Adobe 38043740 Developing Applications - Page 181

DEVELOPING COLDFUSION 9 APPLICATIONS 176 Building Blocks of ColdFusion Applications Identifying and checking for UDFs You can use the IsCustomFunction function to determine whether a name represents a UDF. The IsCustomFunction function generates an error if its argument does not exist. As a result, ensure that the name exists before calling the function, for example, by calling the IsDefined function. The following code shows this use: if(IsDefined("MyFunc")) if(IsCustomFunction(MyFunc)) WriteOutput("MyFunc is a user-defined function"); else WriteOutput("Myfunc is defined but is NOT a user-defined function"); else WriteOutput("MyFunc is not defined"); You do not surround the argument to IsCustomFunction in quotation marks, so you can use this function to determine if function arguments are themselves functions. Using the Evaluate function If your user-defined function uses the Evaluate function on arguments that contain strings, Make sure that all variable names you use as arguments include the scope identifier. Doing so avoids conflicts with function-only variables. The following example returns the result of evaluating its argument. It produces the expected results, the value of the argument, if you pass the argument using its fully scoped name, Variables.myname. However, the function returns the value of the function local variable if you pass the argument as myname, without the Variables scope identifier. myname = "globalName"; function readname(name) { var myname = "localName"; return (Evaluate(name)); } The result of calling readname with myname is: #readname("myname")# The result of calling readname with Variables.myname is: #readname("Variables.myname")# Using recursion A recursive function is a function that calls itself. Recursive functions are useful when an algorithm that repeats the same operation multiple times using the results of the preceding repetition can solve the problem. Factorial calculation, used in the following example, is one case where recursion is useful. The Towers of Hanoi game is also solved using a recursive algorithm. A recursive function, like looping code, must have an end condition that always stops the function. Otherwise, the function continues until a system error occurs or you stop the ColdFusion server. The following example calculates the factorial of a number, that is, the product of all the integers from 1 through the number; for example, 4 factorial is 4 X 3 X 2 X 1 = 24. Last updated 1/20/2012