Groovy闭包

• 闭包定义与调用

    //默认参数 it
    Closure c = {
        it+5
    }

    //显式命名参数，此时就没有it
    Closure d = { k ->
        k+5
    }
    
    //闭包的调用
    c.call(7)

*动态闭包

    def f(Closure closure){
        //根据闭包的参数的个数执行不同的逻辑
        if (closure.maximumNumberOfParameters == 2){}
        else{}   
        
        for (param in closure.parameterTypes){
            param.name //参数的类型
        }
    }

    //不同参个数的闭包调用的内部逻辑是不一样的
    f{ param1 -> }
    f{ param1,param2 -> }

• this、owner、delegate
  闭包里面有3个重要的对象，把它们弄清楚了，才能对一些代码有全面的理解
  this:创建闭包的对象（上下文）
  owner：如果闭包在另外一个闭包中创建，owner指向另一个的闭包，否则指向this
  delegate：默认指向owner，但可以设置为其他对象

闭包里面的属性和方法调用与三个对象有密切的关系，闭包中有个resolveStrategy，默认值为0

    public static final int OWNER_FIRST = 0;
    public static final int DELEGATE_FIRST = 1;
    public static final int OWNER_ONLY = 2;
    public static final int DELEGATE_ONLY = 3;

属性或者方法调用的查找顺序
OWNER_FIRST:
own -> this -> delegate

DELEGATE_FIRST
delegate->own -> this

class Hello {

//    def a = "hello a"
    def innerC

    def c = {
//        def a = "closure a"

        innerC = {
            println(a)
        }

        delegate = new Delegate()

        //修改闭包的delegate
        innerC.delegate = delegate
        //设置闭包的代理策略
        innerC.setResolveStrategy(Closure.OWNER_FIRST)

        innerC.call()
    }

    def f(){
        c.call()
    }

}

class Delegate {
    def a = "delegate a"
}