every typed array type?

Answer №1

When it comes to TypeScript and typings, there isn't a predefined type for typed arrays as of now. You can create your own custom type using a union of the relevant individual types. Here's an example:

type TypedArray = Int8Array | Uint8Array | Int16Array | Uint16Array | Int32Array |
  Uint32Array | Uint8ClampedArray | Float32Array | Float64Array;

For implementation, you can utilize the constructor property of the typed array passed in to get the correct class constructor and build a new instance from it. Although TypeScript doesn't fully support strongly-typed constructor properties, you can use a type assertion to make it work.

A possible implementation could look something like this:

// Implementation code here

In this implementation, I've used Array.isArray() instead of instanceof to verify that the value is not a built-in array.

To confirm its functionality, testing with different examples would be essential:

// Test cases and results go here

Everything seems to be working fine based on the test results.

Try out the code on TypeScript playground

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