常量不能标记静 [英] The constant cannot be marked static

问题描述

我想声明像这样的PI常数：

 公共静态常量双PI = Math.PI; 
  

但为什么我收到此错误？

 常量'Calendar.NewCalendar.PI'不能标记静态
  

解决方案

常量意味着静态（你不需要一个实例引用常量值）。

我也想加入这个重要的一点：当您使用公共常量连结反对（参考）组装 ，该值的复制到您的装配。因此，如果在引用的程序集的变化常量价值，你的程序集将仍然有原来编译的值。

如果这种行为的不的可以接受的，那么你应该考虑该领域的公共静态只读字段。

的 Lib.dll，二进制提供的：的

 公共类Foo {
酒店的公共const int的HATS = 42; 
公共静态只读INT手套= 33; 
} 
  

的 APP.EXE，引用Lib.dll：的

  Foo.HATS //这将永远是42即使Lib.dll变化，
值//除非APP.EXE重新编译。 
 
 Foo.GLOVES //这将始终是相同的如Lib.dll 
  

$ Foo.GLOVES b $ b

---

：

不要创建一个常数来表示你希望在任何时候更改信息。例如，不使用常数域，存储服务，产品版本号，或者一个公司的品牌名称的价格。这些值可随时间而改变，并且因为编译器传播常量，与库编译其他代码将不得不被重新编译以查看更改

通过 DotNetPerls ：

的DLL 。当您使用常量字段或声明，C＃编译器实际上嵌入常量变量的直接价值的IL代码。因此，它本质上擦除常量作为一个独立的实体。

注意：
如果依赖程序在常量未在常量后重新编译值发生变化，它们可能会破坏[，因为它们将继续使用前值的。

I am trying to declare a PI constant like this:

public static const double PI = Math.PI;

but why am I getting this error?

The constant 'Calendar.NewCalendar.PI' cannot be marked static

解决方案

const implies static (you don't need an instance to reference the const value).

I want to also add this important point: When you link against (reference) an assembly with a public const, that value is copied into your assembly. So if the const value in the referenced assembly changes, your assembly will still have the originally compiled-in value.

If this behavior is not acceptable, then you should consider making the field a public static readonly field.

Lib.dll, provided as binary:

public class Foo {
    public const int HATS = 42;
    public static readonly int GLOVES = 33;
}

App.exe, references Lib.dll:

Foo.HATS    // This will always be 42 even if the value in Lib.dll changes,
            // unless App.exe is recompiled.

Foo.GLOVES  // This will always be the same as Foo.GLOVES in Lib.dll

---

From MSDN:

Don’t create a constant to represent information that you expect to change at any time. For example, don’t use a constant field to store the price of a service, a product version number, or the brand name of a company. These values can change over time, and because compilers propagate constants, other code compiled with your libraries will have to be recompiled to see the changes.

From DotNetPerls:

DLLs. When you use a const field or declaration, the C# compiler actually embeds the const variable's value directly in the IL code. Therefore, it essentially erases the const as a separate entity.

Caution: If programs that depend on a const are not recompiled after the const value changes, they may break [because they'll continue to use the previous value].

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