Get variable dynamically

Question

Is there any way to reference variables dynamically like methods? Here is the Groovy example of referencing a method dynamically:

class Dog {
  def bark() { println "woof!" }
  def sit() { println "(sitting)" }
  def jump() { println "boing!" }
}

def doAction( animal, action ) {
  animal."$action"()                  //action name is passed at invocation
}

def rex = new Dog()

doAction( rex, "bark" )               //prints 'woof!'
doAction( rex, "jump" )               //prints 'boing!'

... But doing something like this doesn't work:

class Cat {
    def cat__PurrSound__List = ['a', 'b', 'c']
    def cat__MeowSound__List = [1, 2, 3]

    def someMethod(def sound) {
        assert sound == "PurrSound"

        def catSoundListStr = "cat__${obj.domainClass.name}__List"
        assert catSoundListStr = "cat__PurrSound__List"

        def catSoundList = "$catSoundListStr"
        assert catSoundList == cat__PurrSound__List // fail
    }
}

assert foo."$someMethod"() == "asdf" won't work, as you don't have a var called someMethod — tim_yates
– tim_yates, Commented Sep 3, 2013 at 14:20
@tim_yates Seems to work fine in my Grails test. I used it like the example here that uses $action. — ubiquibacon
– ubiquibacon, Commented Sep 3, 2013 at 15:15
@dmahapatro Sorry, I botched the question. As tim_yates said it doesn't work as advertised. I will corrected it. To be clear all I wanted to do was access a variable in a service based on a string that equaled that variables name. — ubiquibacon
– ubiquibacon, Commented Sep 3, 2013 at 16:00

tim_yates · Accepted Answer · 2013-09-03 15:28:45Z

3

Yeah, so you can do:

def methodName = 'someMethod'
assert foo."$methodName"() == "asdf" // This works

and to get the object by name, you can do (in a Script at least):

// Cannot use `def` in a groovy-script when trying to do this
foo  = new Foo()

def objectName = 'foo'
assert this."$objectName".someMethod() == "asdf"

edited Sep 3, 2013 at 15:28

answered Sep 3, 2013 at 14:19

tim_yates

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6 Comments

ubiquibacon Over a year ago

Awesome. Works in Grails too.

tim_yates Over a year ago

@dmahapatro What are you running it in? It very much depends on the context, as to whether the object will be found in this

dmahapatro Over a year ago

Same way OP has asked. This time I saved the script say BarScript.groovy. Here

tim_yates Over a year ago

@dmahapatro Oh yeah, because this is a Script, you have to remove the def from def foo = new Foo() to get it to work in a Script. Sorry about that...

dmahapatro Over a year ago

Correct, its tricky, negligence prone (for me at least). But I still do not understand the rationale behind using "$foo" instead of using foo directly. Asked OP about it. :)

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