Skip to content

Object-oriented programming

本文主要基于维基百科[Object-oriented programming。如果有一定的编程经验的话，可以较好理解，如果没有OOP的经验，可以阅读Java\book-Thinking-in-java，其中对OOP理论有非常好的描述。OOP有如下流派：

流派 example
Class-based programming 典型代表有C++、Java、Python
Prototype-based programming 典型代表就是 JavaScript

wikipedia Object-oriented programming

Object-oriented programming (OOP) is a programming paradigm based on the concept of "objects", which can contain data, in the form of fields (often known as attributes or properties), and code, in the form of procedures (often known as methods). A feature of objects is an object's procedures that can access and often modify the data fields of the object with which they are associated (objects have a notion of "this" or "self"). In OOP, computer programs are designed by making them out of objects that interact with one another.

Features

NOTE: 原文的本段说明非常多我们平时所听到的与OOP相关的概念。我将与class-base OOP相关的内容放到了Class-based OOP中。

Shared with non-OOP predecessor languages

Objects and classes

NOTE: 在Class-based OOP中会对此进行介绍。

Class-based vs prototype-based

Dynamic dispatch/message passing

NOTE: 这是OOP中非常主要的一个概念

It is the responsibility of the object, not any external code, to select the procedural code to execute in response to a method call, typically by looking up the method at run time in a table associated with the object. This feature is known as dynamic dispatch, and distinguishes an object from an abstract data type (or module), which has a fixed (static) implementation of the operations for all instances. If the call variability（可变性） relies on more than the single type of the object on which it is called (i.e. at least one other parameter object is involved in the method choice), one speaks of multiple dispatch.

A method call is also known as message passing. It is conceptualized as a message (the name of the method and its input parameters) being passed to the object for dispatch.

Encapsulation

Composition, inheritance, and delegation

NOTE: 在Theory\Programming-paradigm\Object-oriented-programming\Assemble章节，对这部分内容进行了专门的介绍。

Objects can contain other objects in their instance variables; this is known as object composition. For example, an object in the Employee class might contain (either directly or through a pointer) an object in the Address class, in addition to its own instance variables like "first_name" and "position". Object composition is used to represent "has-a" relationships.

Languages that support classes almost always support inheritance. This allows classes to be arranged in a hierarchy that represents "is-a-type-of" relationships.

Subclasses can override the methods defined by superclasses.

Delegation is another language feature that can be used as an alternative to inheritance.

Polymorphism

NOTE: 在Theory\Programming-paradigm\Object-oriented-programming\Polymorphism章节将对它进行详细说明。

Open recursion

OOP languages

NOTE: 我们常常会听到“纯面向对象”、“部分支持明细对象”等说法，原文的这一段对此进行了说明。

Concerning the degree of object orientation, the following distinctions can be made:

  • Languages called "pure" OO languages, because everything in them is treated consistently as an object, from primitives such as characters and punctuation, all the way up to whole classes, prototypes, blocks, modules, etc. They were designed specifically to facilitate, even enforce, OO methods. Examples: Python
  • Languages designed mainly for OO programming, but with some procedural elements. Examples: Java, C++

Class-based vs prototype-based

关于Class-based vs prototype-based，在维基百科Object-oriented programming的Class-based vs prototype-based段中有总结。下面是我根据自己的一些经验所总结的：

从type system的角度来进行对比

OOP的class-based流派，每个**class**对应一种**类型**，往往是**强类型**语言使用，比如c++，Java等。

OOP的prototype-based流派，并没有class的概念，往往是weak类型语言使用，比如JavaScript。

Behavior and data member

后续为了描述的统一性，使用**behavior**来表示method、function member，使用data member来表示“成员变量”；

在Theory\Programming-paradigm\Object-oriented-programming\Behaivor.md中对behavior进行了总结。

OOP and “function and data model”

在工程hardware的Computer-architecture\Stored-program-computer.md中，我们介绍了Function and data model。OOP的object是符合“function and data model”的，下面描述了它们的对应关系:

OOP的object function and data model
function member function
data member data

关于C++ OOP and “function and data model”，参见C-family-language\C++\Language-reference\Basic-concept\index.md。