.delegate在groovy中意味着什么？

Question

我找到了这段代码:

def say = {println m}
say.delegate = [m:2]
say()

这显然是打印2.它是如何工作的？哪里可以找到有关的文档.delegate？谷歌引导我进入了代表转换页面,完全没有提到.delegate.

Answer 1

闭包的委托是一个对象,用于解析在闭包本身内部无法解析的引用.如果您的示例是这样写的:

def say = {
  def m = 'hello'
  println m
}
say.delegate = [m:2]
say()

它打印'hello',因为m可以在闭包内解决.但是,如果m没有在闭包内定义,

def say = {
  println m
}
say.delegate = [m:2]
say()

将delegate用于解析所述引用,并且在这种情况下delegate是一个Map映射m到2.

Answer 2

闭包的三个属性,是这个,所有者和委托,一般委托设置为所有者

def testClosure(closure) {
  closure()
}
testClosure() {
  println "this is " + this + ", super:" + this.getClass().superclass.name
  println "owner is " + owner + ", super:" + owner.getClass().superclass.name
  println "delegate is " + delegate + ", super:" + delegate.getClass().superclass.name

  testClosure() {
    println "this is " + this + ", super:" + this.getClass().superclass.name
    println "owner is " + owner + ", super:" + owner.getClass().superclass.name
    println "delegate is " + delegate + ", super:" + delegate.getClass().superclass.name
  }
}

版画

this is ConsoleScript0@11d20d3, super:groovy.lang.Script
owner is ConsoleScript0@11d20d3, super:groovy.lang.Script
delegate is ConsoleScript0@11d20d3, super:groovy.lang.Script
this is ConsoleScript0@11d20d3, super:groovy.lang.Script
owner is ConsoleScript0$_run_closure1@caea19, super:groovy.lang.Closure
delegate is ConsoleScript0$_run_closure1@caea19, super:groovy.lang.Closure