Setters with a default value are a bit odd: I want to set a value, but I won't tell you which one!

We do have this kind of setters, like this example fromTokenStorageInterface:

publicfunction setToken(TokenInterface$token =null);

This means that those to calls are equivalent:

$tokenStorage->setToken(null);$tokenStorage->setToken();

The reason for this is actually a php 5 quirk: On php 5, we did not have nullable parameter type declarations – those we added in php 7.1. The only workaround was to declarenull as default value because then php would accept passing null despite the type declaration demanding an instance of a specific class/interface.

Because the days of php 5 are over, I'd like to change this. Our method signature would then look like this.

publicfunction setToken(?TokenInterface$token);

We can do this for interfaces and abstract methods because an implementation may add a default value. Thus, removing the default value from the interface alone is not a BC break.

For the implementations of that interface, this is a different story because removing the default breaks calling code that omits the parameter entirely. This is why for the implementations I trigger a deprecation if the method is called without arguments. This enables us to remove the default in Symfony 6.

This PR performs the suggested changes forTokenStorageInterface andContainerAwareInterface, but we have a few more setters like this. But before I continue, I'd like to collect some feedback if this is something you would want to change.