Is this a 'proper' use of a trait in PHP?

Question

In Laravel 5.6 an Illuminate\Database\Eloquent\Relations\BelongsTo relation was given the ability to support default models. This allows a model that will be returned if the relationship is empty.

Most of the code for doing this lives in the Illuminate\Database\Eloquent\Relations\Concerns\SupportsDefaultModels trait, which the BelongsTo relation uses.

Here's an example of a method in the relation calling the getDefaultFor method from the trait:

/**
 * Get the results of the relationship.
 *
 * @return mixed
 */
public function getResults()
{
    return $this->query->first() ?: $this->getDefaultFor($this->parent);
}

The getDefaultFor method only exists in the trait. It's not defined on the class itself. For some reason I was always under the impression that this is not 'proper'. In other words, if I were to remove the trait, the class would break. Shouldn't the class have some sort of fallback getDefaultFor method defined on it that the trait can override?

I realize this is an extremely nitpicky question and doesn't really matter since the code works, but I am just trying to understand from a code design perspective if this is the proper way to do things.

Does anyone have any thoughts on this?

Answer 1

Far from being an expert, but I had the same question in mind for a while as well. This is what I have gathered.

• The generic (across languages) definition does emphasize that a trait can extend the functionality of a class. So if added to a class, the class indeed would not work without it.
• There is no clear consensus on it in the community (for instance), even though it was a core addition to php 5+.
• Just about every search package for Laravel is a trait and therefore the controller heavily depends on it without a fallback.
• Laravel's own code often makes idiosyncratic uses of patterns, such as their Facades, but it's one of those cases of where the 800-pound elephant sits wherever it wants.

In my own code, I use traits for common operations, like string manipulation. Traits seem to be fancy ways to avoid copy and paste of functions that don't need classes.

Just my amateur opinion.