Adds can.Compute, and "compute" type and setter / getter paring for define pugin

[justinbmeyer]

You can:

c = new can.Compute(5);
c.get()
c.set(6)
c.bind("change", callback)

MyMap = can.Map.extend({
  define: {value: {type: "compute"} }
})
var myMap = new MyMap();
var c = can.compute(5);

myMap.attr("value",c);
myMapp.attr("value") //-> 5

c(6)
myMapp.attr("value") //-> 6

var c2 = can.compute("a")
myMap.attr("value",c2);
myMapp.attr("value") //-> "a"

MyMap = can.Map.extend({
  define: {
    num: {
      set: function(newValue){
        return +newValue;
      },
      get: function(lastSetValue){
        return Math.pow( lastSetValue, this.attr("pow") )
      }
    }
  }
})

var myMap = new MyMap({pow: 2});
myMap.attr("num","4");
myMap.attr("num") //-> 16

[justinbmeyer]

@daffl I'm assigning this to you as this might break a few of the compute.async tests. You can probably comment them out in the legacy tests b/c they aren't a documented API.

[akagomez]

From the looks of it, this is now possible too:

can.define.powerOfTwo = {
  set: function(newValue){
    return +newValue;
  },
  get: function(lastSetValue){
    return Math.pow( lastSetValue, 2)
  }
}

MyMap = can.Map.extend({
  define: {
    num: {
      type: 'powerOfTwo'
    }
  }
})

var myMap = new MyMap();
myMap.attr("num","4");
myMap.attr("num") //-> 16

[daffl]

How is this supposed to work? For some reason it is only breaking for Mootools but can.proxy(true, internalCompute) doesn't seem right.

[justinbmeyer]

isComputed is a boolean. So I think this should be compute.isComputed = true

[akagomez]

In my playing with this branch I noticed that isComputed was no longer a boolean and was uber confused. Glad that's cleared up.