Tcl8.6原生支持oop了

虽然tcl早先的版本就已经有oop的支持（itcl、XOTcl等），但是都是以外部扩展库的模式出现。因为习惯使用稳定版本，所以一直用tcl 8.5。前段时间安装了Mandriva 2010 sprint默认安装了tcl 8.6，于是下了相关文档浏览一下，发现Tcl Commands里面多了oo::class, oo::copy, oo::define, oo::objdefine, oo::object几条命令。由于时间比较晚，粗略看了下相关描述，让我比较惊奇的是tcl 8.6貌似同时支持两种类模型：基于类和基于原型，分别对应oo::class与oo::object，oo::class是经典的类模型，先上一段代码：

oo::class create fruit {
    method eat {} {
        puts "yummy!"
    }
}
oo::class create banana {
    superclass fruit
    constructor {} {
        my variable peeled
        set peeled 0
    }
    method peel {} {
        my variable peeled
        set peeled 1
        puts "skin now off"
    }
    method edible? {} {
        my variable peeled
        return $peeled
    }
    method eat {} {
        if {![my edible?]} {
            my peel
        }
        next
    }
}
set b [banana new]
$b eat               → prints "skin now off" and "yummy!"

上面的代码可以很直观看出oo::class是经典的基类继承模型，而oo::object则是：

set obj [oo::object new]
$obj foo             → error "unknown method foo"
oo::objdefine $obj method foo {} {
    my variable count
    puts "bar[incr count]"
}
$obj foo             → prints "bar1"
$obj foo             → prints "bar2"

这则代码中的方法是在对象创建后才动态添加的，很明显oo::object所创建出来的是metaclass，oo::class的描述也印证了我这个想法：

The oo::class class is the class of all classes; every class is aninstance of this class, which is consequently an instance of itself. Thisclass is a subclass of oo::object, so every class is also an object.Additional metaclasses (i.e. classes of classes) can be defined if necessaryby subclassing oo::class. Note that the oo::class object hides thenew method on itself, so new classes should always be made using thecreate method.

Thisclass is a subclass of oo::object, so every class is also an object.Additional metaclasses 很清楚地说明了任何用oo::class创建的类都是oo::object的子类，因此oo::classs实际就是oo::object的一种上层封装(基于原型的类模型比经典类模型具有更大自由度及灵活性)，由此大体可以看出tcl 8.6的原生类模型是一种基于原型的类模型。

时间较晚，研究得比较粗浅，大家就先凑合着看看当是开胃小菜吧....