CoffeeScript Dynamic Methods

Question

I am trying to dynamically create methods in a coffee script, but, as my code shows, the iterator that I use to create methods does not reset its variables between iterations, so I fit into common variables that have conflicts:

class MyClass constructor: (@name) -> for k, v of ['get', 'set'] console.log('creating method: ' + v) MyClass::[v] = (args...) -> method = v console.log('executing method: ' + method) o = new MyClass('dummy') o.get() o.set() 

Outputs:

 > creating method: get > creating method: set > executing method: set > executing method: set 

Does anyone know what I'm doing wrong?

Answer 1

Your internal function:

 (args...) -> method = v console.log('executing method: ' + method) 

is actually a closure on v , so when it is executed, v will evaluate its last value in the loop (i.e. set ). Looks like you just need to sort out the closure a bit:

 build_method = (v) -> (args...) -> method = v console.log('executing method: ' + method) 

And then:

 for k, v of ['get', 'set'] console.log('creating method: ' + v) MyClass::[v] = build_method(v) 

Keep in mind that CoffeeScript is just JavaScript with a different make-up, so it experiences a lot of problems (like any language with closure), and these problems have the same solutions.

Answer 2

mu correctly diagnosed the problem. The most immediate solution is to use the do keyword for the CoffeeScript language, which creates and runs an internal function that captures the values ​​of the variables you pass in:

 for k, v of ['get', 'set'] do (k, v) -> console.log('creating method: ' + v) MyClass::[v] = (args...) -> method = v console.log('executing method: ' + method) 

I will talk about this feature in my PragPub article, A CoffeeScript Intervention .