Scala隐式参数的Groovy等价物 - 扩展

Question

This question extends my previous one Groovy equivalent for Scala implicit parameters

Not sure if this is the right way to develop from a previous topic, but anyway..

I am looking for a way to express in groovy something like this:

// scala
object A {
    def doSomethingWith(implicit i:Int) = println ("Got "+i)
}
implicit var x = 5

A.doSomethingWith(6)  // Got 6
A.doSomethingWith     // Got 5

x = 0
A.doSomethingWith     // Got 0

In general, I would like to execute a piece of logic, and have variables in it resolved based on the execution 'context'. With implicits in scala I seem to be able to control this scenario. I am trying to find a way to do something similar in groovy.

Based on the feedback from the first question I tried to approach it like this:

// groovy
class A {
    static Closure getDoSomethingWith() {return { i = value -> println "Got $i" }} 
}

value = 5

A.doSomethingWith(6)  // Got 6
A.doSomethingWith()   /* breaks with
                         Caught: groovy.lang.MissingPropertyException: 
                         No such property: value for class: A */

Now, I went through the groovy closure definition at http://groovy.codehaus.org/Closures+-+Formal+Definition

As I understand it, when the getter is called, the failure happens as "the compiler cannot statically determine that 'value' is available"

So, has anyone a suggestion for this scenario? Cheers

Answer 1

You could also try changing the delegate of the returned Closure:

value = 5

Closure clos = A.doSomethingWith

// Set the closure delegate
clos.delegate = [ value: value ]

clos(6)  // Got 6
clos()   // Got 5

Answer 2

I managed to do what you want by checking for unresolved properties in the script binding:

class A {
  static Closure getDoSomethingWith() { { i = value -> println "Got $i" } } 
}
A.metaClass.static.propertyMissing = { String prop -> binding[prop] }

value = 5


A.doSomethingWith 6  // Got 6
A.doSomethingWith() // prints "Got 5"