C#7.0在两种情况下引入了模式匹配,即is表达式和switch语句。
模式测试值具有特定形状,并在其具有匹配形状时可以从值中提取信息。
模式匹配为算法提供了更简洁的语法
您可以对任何数据类型(甚至您自己的数据类型)执行模式匹配,而使用if / else则始终需要基元进行匹配。
模式匹配可以从表达式中提取值。
模式匹配之前-
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(); } }
输出结果
Area of Rect 402.59999999999997 Area of Rect 536.8 Area of Circle 452.44799423217773
模式匹配后-
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(); } }
输出结果
Area of Rect 402.59999999999997 Area of Rect 536.8 Area of Circle 452.44799423217773