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 = closurecontext = closure.call(this)println context[0].class.name