What is Pattern Matching in C# 7.0?

C# 7.0 introduces pattern matching in two cases, the is expression and the switch statement.

Patterns test that a value has a certain shape, and can extract information from the value when it has the matching shape.

Pattern matching provides more concise syntax for algorithms

You can perform pattern matching on any data type, even your own, whereas with if/else, you always need primitives to match.

Pattern matching can extract values from your expression.

Before Pattern Matching −

Example

public class PI{
   public const float Pi = 3.142f;
}
public class Rectangle : PI{
   public double Width { get; set; }
   public double height { get; set; }
}
public class Circle : PI{
   public double Radius { get; set; }
}
class Program{
   public static void PrintArea(PI pi){
      if (pi is Rectangle){
         Rectangle rectangle = pi as Rectangle;
         System.Console.WriteLine("Area of Rect {0}", rectangle.Width * rectangle.height);
      }
      else if (pi is Circle){
         Circle c = pi as Circle;
         System.Console.WriteLine("Area of Circle {0}", Circle.Pi * c.Radius * c.Radius);
      }
   }
   public static void Main(){
      Rectangle r1 = new Rectangle { Width = 12.2, height = 33 };
      Rectangle r2 = new Rectangle { Width = 12.2, height = 44 };
      Circle c1 = new Circle { Radius = 12 };
      PrintArea(r1);
      PrintArea(r2);
      PrintArea(c1);
      Console.ReadLine();
   }
}

Output

Area of Rect 402.59999999999997
Area of Rect 536.8
Area of Circle 452.44799423217773

After Pattern Matching −

Example

public class PI{
   public const float Pi = 3.142f;
}
public class Rectangle : PI{
   public double Width { get; set; }
   public double height { get; set; }
}
public class Circle : PI{
   public double Radius { get; set; }
}
class Program{
   public static void PrintArea(PI pi){
      if (pi is Rectangle rectangle){
         System.Console.WriteLine("Area of Rect {0}", rectangle.Width *
         rectangle.height);
      }
      else if (pi is Circle c){
         System.Console.WriteLine("Area of Circle {0}", Circle.Pi * c.Radius *
         c.Radius);
      }
   }
   public static void Main(){
      Rectangle r1 = new Rectangle { Width = 12.2, height = 33 };
      Rectangle r2 = new Rectangle { Width = 12.2, height = 44 };
      Circle c1 = new Circle { Radius = 12 };
      PrintArea(r1);
      PrintArea(r2);
      PrintArea(c1);
      Console.ReadLine();
   }
}

Output

Area of Rect 402.59999999999997
Area of Rect 536.8
Area of Circle 452.44799423217773