Conditional

In C#, a Conditional method is not always executed. It is compiled into the program only when certain symbols are defined with #define.

The Conditional attribute enables conditional compilation. It accepts a string argument—this is the symbol that must be defined for the method to be compiled.

This example program contains a MethodA, which is conditional on the symbol PERLS. It also contains MethodB, which is conditional on the symbol DOT.

Note At the top of the program, you can see 2 preprocessor directives. The symbol PERLS is defined. The symbol DOT is not.

Note 2 The execution of the program shows that MethodA is executed, but MethodB is not.

Detail It isn't possible to use Conditional on methods that return a value. Methods must be used in the void context.

And This is because variables can be assigned to method return values. You can work around this limitation using parameters.

#define PERLS
#undef DOT
using System;
using System.Diagnostics;

class Program
{
    static void Main()
    {
        MethodA();
        MethodB();
    }

    [Conditional("PERLS")]
    static void MethodA()
    {
        Console.WriteLine(true);
    }

    [Conditional("DOT")]
    static void MethodB()
    {
        Console.WriteLine(false);
    }
}
True

Conditional `List`

It is possible to modify a collection in DEBUG mode. You can add strings or other values conditionally—when debugging your application, not when it's deployed.

Info The program defines an AddToArray method, which simply adds two elements to the array. It uses the Conditional("DEBUG") attribute.

Detail This means to only compile the method if DEBUG is defined. The Conditional attribute requires System.Diagnostics.

using System;
using System.Collections.Generic;
using System.Diagnostics;

class Program
{
    static void Main()
    {
        List<string> l = new List<string>();
        l.Add("rabbit");
        l.Add("bird");
        AddToArray(l);
        Console.WriteLine("Elements: {0}", l.Count);
    }

    [Conditional("DEBUG")]
    static void AddToArray(List<string> l)
    {
        // New array
        string[] a = new string[2];
        a[0] = "cat";
        a[1] = "mouse";
        // Add array to end of list
        l.AddRange(a);
    }
}
Elements: 4
Elements: 2

You can encapsulate your DEBUG-specific logic in separate Conditional("DEBUG") methods. This improves code clarity and performance, and reduces complexity.

Conditional allows us to create a method whose existence depends on a preprocessor directive. The Conditional attribute fits with the clear syntax of the C# language.

Conditional

Conditional List

Conditional `List`