groovy中.delegate意味着什么？

问题描述

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

哪里可以找到有关 .delegate 的文档？ Google让我进入了Delegate Transformation页面，该页面根本没有提及 .delegate 。

解决方案

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。如果你的例子是这样写的：

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

它会打印'hello'，因为 m 可以在闭包中解析。然而，当 m 没有在闭包中定义时，

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

使用委托来解析引用，在这种情况下，委托是一个 Map ，它将 m 映射到2。

I found this code snippet:

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

That apperantly prints 2. How does it work? Where can find documentation about .delegate? Google led me to the Delegate Transformation page that doesn't mention .delegate at all.

解决方案

The delegate of a closure is an object that is used to resolve references that cannot be resolved within the body of the closure itself. If your example was written like this instead:

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

It prints 'hello', because m can be resolved within the closure. However, when m is not defined within the closure,

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

the delegate is used to resolve the reference, and in this case the delegate is a Map that maps m to 2.

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