Use private instead of protected visibility #1019
Description
In Magento 1, class properties and methods are all defined with public or protected visibility. In PHP, changing the API of a protected property or method usually constitutes a backwards compatibility break. Have Magento considered using private instead of protected visibility as the default alternative to public in Magento 2?
Consider the following examples:
namespace Magento;
// version 1.0
class Product
{
protected function somethingInternal() {}
}namespace SomeThirdParty;
class MyProduct extends \Magento\Product
{
public function somethingPublic()
{
// ...
parent::somethingInternal();
// ...
}
}namespace SomeOtherThirdParty;
class MyProduct extends \Magento\Product
{
public function someCoolNewMethod() {}
}namespace Magento;
// version 1.1
class Product
{
// this breaks SomeThirdParty\MyProduct
protected function somethingInternal($newParam) {}
// this breaks SomeOtherThirdParty\MyProduct
protected function someCoolNewMethod($requiredParam) {}
}The above examples demonstrate how adding or modifying protected methods can break downstream packages. If those methods had been declared private, re-factoring would have been fine without any BC issues.
Why use protected by default? Presumably it's 'just in case' someone downstream wants to replace or re-use a piece of functionality. The thing to understand is that protected comes with a cost; it essentially means you can't do any re-factoring. If a piece of functionality is really worth exposing then why isn't it public?