如何在C#中进行构造函数链接 [英] How to do constructor chaining in C#

问题描述

我知道这应该是一个非常简单的问题，但是一段时间以来我一直在为这个概念而苦苦挣扎.

I know that this is supposedly a super simple question, but I've been struggling with the concept for some time now.

我的问题是，如何在C#中链接构造函数?

My question is, how do you chain constructors in C#?

我正在上第一门OOP课程，所以我只是在学习.我不了解构造函数链接的工作方式或实现方式，甚至不为什么比不进行链接的构造函数更好.

I'm in my first OOP class, so I'm just learning. I don't understand how constructor chaining works or how to implement it or even why it's better than just doing constructors without chaining.

我将对一些带有解释的示例表示赞赏.

I would appreciate some examples with an explanation.

那么如何将它们链接起来?
我知道有两个:

So how do how chain them?
I know with two it goes:

public SomeClass this: {0}

public SomeClass
{
    someVariable = 0
} 

但是您怎么用三个，四个等等呢?

But how do you do it with three, four and so on?

同样，我知道这是一个初学者的问题，但是我很难理解这一点，我也不知道为什么.

Again, I know this is a beginner question, but I'm struggling to understand this and I don't know why.

推荐答案

您使用标准语法(将this用作方法)来选择重载，内部该类:

You use standard syntax (using this like a method) to pick the overload, inside the class:

class Foo 
{
    private int id;
    private string name;

    public Foo() : this(0, "") 
    {
    }

    public Foo(int id, string name) 
    {
        this.id = id;
        this.name = name;
    }

    public Foo(int id) : this(id, "") 
    {
    }

    public Foo(string name) : this(0, name) 
    {
    }
}

然后:

Foo a = new Foo(), b = new Foo(456,"def"), c = new Foo(123), d = new Foo("abc");

另请注意:

• 您可以使用base(...)
链接到基本类型的构造函数
• 您可以在每个构造函数中添加额外的代码
• 默认值(如果您未指定任何内容)为base()

• you can chain to constructors on the base-type using base(...)
• you can put extra code into each constructor
• the default (if you don't specify anything) is base()

对于为什么?":

• 减少代码(总是一件好事)

• 必要的来调用非默认的基本构造函数，例如:

• code reduction (always a good thing)

• necessary to call a non-default base-constructor, for example:

SomeBaseType(int id) : base(id) {...}

请注意，尽管(无需编写任何内容)，您也可以类似的方式使用对象初始化程序:

Note that you can also use object initializers in a similar way, though (without needing to write anything):

SomeType x = new SomeType(), y = new SomeType { Key = "abc" },
         z = new SomeType { DoB = DateTime.Today };

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