Groovy闭包委托定义参数？答案

【问题标题】：Groovy closure delegate define parameter?Groovy闭包委托定义参数？
【发布时间】：2017-05-04 16:21:54
【问题描述】：

我正在学习 groovy 委托

class GroovyGreeter {
    String greeting = "Default greeting"
    def printGreeting(){println "Greeting: $greeting"}
}
def myGroovyGreeter = new GroovyGreeter()
myGroovyGreeter.printGreeting() // default 
myGroovyGreeter.greeting = "My custom outer greeting"
myGroovyGreeter.printGreeting()
def greetingClosure = {
    println greeting  //equal to delegate.greeting
    println this.class
    println owner.class
    println delegate.class
    greeting = "Setting the greeting from a closure" // this is ??????
    printGreeting()
    delegate.greeting = "setting the greeting from delegate.greeting..."
    printGreeting()
}
greetingClosure.delegate = myGroovyGreeter
greetingClosure() // This works as `greeting` is a property of the delegate

操作系统：windows10 终端：cywin groovy:2.4.10 jvm 1.8

Greeting: Default greeting
Greeting: My custom outer greeting
My custom outer greeting
class closureuda
class closureuda
class GroovyGreeter
Greeting: My custom outer greeting
Greeting: setting the greeting from delegate.greeting...

我很困惑为什么闭包中的 greeting 变量不等于 delegate.greeting

当我反编译代码发现——greeting被定义为一个局部变量：

private static /* synthetic */ CallSiteArray $createCallSiteArray() {
    String[] strArr = new String[1]; // this  is greeting definition
    strArr[0] = "printGreeting";
    return new CallSiteArray(closureuda$_run_closure1.class, strArr);
}

【问题讨论】：

标签： groovy closures

【解决方案1】：

默认情况下，Groovy 会在访问委托之前查看闭包的作用域，因此要在委托中设置您想要的内容，这可能不是您想要的...幸运的是，您可以更改解析策略：

greetingClosure.resolveStrategy = Closure.DELEGATE_FIRST

将其放在该行之后

greetingClosure.delegate = myGroovyGreeter

你应该得到你期望的输出

【讨论】：