Constructor Visibility

[Abubaker Bashir (AbubakerB)]

Constructor Visibility

(This is a updated PR from #4174)

There wasn't any detailed proposal, so I'm just going to list what this PR implements.

1) Constructor Visibility

1. A constructor can now have the private or protected keyword on its signature.
2. All constructor overloads must be of the same visibility (i.e. all private, protected, or public)

2) Private Constructors

A class with a private constructor:

1. Can only be instantiated within it's own class.
2. Can only be extended within it's own class.

3) Protected Constructors

A class with a protected constructor:

1. Can only be instantiated within it's own class.
2. Can be extended.

4) Signature Assignability

• A public, protected and private signature is assignable to a private signature.
• A public and protected signature is assignable to a protected signature.
• A public signature is assignable to public signature.