.delegate在groovy中意味着什麼？

Question

我發現這個代碼片段：

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

這apperantly打印2.它是如何工作的？哪裏可以找到有關.delegate的文檔？ Google讓我進入了代表轉換頁面，根本沒有提到.delegate。

Answer 1

閉包的委託是一個對象，用於解析在閉包本身內部無法解析的引用。如果您的例子是這樣寫的，而不是：

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

它打印「你好」，因爲m可以封閉內解決。然而，當m封閉內沒有被定義，

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

的delegate用於解析的引用，並且在這種情況下，delegate是Map映射封閉件的m至2

Answer 2

三個屬性是此，所有者和委派，通常代表被設置爲所有者

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 
    } 
} 

打印

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