TypeScript: Defining an Array Type within a Namespace or Module

Question

TypeScript: Defining an Array Type within a Namespace or Module

Within a specific namespace, I have the following code:

    const operation1 = Symbol("operation1");
    const operation2 = Symbol("operation2");

    export interface Array<T> extends IConjable<T>, ISeqable<T> {}

    Array.prototype[operation1] = function<X>(x: X) {
        this.push(x);
        return this;
    };

    Array.prototype[operation2] = function() {
        return new ArraySequence(this, 0);
    };

However, when running this code, I encountered an error message stating:

src/seq2.ts:497:21 - error TS7015: Element implicitly has an 'any' type because index expression is not of type 'number'.

497     Array.prototype[operation1] = function<X>(x: X) {
                        ~~~~~~~~~~~

src/seq2.ts:502:21 - error TS7015: Element implicitly has an 'any' type because index expression is not of type 'number'.

502     Array.prototype[operation2] = function() {

Furthermore, there were additional issues with expressions like particularArray[pointer], resulting in errors such as:

src/seq2.ts:430:40 - error TS2339: Property 'length' does not exist on type 'Array<X>'.

430         condition && variable && ptr < this.array.length;
                                           ~~~~~~

src/seq2.ts:433:23 - error TS7017: Element implicitly has an 'any' type because type 'Array<X>' has no index signature.

433         condition = hd === this.array[ptr];
                          ~~~~~~~~~~~~~~~

The resolution to these errors was achieved by removing the namespace.

arrays typescript

Answer 1

Answer №1

When enhancing the functionality of Array, it is important to always do so in the global scope. By defining

export interface Array<T> extends IConjable<T>, ISeqable<T> {}

within a namespace, you are not actually improving the array itself but rather creating a new interface named Array. Consequently, the global Array constructor would still refer to the original array without enhancements.

If you wish to organize the code within a namespace, ensure that the augmentation remains at the top level:

interface Array<T> extends X.IConjable<T>, X.ISeqable<T> { }
namespace X {
    const conj_method = Symbol("conj_method");
    const toSeq_method = Symbol("toSeq_method");

    export interface IConjable<T> { [conj_method](x: T): this }
    export interface ISeqable<T> { [toSeq_method](x: T): this }

    Array.prototype[conj_method] = function <X>(x: X) {
        this.push(x);
        return this;
    };

    Array.prototype[toSeq_method] = function () {
        return new ArraySeq(this, 0);
    };
}

The provided example caters to script files and non-modules (i.e., files lacking top-level export or import). To enable augmentation within a module, it is necessary to place the Array enhancement on a global scale:

declare global {
    interface Array<T> extends X.IConjable<T>, X.ISeqable<T> { }    
}

Answer 2

When enhancing the functionality of Array, it is important to always do so in the global scope. By defining

export interface Array<T> extends IConjable<T>, ISeqable<T> {}

within a namespace, you are not actually improving the array itself but rather creating a new interface named Array. Consequently, the global Array constructor would still refer to the original array without enhancements.

If you wish to organize the code within a namespace, ensure that the augmentation remains at the top level:

interface Array<T> extends X.IConjable<T>, X.ISeqable<T> { }
namespace X {
    const conj_method = Symbol("conj_method");
    const toSeq_method = Symbol("toSeq_method");

    export interface IConjable<T> { [conj_method](x: T): this }
    export interface ISeqable<T> { [toSeq_method](x: T): this }

    Array.prototype[conj_method] = function <X>(x: X) {
        this.push(x);
        return this;
    };

    Array.prototype[toSeq_method] = function () {
        return new ArraySeq(this, 0);
    };
}

The provided example caters to script files and non-modules (i.e., files lacking top-level export or import). To enable augmentation within a module, it is necessary to place the Array enhancement on a global scale:

declare global {
    interface Array<T> extends X.IConjable<T>, X.ISeqable<T> { }    
}

TypeScript: Defining an Array Type within a Namespace or Module

Answer №1

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