Method Calls another Method

**FourAngels** · 09-07-2015

Finished reading ch 9 of Programming Principals but I have a question. The part where a default constructor is defined for a class called Date. The constructor initialized three variables that are located in the private sphere of the Date object (year, month, and day). At any rate, these three variables since they are private members, their values are otherwise accessed through acessor methods. During default construction this same method containing a static default value, separately calls each one of these public acessor methods and the return type of this culprit in question is a Date object. The way that it is written in the default construction, this method calls each of the three acessor methods in turn so that all three Date elements are initialized. This looked highly unusual. Why can a method call another method?

Code:

Date::Date()
  :y{default_date().year()},
  :m{default_date().month(),
  :d{default_date().day()}
{
}

Also

Code:

const Date& default_date() {
  static Date dd {2001, Month::Jan, 1};
  return dd;
}

**laserlight** · 09-07-2015

Originally Posted by FourAngels

Why can a method call another method?

You are looking at an example, of chaining of function calls. A method (or more generally in C++ terminology: a member function) calling another method might look like this:

Code:

class X
{
public:
    void foo() {}

    void bar()
    {
        foo();
    }
};

That is, the member function bar calls the member function foo.

For the chaining of function calls, on the other hand, we see that default_date() in your example returns a const reference to a Date object, so the year, month and day member functions are called on that Date object.

You may have encountered or will encounter this when overloading operator<< and operator>> for I/O streams.

**FourAngels** · 09-07-2015

I can see how it works similar to :

Code:

Date Example {2010, Month::May, 11};
std::cout << Example.year() << std::end;
// default_date().year(); instead of Example.year()

Okay it was the first time I had ever seen chaining. He did not explain that. Thanks.

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