gistfile1.txt

Let's say you have this:

class SomeClass
{
  // users are encouraged to extend and set to true to enable magical powers...
  protected $someQuality = false;
  
  public function isSomeQuality()
  {
     return $this->someQuality;
  }
}

and want to use this:

trait SomeTrait
{
  protected $someQuality = true;
  
  // useful stuff based upon that difference...
}

like this:

class SomeExtendedCLass extends SomeClass
{
  use SomeTrait;
}

You can't, you'll get a Fatal Error for redeclaring the member variable with a different initialized value.

Instead, you're forced to do this:

trait SomeTrait
{
  public function isSomeQuality()
  {
    return true; // eww! Especially considering that $someQuality == false.
  }
  
  // useful stuff based upon that difference...
}

when had the original class author done this:

class SomeClass
{
  public function isSomeQuality()
  {
     return $this->someQuality ?? false;
  }
}

leaving $someQuality undeclared, everyone would be better off.