Solidity - Visibility.

visibility.sol

pragma solidity ^0.4.17;

contract Base {
  event Called(string name);
  
  function public_fn() public { Called("Base.public_fn"); }
  function private_fn() private { Called("Base.private_fn"); }
  function external_fn() external { Called("Base.external_fn"); }
  function internal_fn() internal { Called("Base.internal_fn"); }
  function () public payable { Called("Base.fallback"); }
  
  function fn() public {
    // Function called internally.
    public_fn(); // Calls: Base.public_fn
    private_fn(); // Calls: Base.private_fn
    //external_fn(); // Error: Undeclared identifier.
    internal_fn(); // Calls: Base.internal_fn
    
    // Function called externally.
    this.public_fn(); // Calls: Base.public_fn
    //this.private_fn(); // Error: Member "private_fn" not found or not visible after argument-dependent lookup in contract Base
    this.external_fn(); // Calls: Base.external_fn
    //this.internal_fn(); // Error: Member "internal_fn" not found or not visible after argument-dependent lookup in contract Base

    // Function called on contract type.
    Base.public_fn(); // Calls: Base.public_fn
    //Base.private_fn(); // Error: Member "private_fn" not found or not visible after argument-dependent lookup in type(contract Base)
    //Base.external_fn(); // Error: Member "external_fn" not found or not visible after argument-dependent lookup in type(contract Base)
    Base.internal_fn(); // Calls: Base.internal_fn

    // Function called dynamically on raw address.
    address(this).call(bytes4(keccak256("public_fn()"))); // Calls: Base.public_fn
    address(this).call(bytes4(keccak256("private_fn()"))); // Calls: Base.fallback
    address(this).call(bytes4(keccak256("external_fn()"))); // Calls: Base.external_fn
    address(this).call(bytes4(keccak256("internal_fn()"))); // Calls: Base.fallback
  }
}

contract Derived is Base {
  event Called(string name);
  
  function public_fn() public { Called("Derived.public_fn"); }
  function private_fn() private { Called("Derived.private_fn"); }
  function external_fn() external { Called("Derived.external_fn"); }
  function internal_fn() internal { Called("Derived.internal_fn"); }
  function () public payable { Called("Derived.fallback"); }
  
  function fn() public {
    // Function called internally.
    public_fn(); // Calls: Derived.public_fn
    private_fn(); // Calls: Derived.private_fn
    //external_fn(); // Error: Undeclared identifier.
    internal_fn(); // Calls: Derived.internal_fn
    
    // Function called externally.
    this.public_fn(); // Calls: Derived.public_fn
    //this.private_fn(); // Error: Member "private_fn" not found or not visible after argument-dependent lookup in contract Derived
    this.external_fn(); // Calls: Derived.external_fn
    //this.internal_fn(); // Error: Member "internal_fn" not found or not visible after argument-dependent lookup in contract Derived

    // Function called on contract type.
    Derived.public_fn(); // Calls: Derived.public_fn
    //Derived.private_fn(); // Error: Member "private_fn" not found or not visible after argument-dependent lookup in type(contract Derived)
    //Derived.external_fn(); // Error: Member "external_fn" not found or not visible after argument-dependent lookup in type(contract Derived)
    Derived.internal_fn(); // Calls: Derived.internal_fn

    // Function called on parent contract type.
    Base.public_fn(); // Calls: Base.public_fn
    //Base.private_fn(); // Error: Member "private_fn" not found or not visible after argument-dependent lookup in type(contract Base)
    //Base.external_fn(); // Error: Member "external_fn" not found or not visible after argument-dependent lookup in type(contract Base)
    Base.internal_fn(); // Calls: Base.internal_fn

    // Function called dynamically on raw address.
    address(this).call(bytes4(keccak256("public_fn()"))); // Calls: Derived.public_fn
    address(this).call(bytes4(keccak256("private_fn()"))); // Calls: Derived.fallback
    address(this).call(bytes4(keccak256("external_fn()"))); // Calls: Derived.external_fn
    address(this).call(bytes4(keccak256("internal_fn()"))); // Calls: Derived.fallback
  }
}