PHP 5.5 First Look
Illustration by Don Barnett

Simple iterators using generators


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PHP 5.5 First Look

with Jon Peck

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Video: Simple iterators using generators

One of the most common programming needs, is to be able to perform an action on every element of an object. For example, using a foreach on an array, to get each key in value, or a foreach on a standard object, to get each parameter name and value. The mechanism for implementing this behavior is known as an iterator, which is used for traversing through all elements of an object or an array. Iterators can be explicitly defined for custom classes, but that can be an unwieldy and complicated process involving implements and, more than a handful of functions.
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Watch the Online Video Course PHP 5.5 First Look
42m 29s Intermediate Jun 14, 2013

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Join author Jon Peck as he demonstrates new functionality in PHP 5.5, including generators, the try-catch-finally execution model, and a brand-new password hashing API. A number of existing behaviors, such as the foreach() and empty() functions, have also been updated, and Jon explores what changed and how it can be used. Throughout this course, you'll learn to add new functionality to a simple deck of cards class using these new and updated features, and how to use them for the basis of your own project.

Topics include:
  • Using generators to create simple iterators
  • Dereferencing strings and arrays
  • Enhancing security with the password hashing API
  • Replacing APC with OPcache
  • Normalizing Boolean and unpack() behavior
  • Surveying the removed, incompatible, and deprecated functionality
Subject:
Developer
Software:
PHP
Author:
Jon Peck

Simple iterators using generators

One of the most common programming needs, is to be able to perform an action on every element of an object. For example, using a foreach on an array, to get each key in value, or a foreach on a standard object, to get each parameter name and value. The mechanism for implementing this behavior is known as an iterator, which is used for traversing through all elements of an object or an array. Iterators can be explicitly defined for custom classes, but that can be an unwieldy and complicated process involving implements and, more than a handful of functions.

What if I want to act on a subset of an array, and perform some logic as I go along, but still be able to iterate through the object? Well, PHP 5.5 has introduced generators, which are an easy oilerplate free way, of implementing an iterator by using the special yield keyword. Yield provides a value to codes looping over the generator, and pauses the generator function execution. It'll look very similar to return statement. I'm going to use a generator to draw cards from a deck. I'm going to switch the IDE, navigate to Classes and open Game.php.

I'm going to code a public function draw cards. This function takes one argument, which is the number of cards to draw. I'm going to start with some simple logic. So if, number of cards not equals intval number of cards, because you can only have whole cards, throw new Exception, cannot take partial cards. Now that I have that out of the way, I am going to use the number of cards as part of a for loop. For count equals 0, count is less then the number of cards, and count ++. I'm going to get the cards from the deck, so cards equal this. Deck, get cards.

If there are any, recycle the deck, meaning put the discard in the deck and shuffle. So if, empty, cards, this, recycle. At the end of the loop, I'm going to yield a drawn card. This means each time it goes through the loop, it'll generate a drawn card. Yield, this_deck, draw. Save and navigate to the construct above. I'm doing a foreach for the number of players and cards per player, and putting each card yielded by the generator in the hand.

To see this in action, switch to the browser and click on Game. The deck, discard, and two players are rendered with their drawn cards.

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Q: How do I import the php55.sql file into MySQL?
A: Copy the php55.sql file from the Exercise Files folder to somewhere you can access it at the command line. (In this course, that's the 'sandbox' folder.)
 
Then type:
mysql -user=sandbox -password=sandbox sandbox < php55.sql
 
Be sure to substitute your MySQL username and password if necessary.
 
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