Check if any function succeeds, but execute all

Question

What is an elegant (easy to extend as there might be more functions than just A and B) way to implement the following pseudocode?

1. Execute A()
2. Execute B()
3. If A or B succeeded, then do C()

The simple code

if (A() || B())
    C();

won't work because in this case, if A() succeeds, B() isn't executed.

Answer 1

Just use logical or operator:

(Use one | instead of ||)

using System;

public class Program
{
    public static bool A(){
        Console.WriteLine("A");
        return true;
    }
    public static bool B(){
        Console.WriteLine("B");
        return true;
    }
    public static void Main()
    {
        if(A() | B())
        Console.WriteLine("Hello World");
    }
}

// Output:
// A
// B
// Hello World

You can run with .NET Fiddle.

Answer 2

Use “or” that is not short circuited- | (MSDN:Operator or).

The | operator evaluates both operands even if the first operand evaluates to true, so that the result must be true regardless of the value of the second operand.

While using this | operator does exactly what requested in the question it may not be good idea to write in code that needs to be maintained. The | is commonly used as "bitwise or" and most people don't know that in C# it is also defined for Boolean values as "non short-circuiting or". If you decide to use it the code consider adding comment and ideally add unit test that verifies the behavior needed.

For regular code I'd capture results of all methods first and than see if there are any true values.

var results = new[] { M1(), M2(), M3(), M4() };
if (results.Any())
{ … }

Answer 3

Suppose that we have three functions as below:

public static void A() => Console.WriteLine("A");

public static void B() => Console.WriteLine("B");

public static void C() => Console.WriteLine("C");

You can use the following approach:

var task = Task.Run(A)
                .ContinueWith(t => B(), TaskContinuationOptions.NotOnFaulted)
                .ContinueWith(t => C(), TaskContinuationOptions.NotOnFaulted);

task.Wait();

Which will executes the A() and if it executes successfully, then will execute B() and if it succeeded to then C() will be executed. If any exception occurred while executing A() or B(), the children tasks will not be executed.

Thanks to @AlexeiLevenkov, if these methods are doing some CPU intensive works, then paralleling them will give you notable performance benefits, otherwise paralleling might have negative impact on your work!

Microsoft says:

When parallelizing any code, including loops, one important goal is to utilize the processors as much as possible without over parallelizing to the point where the overhead for parallel processing negates any performance benefits

Read more here: https://learn.microsoft.com/en-us/dotnet/standard/parallel-programming/how-to-write-a-simple-parallel-for-loop#matrix-and-stopwatch-example