C# 6 feature - using static directive

In C# 6 was introduced using static directive. By using this language construct you can reference to static class members without specifying a type name.

Usage:

using static <fully-qualified-type-name>;

This feature can be really helpful when you want to create a simple console application to test something. Instead of using Console.*** all the time you can speed up the development process by using using static System.Console and after that, you can use static methods defined in the Console class.

In the following examples you can see simple app without and with using using static directive.

using System;
static void Main(string[] args)
{
    Console.WriteLine("Please enter some number:");
    var input = Console.ReadLine();
    if (!string.IsNullOrEmpty(input) && int.TryParse(input, out var number))
    {
        if (number > 0)
            Console.WriteLine("Positive number");
        else if (number == 0)
            Console.WriteLine("Zero");
        else
            Console.WriteLine("Negative number");
    }
    else
    {
        Console.WriteLine("Invalid input!");
    }
}

using static System.Console;
using static System.String;
static void Main(string[] args)
{
    WriteLine("Please enter some number:");
    var input = ReadLine();
    if (!IsNullOrEmpty(input) && int.TryParse(input, out var number))
    {
        if (number > 0)
            WriteLine("Positive number");
        else if (number == 0)
            WriteLine("Zero");
        else
            WriteLine("Negative number");
    }
    else
    {
        WriteLine("Invalid input!");
    }
}

Another interesting case can be class Math which is static class. Let’s say that you want to calculate area of the circle. Without using using static directive you write following code Math.PI * Math.Pow(Radius, 2) but when you add to your using statements using static System.Math; you can write previous code as PI * Pow(Radius, 2).

Let’s jump to another example. We want to calculate the area of a circular segment. As you will see in the example using using static directive improve math formula readability. We’re going to use the following formula to calculate.

\[A = {\alpha \over 360} \pi r^2 - {r^2 \sin(\alpha) \over 2} \]

Below is implementation of this formula in C#. First of them using using static directive (the code is simpler and more readable than the other one).

using static System.Math;
...
double degress = 120.0;
double radius = 8.0;
double angle = PI * degress / 180.0;
var area = ((degress / 360.0) * PI * Pow(radius, 2)) - (Pow(radius, 2) * Sin(angle) / 2);

double degress = 120.0;
double radius = 8.0;
double angle = PI * degress / 180.0;
var area = (degress / 360.0) * Math.PI * Math.Pow(radius, 2))
            - ((Math.Pow(radius, 2) * Math.Sin(angle)) / 2);

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