C# 11 List Pattern Examples

listPatternExamples.cs

namespace ListPatterns
{
    internal class Program
    {
        static void Main(string[] args)
        {
            int[] numbers = { 1, 2, 3, 4};

            Console.WriteLine("constant and relational patterns");
            Console.WriteLine(numbers is [1, 2, 3, 4]);                 // True as exact match
            Console.WriteLine(numbers is [1, 2, 3]);                    // False as length is wrong
            Console.WriteLine(numbers is [1, 2, 3, 4, 5]);              // False as length is wrong
            Console.WriteLine(numbers is [0 or 1, <= 2, >= 3, >= 3]);   // True as first element is 1,
                                                                        // second element is less than or equal to 2,
                                                                        // third element is greater than or equal to 3 and
                                                                        // fourth element is greater than or equal to 3

            Console.WriteLine(string.Empty);
            Console.WriteLine("discard patterns");
            Console.WriteLine(numbers is [1, 2, _, 4]);                 // true as position 1, 2, 4 are matching
            Console.WriteLine(numbers is [1, 2, 3, _]);                 // true as position 1,2,3 are matching
            Console.WriteLine(numbers is [1, _, _, 4]);                 // true as position 1 and 4 are matching
            Console.WriteLine(numbers is [1, _, _, 4, _]);              // false as length is not matching
            Console.WriteLine(numbers is [_]);

            Console.WriteLine(string.Empty);
            Console.WriteLine("range patterns");
            Console.WriteLine(numbers is [.., 4]);                      // true as 4 is last element
            Console.WriteLine(numbers is [1, ..]);                      // true as 1 is first element
            Console.WriteLine(numbers is [1, .., 4]);                   // true as the range is from 1 - 4
            Console.WriteLine(numbers is [.., 4, _]);                   // false as 4 is not the 2nd last item

            Console.WriteLine(string.Empty);
            Console.WriteLine("var patterns");
            if (numbers is [_,var secondNumber,..]){
                Console.WriteLine($"The second number is {secondNumber }");
            }
        }
    }
}