.value functions should not be observable

[justinbmeyer]

If they are observable and invoked as part of a template, big problems can happen.

The solution is just to make sure

1. Observation.add should not be called if this.__inSetup is true: https://github.com/canjs/can-construct/blob/master/can-construct.js#L280

2. We should wrap value with Observation.ignore.

[justinbmeyer]

http://jsbin.com/yafajal/edit?html,js,output

Also related ... we should check the number of dependencies in the observation.

[justinbmeyer]

Also, we can probably avoid .getCurrent() if this.__inSetup is true: https://github.com/canjs/can-define/blob/master/can-define.js#L280

here: canjs/can-reflect#2

[justinbmeyer]

var DriversListVM = can.DefineMap.extend({
  drivers: {
    value: function(){
      return new can.DefineList([
        { title: "Dr.", first: "Cosmo", last: "Kramer", licensePlate: "A$$M^N" },
        { title: "Ms.", first: "Elaine", last: "Benes", licensePlate: "621433" }
     ])
    }
  },
  selected: {
    value: false
  },
  select: function(driver){
    this.selected = driver;
  }
})

var func = function(){};

func = Observation.ignore(func);

func();

[justinbmeyer]

return function(newVal) {
  if( this._inSetup ) {
    setData.call(this, newVal);
  } else {

	var current = getCurrent.call(this);
	if (newVal !== current) {
	  setData.call(this, newVal);

	canEvent.dispatch.call(this, {
						type: prop,
						target: this
	  }, [newVal, current]);
	}
  }
}

[justinbmeyer]

https://github.com/canjs/can-define/blob/master/can-define.js#L178

getInitialValue = Observation.ignore( make.get.defaultValue(prop, definition, typeConvert, eventsSetter) );

[bmomberger-bitovi]

It turns out we couldn't avoid getCurrent because that was responsible for executing the getter applied by replaceWith before trying to set the value. However, that doesn't mean that we can't Observation.ignore it.