CoffeeScript: Techniques for Retrieving an Array from a Class

Question

CoffeeScript: Techniques for Retrieving an Array from a Class

Can you identify the issue in this CoffeeScript class?

@module "Euclidean2D", ->
  class @Point
    constructor: (x,y) -> 
      return if Float32Array? then Float32Array([ x, y ]) else Array(x,y)

I would like it to function as follows:

p = new Point(1.0,2.0);
p[0] == 1.0
p[1] == 2.0

However, when testing with Jasmine I am receiving an error message saying "Expected undefined to equal 1."

describe "Point", ->

    beforeEach ->
        @point = new Euclidean2D.Point(1.0,2.0)

    it "extracts values", ->
        (expect @point[0]).toEqual 1.0
        (expect @point[1]).toEqual 2.0

Is the error related to CoffeeScript or Jasmine?

All of the above is wrapped within a module structure like so:

@module = (names, fn) ->
  names = names.split '.' if typeof names is 'string'
  space = @[names.shift()] ||= {}
  space.module ||= @module
  if names.length
    space.module names, fn
  else
    fn.call space

In my Chrome Console output, I see:

a = new Euclidean2D.Point(1.0,2.0)
-> Point
a[0]
undefined
b = new Float32Array([1.0,2.0])
-> Float32Array
b[0]
1

EDIT: Apologies for the confusion.

The issue has been resolved by employing a combination of @brandizzi and @arnaud576875 answers. The @module suggested in the official CoffeeScript Wiki did not yield the desired outcome. The corrected code is:

class @Point
        constructor: (x, y) ->
            return if Float32Array? then Float32Array([ x, y ]) else Array(x,y)

javascript arrays indexing coffeescript

Answer 1

Answer №1

It is recommended to use the new keyword when instantiating the object:

p = new Euclidean2D.Point(1.0,2.0)

If you intend to return an Array from the constructor, be sure to do so explicitly:

constructor: (x,y) -> 
  return if Float32Array? then Float32Array([x,y]) else Array(x,y)

(Coffeescript typically does not automatically return values from the constructor, so additional steps are necessary.)

Another approach that would have worked:

class @Point
  constructor: (x,y) ->
    @[0] = x
    @[1] = y

Answer 2

It is recommended to use the new keyword when instantiating the object:

p = new Euclidean2D.Point(1.0,2.0)

If you intend to return an Array from the constructor, be sure to do so explicitly:

constructor: (x,y) -> 
  return if Float32Array? then Float32Array([x,y]) else Array(x,y)

(Coffeescript typically does not automatically return values from the constructor, so additional steps are necessary.)

Another approach that would have worked:

class @Point
  constructor: (x,y) ->
    @[0] = x
    @[1] = y

Answer 3

Answer №2

Constructors should not be mistaken for regular functions; their purpose is to initialize object values, not return a value. Without setting attributes in the object during initialization, a constructor may lack functionality.

To tackle this issue, consider these suggestions:

Follow @amaud's recommendation and initialize the class.
Rather than returning a value from the constructor, incorporate its functionality within the class itself (option #3 may be more appropriate).
An alternative could be to use a function instead of a class for a simpler, more effective solution:
```
@Point = (x, y) ->
    if Float32Array? then Float32Array([x,y]) else Array(x,y)
```

If you want Point to specialize in either Float32Array or Array, inherit from the desired class using Option #1:

superclass = if Float32Array? then Float32Array else Array  

class @Point extends superclass
  constructor: (x,y) ->
    @[0] = x
    @[1] = y

EDIT: In response to @amaud676875's query, I've developed a CoffeeScript module for further clarification:

class Float32Array extends Array
  first: -> # For testing purposes
    @[0]


superclass = if Float32Array? then Float32Array else Array

class @Point extends superclass
  constructor: (x,y) ->
    @[0] = x
    @[1] = y

After importing the module into the console:

coffee> point = require './point'
{ Point: { [Function: Point] __super__: [ constructor: [Object], first: [Function] ] },
 Float32Array: { [Function: Float32Array] __super__: [] } }

I proceeded to create a new Point:

 coffee> p = new point.Point 3, 2
 [ 3, 2 ]

This Point now possesses the first() method inherited from Float32Array:

 coffee> p.first()
 3

Furthermore, performing an instanceof check confirms that it is indeed an instance of

Float32Array</code:</p>

<pre><code>coffee> p instanceof point.Float32Array
true

In conclusion, executing new Point x, y results in an instance of Float32Array recognized as an instance of Point.

Answer 4

Constructors should not be mistaken for regular functions; their purpose is to initialize object values, not return a value. Without setting attributes in the object during initialization, a constructor may lack functionality.

To tackle this issue, consider these suggestions:

Follow @amaud's recommendation and initialize the class.
Rather than returning a value from the constructor, incorporate its functionality within the class itself (option #3 may be more appropriate).
An alternative could be to use a function instead of a class for a simpler, more effective solution:
```
@Point = (x, y) ->
    if Float32Array? then Float32Array([x,y]) else Array(x,y)
```

If you want Point to specialize in either Float32Array or Array, inherit from the desired class using Option #1:

superclass = if Float32Array? then Float32Array else Array  

class @Point extends superclass
  constructor: (x,y) ->
    @[0] = x
    @[1] = y

EDIT: In response to @amaud676875's query, I've developed a CoffeeScript module for further clarification:

class Float32Array extends Array
  first: -> # For testing purposes
    @[0]


superclass = if Float32Array? then Float32Array else Array

class @Point extends superclass
  constructor: (x,y) ->
    @[0] = x
    @[1] = y

After importing the module into the console:

coffee> point = require './point'
{ Point: { [Function: Point] __super__: [ constructor: [Object], first: [Function] ] },
 Float32Array: { [Function: Float32Array] __super__: [] } }

I proceeded to create a new Point:

 coffee> p = new point.Point 3, 2
 [ 3, 2 ]

This Point now possesses the first() method inherited from Float32Array:

 coffee> p.first()
 3

Furthermore, performing an instanceof check confirms that it is indeed an instance of

Float32Array</code:</p>

<pre><code>coffee> p instanceof point.Float32Array
true

In conclusion, executing new Point x, y results in an instance of Float32Array recognized as an instance of Point.

CoffeeScript: Techniques for Retrieving an Array from a Class

Answer №1

Answer №2

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