CA2104警告：有什么方法可以将某个类标记为“不可变”以禁止它？ [英] The CA2104 warning: Is there any way to mark a class as `Immutable` to suppress it?

问题描述

请考虑以下代码，该代码会引发 CA2104：请勿声明只读可变引用类型。

 公共类Test 
 {
 // //引起CA2104：不要声明只读可变引用类型。 
受保护的只读ImmutableClass ImmutableMember; 
} 
 
公共类ImmutableClass 
 {
} 
  

有人知道不会以警告CA2104的方式将类标记为不可变吗？

我尝试装饰 > [ImmutableObject（true）] ，但没有成功的希望（因为该属性很明显可供表单编辑器使用），并且肯定它不起作用。

我假设代码分析在确定是否发出CA2104时使用的是已知的不可变类型的列表，因此我们不能使用相同的方法。

我想即使您可以将一个类标记为不可变，编译器也无法实际检查它是否为真，但至少可以

无论如何，我有没有忽略任何属性？

目前看来，没有其他方法可以执行此操作。

我确实找到了一个乔·达菲（ Windows上并行编程的作者）的一个有趣的博客，关于这种事情。

他从开始有一个ImmutableAttribute。 ...：）

这很有趣-他费心编写一些新的FxCop规则来进行类型分析

解决方案

受保护的只读字段不是真正的很清楚。由于受保护的，您可能希望派生类可以初始化该字段：

 公共类测试
 {
受保护的只读ImmutableClass ImmutableMember; 
} 
 
公共类SpecialTest：测试
 {
 public SpecialTest（）{ImmutableMember = new ImmutableClass; } 
} 
  

但是，事实并非如此，您会得到编译错误（CS0191）。 / p>

我不知道CA2104的确切推动力，但是您可以通过以下方式获得相同的结果而无需只读：

  public class Test 
 {
 protected ImmutableClass ImmutableMember {get;私有集；} 
 
 public Test（）
：this（new ImmutableClasse（））
 {
} 
 
 public Test（ImmutableClass immutableClass）
 {
 ImmutableMember = new ImmutableClasse（）; 
} 
} 
  

，并避免使用CA2104。

更新：

wrt就像您说的那样（对于将来的读者），您可以使用后备字段获取只读并提供受保护的getter来在派生类中获取它：

 公共类Test 
 {
 private readonly ImmutableClass immutableMember; 
 
受保护的ImmutableClass ImmutableMember {获取{return immutableMember; }} 
 
公共测试（ImmutableClass immutableMember）
 {
 this.immutableMember = immutableMember; 
} 
} 
  

Consider the following code, which provokes CA2104: Do not declare read only mutable reference types.

public class Test
{
    // This provokes CA2104: "Do not declare read only mutable reference types".
    protected readonly ImmutableClass ImmutableMember;
}

public class ImmutableClass
{
}

Does anyone know of a way to mark a class as immutable in a way that would suppress warning CA2104?

I tried decorating MutableClass with [ImmutableObject(true)] with no hope of success (since that attribute is pretty clearly for the Form Editor to use), and sure enough it doesn't work.

I assume that Code Analysis is using a list of known immutable types when determining whether to emit CA2104, so we can't use the same approach.

I guess that even if you could mark a class as immutable, there'd be no way for the compiler to actually check if it was true, but at least it could be a useful indicator.

Anyway, are there any attributes I'm overlooking? If not, suppression will have to do.

It seems that there is no alternative way to do this at the moment.

I did find an interesting blog from Joe Duffy (author of "Concurrent Programming On Windows") about this kind of thing.

He starts off with "Imagine we had an ImmutableAttribute."... :)

It's quite interesting - he went to the trouble of writing some new FxCop rules to do some analysis of types attributed as immutable.

解决方案

A protected readonly field isn't really that clear. As protected, you might expect that a derived class can initialize the field:

public class Test
{
    protected readonly ImmutableClass ImmutableMember;
}

public class SpecialTest : Test
{
    public SpecialTest() { ImmutableMember = new ImmutableClass; }
}

But, that's not the case--you will get a compile error (CS0191).

I don't know the exact impetus behind CA2104, but you can get the same result without readonly via:

public class Test
{
    protected ImmutableClass ImmutableMember {get; private set;}

    public Test()
        :this(new ImmutableClasse())
    {
    }

    public Test(ImmutableClass immutableClass)
    {
        ImmutableMember = new ImmutableClasse();
    }
}

and avoid the CA2104.

Update:

w.r.t. to the comments (and to future readers), as you say you could use a backing field to get the read-only and provide a protected getter to get at it in derived classes:

public class Test
{
    private readonly ImmutableClass immutableMember;

    protected ImmutableClass ImmutableMember { get { return immutableMember; } }

    public Test(ImmutableClass immutableMember)
    {
        this.immutableMember = immutableMember;
    }
}

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