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@kingjs/enumerable.define

Defines a function that returns an Enumerable.

Usage

Define an Enumerable that generates a finite number of clock ticks and then use it to generate 3 ticks like this:

var define = require('@kingjs/enumerable.define');

var currentTicks = define(

  function generatorFactory(tickCount) {

    return function generator() {
      if (tickCount <= 0)
        return false;
      tickCount--;

      // ensure at a tick elapses between generations
      if (this.current_) {
        while (this.current_ == Date.now())
          ;
      }

      this.current_ = Date.now();
      return true;
    }
  }
);

var enumerable = currentTicks(3);
var enumerator = enumerable.getEnumerator();

var result = [];
while (enumerator.moveNext())
  result.push(enumerator.current);

result;

Result is something like this:

[
  1534412527360,
  1534412527361,
  1534412527362
]

Interfaces Enumerable & Enumerator

declare interface Enumerable {
  getEnumerator(): Enumerator
}  

declare interface Enumerator {
  moveNext(): boolean,
  current
}  

An Enumerable is a sequence of lazily generated values. To enumerate the values in an Enumerable, first call getEnumerator to get an Enumerator, and then call moveNext on the Enumerator.

If moveNext returns true, then a value has been generated and can be accessed via current. Subsequent calls to moveNext which return true generate subsequent values which can be accessed via current.

If moveNext returns false, then all values have been generated and current returns undefined. At this point subsequent calls to moveNext will continue to return false and current will continue to return undefined.

API

declare function define(
  generatorFactory: (...args: any[]) => 
      (this: { current_ }) => boolean
): (...args: any[]) => Enumerable

Parameters

• generatorFactory: A function that returns a generator function closed over args. The function generator is called when moveNext is called and should either assign a freshly generated value to this.current_ and return true or, if no more values remain to be generated, return false.

Return Value

Returns a function which takes arbitrary parameters args and returns an Enumerable whose values are generated by calls to a generator created by generatorFactory using args.

Remarks

A generator may assume that after it returns false the scaffolding:

• Will set this.current_ to undefined.
• Will prevent subsequent invocations.

The generatorFactory will be invoked upon the first call to moveNext with the this and the arguments passed to the function returned by define.

More Remarks

Enumerator is similar in functionality to Javascript's Iterator pattern but is more memory efficient. Iterator requires creation of a wrapper object (e.g. { value: 'someGeneratedValue' }) for every generated value but Enumerable returns the value directly from current.

Install

With npm installed, run

$ npm install @kingjs/enumerable.define

Acknowledgments

Like the boilerplate types generated by C# yield syntax.

License

MIT