Groovy中Closure的this到底指向谁？

Groovy in Action(中文版)第136页明确说Closure的this指向Closure自己。并且从代码注释处作者也是这样理解的：

class Mother{
    int field = 1
    int foo(){
        return 2
    }

    Closure birth(param){
        def local = 3
        def closure = { caller->
            [
                this,
                field,
                foo(),
                local,
                param,
                caller,
                this.owner
            ]
        }
        return closure
    }
}

Mother julia  = new Mother()

closure = julia.birth(4)
context = closure.call(this)
println context[0].class.name            //(4) Script

............................................

assert context[6] instanceof Mother //作者认为this指向自己，所以this.owner指向Mother

但是，上面的代码实际是错误的，我用1.0和2.1分别运行，都是一样的结果。this，也就是context[0]是Mother的this,而不是Closeure的。并且this.owner报错，提示Mother找不到属性owner.

其实Closure中引用this是它所在的上下文的this.对于上例其实就是Mother.this，是closure的owner,这也是Closure的delegate的默认值.要想在Closure是引用自己，只有引用delegate,然后在外部调用时将closure的delegate指向自己：

class Mother{
    int field = 1
    int foo(){
        return 2
    }

    Closure birth(param){
        def local = 3
        def closure = { caller->
            [
                delegate,
                field,
                this.foo(),
                local,
                param,
                caller,
                delegate.owner
            ]
        }
        return closure
    }
}

Mother julia  = new Mother()

closure = julia.birth(4)
closure.delegate = closure
context = closure.call(this)
println context[0].class.name