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    <blockquote> <p><em>An often used metaphor to describe Traits is Traits are interfaces with implementation.</em></p> </blockquote> <p>This is a good way of thinking about it in most circumstances, but there are a number of subtle differences between the two.</p> <p>For a start, the <code>instanceof</code> operator will not work with traits (ie, a trait is not a real object) so you can't us that to see if a class has a certain trait (or to see if two otherwise unrelated classes share a trait). That's what they mean by it being a construct for horizontal code re-use.</p> <p>There <em>are</em> functions now in PHP that will let you get a list of all the traits a class uses, but trait-inheritance means you'll need to do recursive checks to reliably check if a class at some point has a specific trait (there's example code on the PHP doco pages). But yeah, it's certainly not as simple and clean as instanceof is, and IMHO it's a feature that would make PHP better.</p> <p>Also, abstract classes are still classes, so they don't solve multiple-inheritance related code re-use problems. Remember you can only extend one class (real or abstract) but implement multiple interfaces.</p> <p>I've found traits and interfaces are really good to use hand in hand to create pseudo multiple inheritance. Eg:</p> <pre><code>class SlidingDoor extends Door implements IKeyed { use KeyedTrait; [...] // Generally not a lot else goes here since it's all in the trait } </code></pre> <p>Doing this means you can use instanceof to determine if the particular Door object is Keyed or not, you know you'll get a consistent set of methods etc, and all the code is in one place across all the classes that use the KeyedTrait.</p>
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    1. POTraits vs. Interfaces
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    1. COThe last part of that answer is of course what @rdlowrey is saying in more detail in the last three paragraphs under "Traits" in his post; I just felt a really simple skeleton code snippet would help to illustrate it.
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    2. COI think the best OO way to use traits is using interfaces where you can. And if there is a case when multiple subclasses implementing the same kind of code for that interface and you can't move that code to their (abstract) superclass -> implement it with traits
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