Design of simple Crest objects

Before we start designing the Crest, let's take a look at the code.

Using System;

Using System. Collections. Generic;

 

Public abstract class Bird {

Protected String name;

Public abstract String tweet ();

Public String getName () {return name ;}

}

 

Public class Cock: Bird {

Public override String tweet () {return "woooooo ";}

Public virtual String walk () {return "cock walk ";}

Public void setName (String newName) {name = newName ;}

}

 

 

Public class MainClass

{

Public static void Main ()

{

Bird bird = new Cock ();

Cock cock = new Cock ();

System. Console. WriteLine (bird. tweet ());

}

}

This is a piece of pure object-oriented code, and our topic will follow this piece of code. First, we design Crest to support the simplest objects.

Simple Object

Because of the limitations of C language, we need to simulate a class definition that can only use struct. The simplest class is of course an empty class. Our C code is as follows:

Struct CEmptyObject

{

}

Then we need to add our CEmptyObject class to the member variable, which is also very simple:

Struct CEmptyObject

{

Int salary;

};

Add another member function. I want to add a getSalary, but the question is, how can I add it? Write the following statement:

Int getSalary () {return salary ;}

It seems correct, but the C compiler report salary cannot find it. If you put this line of code in struct CEmptyObject, it is also a compilation Error [BCC32 Error] raw. c (143): E2200 Functions may not be part of a struct or union. In fact, the implementation of most OO languages is similar, so we will not sell off the customs. We will copy them as follows:

Int getSalary (struct CEmptyObject * _ this)

{

Return _ this-> salary;

}

All code similar to xxx. getSalary () written in our code is actually converted into the getSalary (xxx) form. If you are familiar with the C # Extension function, you can better understand this.

Use of Simple objects

We have designed a simple object. Of course we need to use it. Let's take a look at it first.