Feathers and Weights

Taking the feathers and weights from plucking chickens its time to add them up. Lets take a look at how to convert a for-loop to a reusable functional solution.

var feathersPerChicken:Array = pluck(chickens, "feathers"); // Array of Numbers
var weightsPerChicken:Array = pluck(chickens, "weight"); // Array of Numbers

The basic for-loop to add up the number of feathers looks like this:

var totalFeathers:Number = 0;
for (var i:int = 0, n:int = feathersPerChicken.length; i < n; i++) {
  totalFeathers += feathersPerChicken[i];
}

As this loop iterates over every item in the Array we can simply replace it with a Array.forEach

var totalFeathers:Number = 0;
feathersPerChicken.forEach(function(numberOfFeathers:Number, i:int, a:Array) {
  totalFeathers += numberOfFeathers;
});

Instead of manually managing the iterator index i and length n, Array.forEach does that work. However in its place we have to declare an anonymous function to close over the scope of totalFeathers and add to that variable the numberOfFeathers. There is still a lot of boilerplate code in that block that could be removed or hidden as it is not helping us understand what the code is doing.

For the next steps lets replace the for loop and Array.forEach with a function call for what the intention of the code is: adding up a bunch of numbers, or rather getting the sum.

var totalFeathers:Number = sum(feathersPerChicken);

Now that is much clearer.

Implementing sum could be as simple as wrapping up the previous example into a sum function. It could then be used to add up the weights of the chickens too.

function sum(numbers:Array):Number {
  var total:Number = 0;
  numbers.forEach(function(number:Number, i:int, a:Array):void {
    total += number;
  });
}

var totalFeathers:Number = sum(feathersPerChicken);
var totalWeight:Number = sum(weightPerChicken);

By replacing the for loops from the original example the code is now much easier to read, and tells exactly what its doing. A couple of more subtle gains from this are the scope is kept clean of temporary variables, and there is now a hook to change how the total is calculated without affecting the signature of the sum function.

sum() is available in asx and implemented using a number of other helpful functions: inject and add.