.delegate在groovy中意味着什么？

Question

我找到了這段代碼：

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

這顯然是打印2.它是如何工作的？ 哪里可以找到關於.delegate文檔？ 谷歌引導我進入代表轉換頁面，完全沒有提到.delegate 。

Answer 1

閉包的委托是一個對象，用於解析在閉包本身內部無法解析的引用。 如果您的示例是這樣寫的：

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

它打印'hello'，因為m可以在閉包內解析。 但是，當m沒有在閉包內定義時，

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

delegate用於解析引用，在這種情況下， delegate是將m映射到2的Map 。

Answer 2

閉包的三個屬性，是這個，所有者和委托 ，一般委托設置為所有者

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
  }
}

版畫

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