NETCore3Demo/ConsoleApp2/Program.cs

using System;

namespace ConsoleApp2
{
    class Program
    {
        delegate double Function(double x);
        static void Main(string[] args)
        {
            double[] a = { 0.0, 0.5, 1.0 };
            //double[] squares = Apply(a, Square);
            //double[] sines = Apply(a,  Math.Sin);
            double[] squares = Apply(a, new Function(Square));
            double[] sines = Apply(a, new Function(Math.Sin));
            Multiplier m = new Multiplier(2.0);
            double[] doubles = Apply(a, m.Multiply);
        }
        static double Square(double x)
        {
            return x * x;
        }
        static double[] Apply(double[] a, Function f)
        {
            double[] result = new double[a.Length];
            for (int i = 0; i < a.Length; i++) {
                result[i] = f(a[i]);
            }
            return result;
        }
    }
    class Multiplier
    {
        double factor;
        public Multiplier(double factor)
        {
            this.factor = factor;
        }
        public double Multiply(double x)
        {
            return x * factor;
        }
    }
}