Enforcing Required Function Calls in C#

The Problem: Unchecked Function Calls

In C#, it’s fairly common to create functions that return a status, helping developers monitor the success or failure of operations. However, a common pitfall is that some developers may ignore these returned statuses entirely. This can lead to unintended consequences if proper error handling isn’t executed.

For instance, consider a Status class, which might contain information about whether an operation is successful or if there were issues during execution:

Status MyFunction()
{
   if(...) // something bad
     return new Status(false, "Something went wrong");
   else
     return new Status(true, "OK");
}

The expectation is that all callers of MyFunction check the returned status:

Status myStatus = MyFunction();
if (!myStatus.IsOK())
   // handle it, show a message,...

Nonetheless, some callers might lazily ignore the status check:

// Ignoring the returned status
MyFunction(); // call function and ignore returned Status

Can This Be Prevented?

This raises an important question: How can we ensure that every caller checks the returned status? In C++, one could utilize a destructor to verify the status at the end of the object’s lifecycle. However, in C#, destructors are generally frowned upon due to the non-deterministic nature of the garbage collector.

The Solution: Using Delegates for Required Function Calls

Although C# lacks the ability to enforce a method return value to be called or checked, an innovative workaround involves the use of delegates. This technique doesn’t just return a value; instead, it requires the caller to process the returned status explicitly through a callback mechanism.

Example Implementation

Let’s look at a simple implementation using delegates:

using System;

public class Example
{
    public class Toy
    {
        private bool inCupboard = false;
        public void Play() { Console.WriteLine("Playing."); }
        public void PutAway() { inCupboard = true; }
        public bool IsInCupboard { get { return inCupboard; } }
    }

    public delegate void ToyUseCallback(Toy toy);

    public class Parent
    {
        public static void RequestToy(ToyUseCallback callback)
        {
            Toy toy = new Toy();
            callback(toy);
            if (!toy.IsInCupboard)
            {
                throw new Exception("You didn't put your toy in the cupboard!");
            }
        }
    }

    public class Child
    {
        public static void Play()
        {
            Parent.RequestToy(delegate(Toy toy)
            {
                toy.Play();
                // Oops! Forgot to put the toy away!
            });
        }
    }

    public static void Main()
    {
        Child.Play();
        Console.ReadLine();
    }
}

Explanation of the Code

In this example, when Parent.RequestToy is called, it expects a callback function that will perform operations with the Toy object. After executing the callback, it checks whether the toy has been put away:

• If the callback doesn’t call toy.PutAway(), an exception is thrown. This ensures that the caller must address the Toy at the end of its usage, effectively enforcing that necessary follow-up operations occur.
• This method doesn’t guarantee the caller will remember to check the status, but it enforces structure in a way that elevates the importance of the operation.

Conclusion

While it may not be possible in C# to enforce checks on returned values as rigorously as in C++, we can leverage delegates to create a pattern that effectively communicates the necessity of further action, enhancing our code’s reliability. Utilizing this pattern both aids in ensuring proper handling of function results while also keeping your programming practices clean and organized.

By implementing this approach, we ensure that the developers using your code cannot easily bypass essential checks. While it might seem a bit unconventional, it serves as a useful way to create a culture of accountability in error handling.