不同类型的对象初始化

发布于 2024-10-19 23:39:49 字数 316 浏览 4 评论 0原文

你好之间是否有什么区别

MyClass calass = new MyClass()
{
  firstProperty = "text",
  secondProperty = "text"
}

我想知道这样的初始化对象和这样的初始化对象

MyClass calass = new MyClass   // no brackets
{
  firstProperty = "text",
  secondProperty = "text"
}

我也想知道这种初始化的名称是什么

原文

Hi
I was wondering if there is any difference between initializing object like this

MyClass calass = new MyClass()
{
  firstProperty = "text",
  secondProperty = "text"
}

and initializaing object like this

MyClass calass = new MyClass   // no brackets
{
  firstProperty = "text",
  secondProperty = "text"
}

I was also wondering what is the name of this kind of initialization

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街角迷惘 2024-10-26 23:39:49

不，绝对没有区别。在这两种情况下，您都使用对象初始值设定项表达式。对象初始值设定项是在 C# 3 中引入的。

在这两种情况下，这完全等同于：

// tmp is a hidden variable, effectively. You don't get to see it.
MyClass tmp = new MyClass(); 
tmp.firstProperty = "text";
tmp.secondProperty = "text";

// This is your "real" variable
MyClass calass = tmp;

请注意对 calass 的赋值仅在属性被赋值之后发生 - 就像您一样期望从源代码中得到。（在某些情况下，我相信 C# 编译器可以有效地删除额外的变量并重新排列分配，但它必须明显表现得像这个翻译。如果您重新分配现有的变量，它肯定会产生影响变量。）

编辑：关于省略构造函数参数的细微之处。如果这样做，它总是相当于包含一个空参数列表 - 但这与调用无参数构造函数不同。例如，可以有可选参数，或参数数组：

using System;
class Test
{
    int y;

    Test(int x = 0)
    {
        Console.WriteLine(x);
    }

    static void Main()
    {
        // This is still okay, even though there's no geniune parameterless
        // constructor
        Test t = new Test
        {
            y = 10
        };
    }
}

Nope, absolutely no difference. In both cases you're using an object initializer expression. Object initializers were introduced in C# 3.

In both cases, this is exactly equivalent to:

// tmp is a hidden variable, effectively. You don't get to see it.
MyClass tmp = new MyClass(); 
tmp.firstProperty = "text";
tmp.secondProperty = "text";

// This is your "real" variable
MyClass calass = tmp;

Note how the assignment to calass only happens after the properties have been assigned - just as you'd expect from the source code. (In some cases I believe the C# compiler can effectively remove the extra variable and rearrange the assignments, but it has to observably behave like this translation. It can certainly make a difference if you're reassigning an existing variable.)

EDIT: Slight subtle point about omitting constructor arguments. If you do so, it's always equivalent to including an empty argument list - but that's not the same as being equivalent to calling the parameterless constructor. For example, there can be optional parameters, or parameter arrays:

using System;
class Test
{
    int y;

    Test(int x = 0)
    {
        Console.WriteLine(x);
    }

    static void Main()
    {
        // This is still okay, even though there's no geniune parameterless
        // constructor
        Test t = new Test
        {
            y = 10
        };
    }
}

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