Subclassing an array and array methods

[Axel Rauschmayer]

Got it, related to what you solve in generic classes with This-types (covariance vs. contravariance...).

    // assume |this| is the source collection
    if (this[Array.derivedArrayKey]) A = this[Array.derivedArrayKey](); else A = [ ];

Another possibility:

    if (this[Array.derivedArrayKey]) {
        A = this[Array.derivedArrayKey]();
    } else if (typeof this.constructor === "function") {
        A = new this.constructor();
    } else {
        A = [ ];
    }

Creating a subclass this way (i.e., using @derivedArrayKey) produces code whose meaning is more obvious (to me) than the code below.

>>> function createArraySubclass(proto,...values) {
>>>   return proto <| [...values].{
>>>         [Array.derivedArrayKey](){return proto<| [ ]}
>>>   }
>>> }

-- 
Dr. Axel Rauschmayer
axel at rauschma.de

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