http://www.yoda.arachsys.com/csharp/parameters.html
it is highly confusing to say that objects are passed by reference by default instead of the correct statement that object references are passed by value by default.
默认是值传递方式的参数传递,也就是没有addr指令来访问的。虽然可以改变同一份指向的东西,但是毕竟是有个新的引用变量。