Switch/case语句中的String.Empty生成编译器错误

Question

如果String.Empty一样好"",那么编译器如何在语句中抛出string.Empty case呢？string.Empty在我看来,没有比这更稳定的了.谁知道？谢谢!

switch (filter)
            {
     case string.Empty:  // Compiler error "A constant value is expected"

                break;

                case "":  // It's Okay.
                    break;

            }

Answer 1

您可以尝试这样:

switch(filter ?? String.Empty)

string.Empty是只读字段,""而是编译时常量.您还可以在此处查看Code Project String.Empty Internals上的文章

//The Empty constant holds the empty string value.
//We need to call the String constructor so that the compiler doesn't
//mark this as a literal.
//Marking this as a literal would mean that it doesn't show up as a field 
//which we can access from native.

public static readonly String Empty = ""; 

在旁注:

当您在方法(C#4.0)中提供默认参数值时,您还会看到此问题:

void myMethod(string filter = string.Empty){}

以上将导致编译时错误,因为默认值需要是常量.