ocramius/lazy-property

A library that provides lazy instantiation logic for object properties

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Dependents: 1

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Watchers: 3

Forks: 1

Language: PHP

1.0.0 2014-02-19 16:24 UTC

README

This small library aims at providing a very simple and efficient loading of lazy properties

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Installation

The suggested installation method is via composer:

php composer.phar require ocramius/lazy-property:1.0.*

Use case

In many cases where lazy-initialization of private/protected properties is necessary, many people write classes that look like following:

class SomeService
{
    protected $dependency;

    public function doWork()
    {
        $this->getDependency()->delegateWork();
    }

    protected function getDependency()
    {
        return $this->dependency ?: $this->dependency = get_dependency_somehow();
    }
}

This is problematic because implementors and people subclassing SomeService will eventually write:

class SomethingElse extends SomeService
{
    public function doOtherWork()
    {
        $this->dependency->doMoreWork();
    }
}

This can work only if SomeService#getDependency() was called at least once upfront (which may well be under certain circumstances), and therefore is a cause of bugs/headaches/suicides/etc.

In order to avoid this problem, the implementor of SomeService that is also exposing its protected $dependency property may just use LazyProperty\LazyPropertiesTrait to fix the problem:

class SomeService
{
    use \LazyProperty\LazyPropertiesTrait;

    protected $dependency;

    public function __construct()
    {
        $this->initLazyProperties(['dependency']);
    }

    public function doWork()
    {
        // look ma! no getter!
        $this->dependency->delegateWork();
    }

    protected function getDependency()
    {
        return $this->dependency ?: $this->dependency = get_dependency_somehow();
    }
}

With this, any access to SomeService#$dependency will cause a call to SomeService#getDependency() if the property was not already initialized.

class SomethingElse extends SomeService
{
    public function doOtherWork()
    {
        // always works
        $this->dependency->doMoreWork();
    }
}

Please note that a getter is required in order for the property to be lazy.

Performance notes

Using LazyProperty\LazyPropertiesTrait allows to speed up applications where a massive amount of getter calls is going on in private/protected scope. There is some minor overhead in calling SomeService#initLazyProperties(), as well as in the first property access, but it should be negligible.