What’s New in PHP 5.5

PHP 5.5 was recently released, introducing several exciting new features to the language. In this article, we’ll go through some of the most interesting additions and discuss the benefits they provide to developers.

Generators

Generators are one of the most eagerly anticipated new features. They provide a way to handle iteration without having to write a class that implements the Iterator interface. Making a class conform to the Iterator interface requires a substantial amount of boilerplate code, so being able to avoid this by using generators can significantly reduce the size and complexity of code that developers must write.

Generators derive their functionality from the new yield keyword. A generator looks very similar to a normal function, but instead of returning a single value, a generator may yield any number of values.

To properly illustrate the power of generators, an example is needed. Consider PHP’s range() function, which returns an array of the values between the $start and $end arguments. We can use range() as follows:

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<?php
foreach (range(0, 1000000) as $number) {
    echo $number;
}

The problem in this example is that the array returned by range() will occupy a lot of memory (over 100mb according to the PHP manual). While the above code is a trivial demonstration, there are plenty of real-world situations where large arrays of data are constructed, often taking a long time to build and occupying a lot of memory.

With the introduction of generators, it’s now easy to tackle this problem without the inconvenience of having to write an Iterator class. Generators do not construct a large array, but rather return a single element at a time as they are iterated. Consider this modification to the above code, now using a generator to produce the range of values:

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<?php
// define a simple range generator
function generateRange($start, $end, $step = 1) {
    for ($i = $start; $i < $end; $i += $step) {
        // yield one result at a time
        yield $i;
    }
}

foreach (generateRange(0, 1000000) as $number) {
    echo $number;
}

This code produces exactly the same result as the first example, but without producing a large array to store all the values. According to the manual, this reduces the memory footprint to less than a single kilobyte – a huge saving compared with the original example.

Password Hashing

The new password hashing API is one of the most important and useful features added in PHP 5.5. In the past, developers have had to rely on the somewhat confusing crypt() function, which is poorly documented in the PHP manual. The introduction of a simplified set of functions to handle password hashing will make it much easier for developers to understand and implement secure password hashing for their sites.

The new API introduces two new functions, password_hash() and password_verify(). Calling password_hash($password, PASSWORD_DEFAULT) will return a strong hash using bcrypt, with salting handled automatically. Verifying the password later is as easy as checking the result of password_verify($password, $hash).

The API uses bcrypt by default, but in the future new algorithms may be introduced to provide even more secure methods of hashing. Developers can specify their own bcrypt work factor to adjust the strength of the hashes produced, and can also use their own salts instead of the automatic salt generation (although the manual discourages this).

finally

PHP 5.5 adds support for the finally keyword, a much-requested feature found in many other languages with exception handling. finally allows developers to specify code to be run at the end of try and catch blocks, regardless of whether an exception was thrown or not, before the normal execution flow resumes.

Without the finally keyword, developers were sometimes be forced to repeat code within both the try and catch blocks to handle cleanup tasks. For example, in the following example the call to releaseResource() must be made in two places:

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<?php
function doSomething() {
    $resource = createResource();
    try {
        $result = useResource($resource);
    }
    catch (Exception $e) {
        releaseResource($resource);
        log($e->getMessage());
        throw $e;
    }
    releaseResource($resource);
    return $result;
}

With the addition of finally, we can eliminate the duplicate code:

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<?php
function doSomething() {
    $resource = createResource();
    try {
        $result = useResource($resource);
        return $result;
    }
    catch (Exception $e) {
        log($e->getMessage());
        throw $e;
    }
    finally {
        releaseResource($resource);
    }
}

In the modified version, we call the cleanup function releaseResource() in the finally block where we know it will always be called. Note that even though the try block returns a value, the finally block will still be called before the return statement is executed and normal execution continues.

Array and String Literal Dereferencing

Array and string literals can now be dereferenced using array access syntax:

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<?php
// array dereferencing - returns 3
echo [1, 3, 5, 7][1];

// string dereferencing - returns "l"
echo "hello"[3];

This feature was added primarily to improve the consistency of the language, and probably won’t revolutionize the way we write PHP. However, there are some interesting applications to consider, such as the following:

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<?php
$randomChar = "abcdefg0123456789"[mt_rand(0, 16)];

Using empty() with Function Calls and Expressions

The empty() construct can now be used with function calls and other expressions. For example, empty($object->getProperty()) is valid code in PHP 5.5. This makes it possible to use empty() on the return value of functions without capturing the value in a variable first.

Class Name Resolution

Since the introduction of namespaces in PHP 5.3, it has become common practice to use extensive namespacing to organize classes in PHP projects. However, until now it has been difficult to retrieve a fully-qualified class name as a string. Consider the following code:

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<?php
use NamespacedClassFoo;

$reflection = new ReflectionClass("Foo");

This will fail as PHP will attempt to use the global Foo class instead of the namespaced class. In PHP 5.5, it is now possible to retrieve the full namespaced class name as a string using the class keyword:

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<?php
use NamespacedClassFoo;

$reflection = new ReflectionClass(Foo::class);

This will now work as intended, as Foo:class will resolve to Namespaced\Class\Foo.

Changes to foreach

The list() construct in PHP allows the values of an array to be easily assigned to variables. For example:

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<?php
$values = ["sea", "blue"];

list($object, $description) = $values;

// returns "The sea is blue"
echo "The $object is $description";

It’s now possible to use list() with multidimensional arrays within foreach loops. For example:

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<?php
$data = [
    ["sea", "blue"],
    ["grass", "green"]
];

foreach ($data as list($object, $description)) {
    echo "The $object is $descriptionn";
}/* Outputs:
The sea is blue
The grass is green
*/

This is a powerful new feature that has the potential to make iterating through nested arrays much easier and cleaner.

foreach loops can now also handle non-scalar values as iterator keys, which means that element keys may have values that are not strings or integers.

Conclusion

PHP 5.5 offers many improvements to facilitate PHP development. In addition to new features, a long list of bugs have been resolved in this release (see the changelog for details), and various optimizations and enhancements have been made to improve performance and stability.

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