我已经为所有这些 lambdas 和很酷的 System::Linq 命名空间(包括 CLinq 库和其他东西)苦苦挣扎了几个小时,然后......我只是想:为什么不使用纯粹的静态决策?
我们只是声明
/// Convert X to "X", the classical preprocessing trick
#define GetPropName(TheClassName, ThePropertyName) #ThePropertyName
然后我们可以做
Console::WriteLine( GetPropName(TimeZone, Id) );
将“Id”打印在屏幕上。
是的……现在是有趣的部分。类型安全。我听到关于这个解决方案的评论风暴(“不!这不好,它不检查 ThePropertyName 是否在课堂上!”)
好的。解决方案:让我们使用在虚拟 TheClassName 实例中使用 ThePropertyName 的宏生成一些无意义的代码。
/// This macro will produce the compilation error if ThePropertyName is not in the class named TheClassName
#define CheckForPropertyExistence(TheClassName, ThePropertyName) \
/* Create an array of Objects which will be converted to string and ignored*/ \
(gcnew array<System::Object^> { (gcnew TheClassName())->ThePropertyName })->ToString()
/// We get the property name using the "dinosaur strategy" - good old macro concatenated with the empty string which in turn is formed in CheckFor() macro
#define GetPropertyName(TheClassName, ThePropertyName) \
(gcnew System::String(#ThePropertyName)) + CheckForPropertyExistence(TheClassName, ThePropertyName)->Substring(0,0)
现在我们可以给出完整的示例:
using namespace System;
/// Sample class
public ref class TheTimeZone
{
public:
TheTimeZone()
{
_Id = 0;
_DisplayName = "tmp";
}
property int Id
{
public:
int get() {return _Id;}
void set(int v) { _Id = v; }
}
property String^ DisplayName
{
public:
String^ get() { return _DisplayName; }
void set(String^ v) { _DisplayName = v; }
}
private:
int _Id;
String^ _DisplayName;
};
/// This macro will produce the error if ThePropertyName is not in the class named TheClassName
#define CheckForPropertyExistence(TheClassName, ThePropertyName) \
/* Create an array of Objects which will be converted to string and ignored*/ \
(gcnew array<System::Object^> { (gcnew TheClassName())->ThePropertyName })->ToString()
/// We get the property name using the "dinosaur strategy":
/// good old macro concatenated with the empty string
/// which in turn is formed in CheckFor() macro
#define GetPropertyName(TheClassName, ThePropertyName) \
(gcnew System::String(#ThePropertyName)) + \
CheckForPropertyExistence(TheClassName, ThePropertyName)->Substring(0,0)
/// To get properties from objects with no default constructor
#define GetPropertyNameForObject(TheObject, ThePropertyName) \
(gcnew System::String(#ThePropertyName)) + \
(gcnew array<System::Object^> { (TheObject)-> ThePropertyName })->ToString()->Substring(0,0)
/// Test for our macros
int main(array<System::String ^> ^args)
{
/// Prints "Length"
/// We cannot use default constructor here
Console::WriteLine(GetPropertyNameForObject (gcnew System::String("test"), Length) );
/// Prints "Id"
Console::WriteLine(GetPropertyName (TheTimeZone, Id) );
/// Uncomment and get the error
//Console::WriteLine(GetPropertyName (TheTimeZone, Id23) );
return 0;
}