标签：style blog io os ar for strong sp div
如果你不希望一个类被继承，那么可以把这个类声明为sealed类。
除此之外，声明为sealed类还会带来如下好处
1. 提高函数调用效率
JIT（Just in Time）编译器会优化sealed类的函数调用。
比如，如果从一个sealed class的实例上调用一个virtual method，那么就会把这次调用变成是non-virtual.
2. 更好的type safe保证
interface IInterface
{
}
class MyClass
{
}
class Program
{
static void Main(string[] args)
{
MyClass instance = new MyClass();
IInterface impl = (IInterface)instance;
}
}
上面的代码并不会编译出错，虽然MyClass并没有实现IInterface接口。这是因为，instance可能是MyClass的某个子类，而该子类实现了IInterface接口。
如果我们把MyClass声明为Sealed类
interface IInterface
{
}
sealed class MyClass
{
}
class Program
{
static void Main(string[] args)
{
MyClass instance = new MyClass();
IInterface impl = (IInterface)instance;
}
}
就会出现编译错误。
CLR via C#有一段关于sealed类的观点
When defining a new type, compilers should make the class sealed by default so that the class cannot be used as a base class. Instead, many compilers, including C#, default to unsealed classes and allow the programmer to explicitly mark aclass as sealed by using the sealed keyword. Obviously, it is too late now, but I think that today’s compilers have chosen the wrong default and it would be nice if it could change with future compilers. There are three reasons why a sealed class is better than an unsealed class:
- Versioning: When a class is originally sealed, it can change to unsealed in the future without breaking compatibility. (…)
- Performance: (…) if the JIT compiler sees a
call to a virtual method using a sealed types, the JIT compiler can
produce more efficient code by calling the method non-virtually.(…)
- Security and Predictability:
A class must protect its own state and not allow itself to ever become
corrupted. When a class is unsealed, a derived class can access and
manipulate the base class’s state if any data fields or methods that
internally manipulate fields are accessible and not private.(…)
标签：style blog io os ar for strong sp div
原文地址：http://www.cnblogs.com/wangguangxin/p/4011969.html
