CODEWITHSUNDEEP
actionscript-3
Brian Genisio
Brian Genisio

Reputation: 48157

Re-defining named functions at runtime

What I am trying to do is kind of odd, but I am wondering if anyone can come up with a clever way to do what I want to do. Basically, I want to re-define a named function at runtime. I can do this with anonymous functions, but I can't figure out a way to do it for named functions. I want to do this so that I can implement a "spy" functionality on an object for a testing framework (a port of Jasmine to Flex).

Take, for instance, this class:

public class TestClass
{
    public var anonymous:Function = function():void { 
        trace("original anonymous"); 
    };

    public function named():void {
        trace("original named");
    }
}

I can easily re-define the anonymous function because it is just a variable. Javascript uses this idiom a lot. 

var testClass:TestClass = new TestClass();
testClass.anonymous = function():void { trace("overridden anonymous"); }

BUT, when I do the same thing for named functions, you get a compile-time error:

// Does not compile
testClass.named = function():void { trace("overridden named"); }

I tried to make it a bit more "squishy" but this leads to a runtime failure "Cannot assign to a method named on TestClass".

// Compiles with runtime failure
testClass["named"] = function():void { trace("overridden named"); }

Can anyone more clever than I come up with a way to hack this? Can the bytecode be hijacked? Something?

Upvotes: 3

Views: 1438

Answers (3)

alxx
alxx

Reputation: 9897

I want to modify an object, not a class

But object doesn't contain functions, only non-static variables. I tried to use prototype property and replace method there, but original method still gets called instead of injected one.

About "hack" bytecode, do you mean "hack" already loaded SWF in runtime? I think it's not possible. I'm sure, though, you can parse SWF with something like as3swf, find method in bytecode, replace it and save result in new SWF.

Upvotes: 1

Chunky Chunk
Chunky Chunk

Reputation: 17237

an easy way to accomplish what you want is to simply pass a new function to the original function and execute it from there:

package
{
//Imports
import flash.display.Sprite;

//Class
public class RedefineFunction extends Sprite
    {
    //Constructor
    public function RedefineFunction()
        {
        originalFunction();

        originalFunction(redefinedFunction);
        }

    //Original Function
    public function originalFunction(redefinition:Function = null):void
        {
        if  (redefinition != null)
            redefinition();
            else
            trace("Original Function Definition");
        }

    //Redefined Function
    private function redefinedFunction():void
        {
        trace("Redefined Function Definition")
        }
    }
}

traces:

Original Function Definition
Redefined Function Definition

Upvotes: 0

ruedaminute
ruedaminute

Reputation: 579

I had an idea bout making a function "cache" . This might work with what you need.

Let's say you have a class "Car" with a method you need to redefine at runtime:

public class Car extends Sprite
{
    private var functionCache:Function;

    public function Car()
    {
        super();
    }

    public function flexibleFunction(functionBody:*=null):void{
        if(functionBody is Function){
            functionBody.call();
            functionCache=functionBody;
        } else {
            functionCache(functionBody);
        }
    }
}

Usage:

public class Main extends Sprite
{
    private var car:Car;

    public function Main()
    {
        car = new Car();

        car.flexibleFunction(function(){trace("redefine test #1")});

        car.flexibleFunction();

        car.flexibleFunction(function(doParametersWork:String="let's see"){trace("redefine test #2: " + doParametersWork);});

        car.flexibleFunction("yes they do");

        car.flexibleFunction();

    }
}

Upvotes: 0

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