Marshal:最对象进行字节转换，并将字节反向转化为对象，应用在深层拷贝中，其中clone和dup只能做浅层拷贝，而marshal可以做深层拷贝。

#转换为了字节,dump
var = "demo"
str = Marshal.dump(var)

#字节转化为对象，load和restore
var = "demo"
str = Marshal.dump(var)
Marshal.load #"demo"
Marshal.restore #"demo"

应用：用Marshal实现深拷贝，即是对于对象的任何一层数组都进行了拷贝，即每一层数据都是指向不同的内存地址

a=["x", ["y", "z"]]
b=Marshal.load(Marshal.dump(a))

a[1][0]="t"
a #=>["x", ["t", "z"]]
#因为进行了深拷贝，a的二层数组值改变之后b并没有改变
b #=>["x", ["y", "z"]]

不能使用Marshal的对象

1.anonymous Class/Module.
2.objects which are related to system (ex: Dir, File::Stat, IO, File, Socket and so on)
3.an instance of MatchData, Data, Method, UnboundMethod, Proc, Thread, ThreadGroup, Continuation
4.objects which define singleton methods