contract Base {
    function foo() external returns (uint) {
        return 1234;
    }
    function bar() internal returns (uint) {
        return 1234;
    }
    function baz() public returns (uint) {
        return 1234;
    }
}

contract A is Base {
    function test() public returns (uint, uint, uint) {
        // solidity 0.4 allows this
        // uint a = foo();
        // with solidity 0.5 you have to explicitely use 'this.'
        uint a = this.foo();   // external use call
        uint b = bar();        // do not use call
        uint c = baz();        // do not use call
        return (a, b, c);
    }
}