Overriding Doctrine Trait Properties

问题:

I know you can override a trait method by declaring it in your class, I was curious if was possible to over ride a trait Property the same way. Is this safe to do? Its not in the Documentation so I am hesitant to implement this.

From the Documentation

An inherited member from a base class is overridden by a member inserted by a Trait. The precedence order is that members from the current class override Trait methods, which in turn override inherited methods.

http://php.net/manual/en/language.oop5.traits.php

回答1:

You cannot override a trait's property in the class where the trait is used. However, you can override a trait's property in a class that extends the class where the trait is used. For example:

trait ExampleTrait
{
    protected $someProperty = 'foo';
}

abstract class ParentClass
{
    use ExampleTrait;
}

class ChildClass extends ParentClass
{
    protected $someProperty = 'bar';
}

回答2:

My solution was to use the constructor, example:

trait ExampleTrait
{
    protected $someProperty = 'foo';
}

class MyClass
{
    use ExampleTrait;

    public function __construct()
    {
         $this->someProperty = 'OtherValue';
    }
}

回答3:

An alternative solution, in this case using the property updatable.

I use this when the property is only required within the trait's methods...

trait MyTrait
{
    public function getUpdatableProperty()
    {
        return isset($this->my_trait_updatable) ?
            $this->my_trait_updatable:
            'default';
    }
}

...and using the trait in a class.

class MyClass
{
    use MyTrait;

    /**
     * If you need to override the default value, define it here...
     */
    protected $my_trait_updatable = 'overridden';
}

回答4:

You can declare a trait property in a class but you must keep the same definition from the trait. It couldn't be overridden with different definition. So, as you already has access to trait properties from class, it's not needed to redefined again. Think that a trait works as a copy paste code.

<?php
trait FooTrait 
{
    protected $same       = '123';
    protected $mismatch  = 'trait';
}

class FooClass 
{
    protected $same      = '123';

    // This override property produces: 
    // PHP Fatal error:  FooClass and FooTrait define the same property
    // ($mismatchValue) in the composition of FooClass. However, the definition
    // differs and is considered incompatible
    protected $mismatch  = 'class';

    use FooTrait;
}