自动性质与结构不混合？ [英] Automatic Properties and Structures Don't Mix?

问题描述

周围的一些小的结构踢在回答这个帖子，我遇到意外以下几点：

下面的结构，使用一个int字段是完全合法的：

 结构MYSTRUCT 
 {
公共MYSTRUCT（INT大小）
 {
 this.Size =大小; //<  - 法律分配。 
} 
 
公众诠释大小; 
} 
  

但是，下面的结构，使用自动属性不会编译：

 结构MYSTRUCT 
 {
公共MYSTRUCT（INT大小）
 {
本。大小=; //<  - 编译时错误！ 
} 
 
公众诠释大小{搞定;集;} 
} 
  

返回的的这个对象不能使用的错误之前所有字段被分配到。我知道，这是一个结构的标准程序：对于任何属性支持字段必须直接从结构的构造内进行分配（而不是通过属性的set访问）。

一个解决方法是使用一个明确的支持领域：

 结构MYSTRUCT 
 {
公共MYSTRUCT（INT大小）
 {
 = _size大小; 
} 
 
私人诠释_size; 
 
公众诠释大小
 {
 {返回_size; } 
集合{_size =价值; } 
} 
} 
  

（请注意，VB.NET不会有这种的问题，因为在VB.NET各个领域都将自动初始化为0 /空/假时，第一个创建的。）

这似乎是使用自动属性时，是一个不幸的限制在C＃结构。从概念上思考，我想知道，这不会是一个合理的地方，那里是一个例外，它允许属性set访问到一个结构的构造函数中调用，至少在一个自动的财产？

这是一个小问题，几乎是一个边缘的情况下，但我不知道别人怎么想到这个问题...

解决方案

从C＃6起：这不再是一个问题。

---

Becore C＃6，您需要调用默认的构造函数这个工作：

 公共MYSTRUCT（INT大小）：这个（）
 {
尺寸=尺寸; 
} 
  

这里的一个更大的问题是，你有一个可变的结构。这就是绝不会一个好主意。我将使它：

 公众诠释大小{搞定;私人集;} 
  

不是的技术上的不可变的，但足够接近

Kicking around some small structures while answering this post, I came across the following unexpectedly:

The following structure, using an int field is perfectly legal:

struct MyStruct
{ 
    public MyStruct ( int size ) 
    { 
        this.Size = size; // <-- Legal assignment.
    } 

    public int Size; 
}

However, the following structure, using an automatic property does not compile:

struct MyStruct
{ 
    public MyStruct ( int size ) 
    { 
        this.Size = size; // <-- Compile-Time Error!
    } 

    public int Size{get; set;}
}

The error returned is "The 'this' object cannot be used before all of its fields are assigned to". I know that this is standard procedure for a struct: the backing field for any property must be assigned directly (and not via the property's set accessor) from within the struct's constructor.

A solution is to use an explicit backing field:

struct MyStruct
{ 
    public MyStruct(int size)
    {
        _size = size;
    }

    private int _size;

    public int Size
    {
        get { return _size; }
        set { _size = value; }
    }
}

(Note that VB.NET would not have this issue, because in VB.NET all fields are automatically initialized to 0/null/false when first created.)

This would seem to be an unfortunate limitation when using automatic properties with structs in C#. Thinking conceptually, I was wondering if this wouldn't be a reasonable place for there to be an exception that allows the property set accessor to be called within a struct's constructor, at least for an automatic property?

This is a minor issue, almost an edge-case, but I was wondering what others thought about this...

解决方案

From C# 6 onward: this is no longer a problem

---

Becore C# 6, you need to call the default constructor for this to work:

public MyStruct(int size) : this()
{
    Size = size;
}

A bigger problem here is that you have a mutable struct. This is never a good idea. I would make it:

public int Size {get; private set;}

Not technically immutable, but close enough.

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