Function wraps another function

Question

I have a set of static functions like

internal static List<ClassA> GetListOfClassA (int id, string name) {...}
internal static string GetName (int id) {...}
internal static List<ClassB> GetCompleteListOfClassB() {...}

What I would like to accomplish here is the following (written as pseudocode)

List<ClassA> newList = new List<ClassA>;
string newname;
List<ClassB> newListB = new List<ClassB>;

Pipe (newList = GetListOfClassA (5, "myname"));
Pipe (newname = GetName (5));
Pipe (newListB = GetCompleteListOfClassB());

Pipe should be a function that accepts another function with parameters, executes some code and allows to return the value of the function to the caller. Pipe should do something like

{
 Console.WriteLine ("Test");
 if (CertainCondition==true)
     return GetName (value);
 else 
    wait(250);
}

I tried all kind of things like lambda expressions or actions but I can't get it to work generically so that all kinds of functions are accepted.

Answer 1

It would work when you did it like this:

List<ClassA> newList = new List<ClassA>();
string newname;
List<ClassB> newListB = new List<ClassB>();

newList = Pipe(() => GetListOfClassA(5, "myname"));
newname = Pipe(() => GetName(5));
newListB = Pipe(() => GetCompleteListOfClassB());

You can implement Pipe like this:

public static T Pipe<T>(Func<T> action)
{
    Console.WriteLine("Entering pipe");
    if (someCondition)
        return action();
    else
    {
        // do something else; but you still need to return something
        return default(T);
    }
}

You could also implement it as a function that does not return anything on its own but requires an Action that has a side effect (e.g. setting a variable):

Pipe(() => newList = GetListOfClassA(5, "myname"));
Pipe(() => newname = GetName(5));
Pipe(() => newListB = GetCompleteListOfClassB());

The implementation would be very similar except that you do not need to return anything:

public static T Pipe<T>(Func<T> action)
{
    Console.WriteLine("Entering pipe");
    if (someCondition)
        action();
    else
        // do something else
}

The former has the benefit that there is a clear visibility of the side effect, i.e. the variable being set while the latter one leaves you in a situation where the variable could stay unassigned.

Answer 2

My first guess is that Pipe does not pass any arguments to the 'GetName' function.

In that case you can let Pipe accept an Action and use it like

Pipe(() => newList = GetListOfClassA(5, "myname"));