关键字
Class－－创建一个类（object class）
instproc－－定义类的成员函数
instvar－－定义类的成员变量，首先检查变量在此类和父类中已声明（declare），是则引用（reference），否则声明
－superclass－－类继承，父类
$self——相当于C＋＋中的this指针
new－－创建一个类对象（object instance）
示例：
# add a member function call "great"
Class mom
mom instproc greet {} {
$self instvar age_
puts "$age_ year old mom say:
How are you doing?"
}
# Create a child class of "mom" called "kid"
#and overide the member function "greet"
Class kid -superclass mom
kid instproc greet {} {
$self instvar age_
puts "$age_ year old kid say:
What's up, dude?"
}
#Create a mom and a kid object, set each age
set a [new mom]
$a set age_ 45
set b [new kid]
$b set age_ 15
#Calling member function "greet" of each object
$a greet
$b greet
#end
（参考ns by example ex-otcl.tcl）
