Passing user defined methods to methods

Question

In my class library I have methods that need to work on methods defined by the user. For example I have a method M() in my library which needs a function double f(double x) this function f() has to be defined by the user. In fact different users will have different f()'s. In C you an pass this in the parameter list. What is the best way to do this in C#?

Administrator · Answer

I am thinking the following: Declare a nested class within my class1 called class Function. This class contains an Interface with the function F() in the Interface. I am not sure how this would be called from the user class Class2. Any suggestions. Mike

Administrator · Answer

Thanks for the insight. I am still a little puzzled please bear with me. I am thinking along the following lines: // Class library written by me with a method M() class Class1 { //Method public double M(parameters) { // The function double f(double x) from user. z1 = f(x1); // Other computations return z; } // Other methods. } //The user writes the exec class class Class2 { // Two possible functions // The only restriction is it has the form double f(double x) private double foo1(double x) { return x/2; } private double foo2(double x) { return x**2; } static void main (string[] args) { // Now call method M() of Class1 x = Class1.M(use foo1()) y = Class1.M(use foo2()) Console.Out.WriteLine (xy); } } Will a delegate work this way? Another possibility I think is to have public doble virtual f(double x) { return 0; } Then do an overide in the exec class. However it would not work with two functions. Another idea was to have an inner class in Class1 which included an interface with f() as an interface method. As you see I am a little mixed up.

Administrator · Answer

You are talking about function pointers? They are called delegates in C#. Here is a simple example. Remeber delegates are strictly type safe so parameter types and return values have to match. (which is not the case with C that lets you do whatever tricks) class Class1 { // Define what kind of method will be called private delegate double MyFunc(double d); // This is the real function that will be called that is written by your users private static double foo(double x) { return x/2; } [STAThread] static void Main(string[] args) { // Create an instance of delegate // And give it a pointer to the method MyFunc f = new MyFunc(Class1.foo); // Call the actual method through delegate double result = f(5); Console.Out.WriteLine(Result :  + result.ToString()); } }