Coldfusion代理混淆

Question

I am using a proxy/delegate pattern in a coldfusion component, and am getting unexpected results (from my point of view). Below is my proxy component - its pretty straight forward, I just init the CFC with the actual component I want to delegate to, and then map the named functions from that CFC through to a proxy function (the below is simplified for this example)

I have created a proxy component as follows:

component output="false"{

    /** Constructor for proxy - requires an instance of myFusebox **/
    public MyFuseboxProxy function init( Required any myFb ){
        variables.myFusebox = arguments.myFb;
        return this;
    }

    this.do = variables.proxy;
    this.getApplication = variables.proxy;
    this.getApplicationData = variables.proxy;

    private any function proxy(){    
        var local.functionName = getFunctionCalledName();
        var local.function = variables.myFusebox[local.functionName];
        var local.returnVal = local.function( argumentCollection=arguments );

        return local.returnVal;
    }
}

From my application I call the following code:

    variables.myFusebox = new ab.MyFuseboxProxy( variables.myFusebox );
    variables.myFusebox.getApplicationData().startTime = now();

Now, in the above scenario, I would expect my proxy component to map the getApplicationData() function straight through to the original myFusebox component (via my proxy() function).

That function in the underlying component is as follows:

<cffunction name="getApplicationData" returntype="struct" access="public" output="false"
            hint="I am a convenience method to return a reference to the application data cache.">
    <cfreturn getApplication().getApplicationData() />
</cffunction>

That proxy all works fine, however, once I am in the above function in the original myFusebox I get the following error:

Message: Variable GETAPPLICATION is undefined.
StackTrace: coldfusion.runtime.UndefinedVariableException: Variable GETAPPLICATION is undefined.

And if I dump " this " inside that function, it actually dumps my proxy object.

Can anyone explain this or what I have done wrong? I was expecting that once the function call was inside the underlying object, it would just use its own context from there (my proxy just being a pass through really to the delegate)

Answer 1

I think this is the key point:

I was expecting that once the function call was inside the underlying object

You've got this:

private any function proxy(){    
    var local.functionName = getFunctionCalledName();
    var local.function = variables.myFusebox[local.functionName];
    var local.returnVal = local.function( argumentCollection=arguments );

    return local.returnVal;
}

When you do this bit:

var local.function = variables.myFusebox[local.functionName];

you are effectively pulling the function referenced by local.functionName out of variables.myFusebox , and putting it into the current function, within the context of your MyFuseboxProxy instance.

So when you do this:

var local.returnVal = local.function( argumentCollection=arguments );

You are not running variables.myFusebox[local.functionName]() (so in the context of variables.myFusebox ), but you are running local.function() (so in the context of your proxy object).

I don't have the patience to try to follow your logic here, but I am still surprised you get that error. I would have expected this to happen:

1. local.function (a reference to getApplicationData from variables.myFusebox ) runs getApplication() .
2. getApplication() in the context of the MyFuseboxProxy instance should be a reference to variables.proxy() .
3. variables.proxy() resolves the proxied function as getApplication() , and pulls that out of variables.myFusebox , and runs it in the context of your MyFuseboxProxy instance.
4. You do not include the code of the getApplication() function from variables.myFusebox , so I dunno what would happen next, but this is not what you want to be happening.

Anyway, the crux is - I think - that instead of running the functions inside variables.myFusebox , you're running them in your MyFuseboxProxy instance instead. If you want to do this sort of proxying (and ignoring for a moment you have invoke() specifically for doing this), you need to still call the function in its original context, not reference it in some new context.

I guess you're doing all this horsing around because ColdFusion doesn't like this syntax:

someObject[someMethodName]()

It baulks at the []() notation. However the solution is not this:

someOutOfContextReference = someObject[someMethodName] result = someOutOfContextReference()

It's this:

someObject.someInContextReference = someObject[someMethodName] result = someObject.someInContextReference()

See the subtle difference?

ColdFusion functions are not intrinsically closures, which is what you'd need them to be to work the way you want.