带静态字段的switch语句 [英] Switch statement with static fields

问题描述

假设我有一堆静态字段，并且想在开关中使用它们：

Suppose I have a bunch of static fields and I want to use them in switch:

public static string PID_1 = "12";
public static string PID_2 = "13";
public static string PID_3 = "14";

switch(pid)
{
    case PID_1:
        //Do something 1
        break;
    case PID_2:
        //Do something 2
        break;
    case PID_3:
        //Do something 3
        break;
    default:
        //Do something default
        break;
}

由于C＃不允许在switch中使用非const语句。我想了解这种设计的意图。

Since C# doesn't allow non-const statement inside switch. I want to understand what is the intention of this kind of design. How should I do something like above in c#?

推荐答案

这些字符串值应该只是常量。

It looks like those string values should simply be constant.

public const string PID_1 = "12";
public const string PID_2 = "13";
public const string PID_3 = "14";

如果这不是一个选择（它们实际上在运行时已更改），则可以将该解决方案重构为一系列if / else if语句。

If that's not an option (they are actually changed at runtime), then you can refactor that solution into a series of if/else if statements.

为什么case语句需要保持不变；通过使它们恒定，可以使语句的优化程度更高。它实际上比一系列的if / else if语句更有效（尽管效果不是很明显，所以如果您没有很多条条件检查需要很长时间）。它将生成与case语句值作为键的哈希表等效的表。如果值可以更改，则无法使用该方法。

As to why the case statements need to be constant; by having them be constant it allows the statement to be much more heavily optimized. It is actually more efficient than a series of if/else if statements (although not dramatically so if you don't have lots of conditional checks that take a long time). It will generate the equivalent of a hash table with the case statement values as keys. That approach couldn't be used if the values can change.

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