@stamp/fp-constructor

• Adds the Stamp.of static property referencing Stamp itself
• Adds the instance.constructor property referencing Stamp itself

By composing the @stamp/fp-constructor into your stamp

MyStamp = MyStamp.compose(FpConstructor);

you get the static method .of:

MyStamp.of === MyStamp; // true

and the instance method, .constructor:

instance = MyStamp(/* ...options */);
instance.constructor === MyStamp; // true

Motivation

Frequently, it's desirable to instantiate a new instance of a given datatype inside a generic function. However, JavaScript lacks a built-in way to do that which is reliable. Classes throw errors if you leave off new, and arrow function factories will throw if you try to instantiate an instance with new, and there's no standard way to inject a value into the new datatype.

The Stamp.of() is a standard way to create a new value of a given stamp where the calling conventions are unambiguous: It does not require new, and you inject the value by passing the necessary arguments directly into the .of() static method.

Having the .of() method only solves half of the problem, though. You still need a way got get a handle on the stamp from an object instance. You can do that with the instance.constructor() method.

Here's an example of what you can do with the combination. The following empty() utility will return an empty instance of whatever supporting datatype you pass in, including standard JavaScript arrays:

const empty = ({ constructor } = {}) => constructor.of ?
  constructor.of() :
  undefined
;

const foo = [23];

console.log(
  empty(foo) // []
);

All applicative functors in JavaScript should implement .of().

Usage

import FpConstructor from '@stamp/fp-constructor';

MyStamp = MyStamp.compose(FpConstructor);

API

Static methods

methods

stamp.of(...args) => Object

Instance methods

methods

instance.constructor(...args) => Object