docs/csharp/language-reference/operators/snippets/patterns/PositionalPattern.cs - main - aprogrammer/dotnet-docs

docs/csharp/language-reference/operators/snippets/patterns/PositionalPattern.cs
97 строк3 KB
Bill Wagner
Cover list patterns (#29154)
26 апр 2022, 18:47
26 апр 2022, 18:47b181812
namespace Patterns;

public static class PositionalPattern
{
    public static void Examples()
    {
        UseIdentifiers();
    }

    // <BasicExample>
    public readonly struct Point
    {
        public int X { get; }
        public int Y { get; }

        public Point(int x, int y) => (X, Y) = (x, y);

        public void Deconstruct(out int x, out int y) => (x, y) = (X, Y);
    }

    static string Classify(Point point) => point switch
    {
        (0, 0) => "Origin",
        (1, 0) => "positive X basis end",
        (0, 1) => "positive Y basis end",
        _ => "Just a point",
    };
    // </BasicExample>

    // <MatchTuple>
    static decimal GetGroupTicketPriceDiscount(int groupSize, DateTime visitDate)
        => (groupSize, visitDate.DayOfWeek) switch
        {
            (<= 0, _) => throw new ArgumentException("Group size must be positive."),
            (_, DayOfWeek.Saturday or DayOfWeek.Sunday) => 0.0m,
            (>= 5 and < 10, DayOfWeek.Monday) => 20.0m,
            (>= 10, DayOfWeek.Monday) => 30.0m,
            (>= 5 and < 10, _) => 12.0m,
            (>= 10, _) => 15.0m,
            _ => 0.0m,
        };
    // </MatchTuple>

    private static void UseIdentifiers()
    {
        // <UseIdentifiers>
        var numbers = new List<int> { 1, 2, 3 };
        if (SumAndCount(numbers) is (Sum: var sum, Count: > 0))
        {
            Console.WriteLine($"Sum of [{string.Join(" ", numbers)}] is {sum}");  // output: Sum of [1 2 3] is 6
        }
        
        static (double Sum, int Count) SumAndCount(IEnumerable<int> numbers)
        {
            int sum = 0;
            int count = 0;
            foreach (int number in numbers)
            {
                sum += number;
                count++;
            }
            return (sum, count);
        }
        // </UseIdentifiers>
    }

    // <WithTypeCheck>
    public record Point2D(int X, int Y);
    public record Point3D(int X, int Y, int Z);

    static string PrintIfAllCoordinatesArePositive(object point) => point switch
    {
        Point2D (> 0, > 0) p => p.ToString(),
        Point3D (> 0, > 0, > 0) p => p.ToString(),
        _ => string.Empty,
    };
    // </WithTypeCheck>

    // <WithPropertyPattern>
    public record WeightedPoint(int X, int Y)
    {
        public double Weight { get; set; }
    }

    static bool IsInDomain(WeightedPoint point) => point is (>= 0, >= 0) { Weight: >= 0.0 };
    // </WithPropertyPattern>

    static void CompletePositionPattern(object input)
    {
        // <CompletePositionalPattern>
        if (input is WeightedPoint (> 0, > 0) { Weight: > 0.0 } p)
        {
            // ..
        }
        // </CompletePositionalPattern>
    }
}