How to scope closure's variables in CF10?

closures, coldfusion, coldfusion-10, scope

Solution

    function helloTranslator(String helloWord) 
    { 
      return function(String name) 
      { 
        return "#helloWord#, #name#"; 
      }; 
    }

Here `helloWord` and `name` cannot be scoped. There is an implicit `Owner` scope with "closures defined within a function" which is the local scope of declaring (parent) function, where these variables are present. So these variables must be unique (within function) to be accessed from closures.

In closure, search for an unscoped variable goes through:

- Closure's local scope

- Closure's arguments scope

- Outer/Owner function's local scope if available

- Outer/Owner function's argument scope if available

- Variables scope (available at the time of closure's creation)

- ColdFusion built-in scope

If something is scoped as `Local`, in a closure, it would search in 1 only. AFN there is no way to directly scope for 3,4.

p.s. as said earlier `Owner` scope is nothing but an implicit scope which points to a cached copy of parent/outer function's local scope at the time of closure's creation.

p.s. You may log an enhancement with ColdFusion to make this scope explicit.

An example of different scopes is as follows. Run this and you shall understand how closure would use differnt scopes.

any function exampleClosureForm(arg1){

    function x(innerArg1,innerArg2){
        //var arg1= 50;// will hide parent's arg1 if declared
        writedump(arguments);// would dump closure's
        writedump(local);// would dump closure's
        writedump(session.a); // would be same session shared across
        writedump(arg1); // would dump parents argument arg1
        return session.a-- + innerArg1+innerArg2+arg1--;// decrementing to see its behavior for successive call
    };  
    writeoutput(x(1,2));
    writedump(arguments,"browser","html",false,"function");// would dump parent's
    writedump(local,"browser","html",false,"function");// would dump parent's
    arg1 = -100; // since closure is sharing the parent's variable, this change should get reflected
    return x;
}
session.a = 10;
a = exampleClosureForm(10);
writeoutput("now the calls <br>"); 
writeoutput(a(innerArg1=5,innerArg2=5)); 
writeoutput("<br>");
// with argumentcollection
argsColl = structNew();
argsColl.innerArg1= 1;
argsColl.innerArg2= 3;
writeoutput(a(argumentCollection = argsColl));

Problem

Original source