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C# Academy · Lesson

Generic math (overview), generic attributes (when relevant)

Emulate generic math without modern features: pass an ops-provider or delegates, constrain types carefully, and simulate "generic attributes" via Type parameters.

Generic math on C# 6

Goal: Write numeric algorithms generically on C# 6.

  • No static abstract operators on T
  • Workarounds: ops-provider interface or small delegates
  • For annotations, use attributes with Type parameters

Ops-provider pattern

Provide Zero and Add via an interface. The generic algorithm calls those methods instead of using + on T.

using System;
using System.Collections.Generic;

public interface INumericOps<T>
{
  T Zero { get; }
  T Add(T a, T b);
}

public sealed class IntOps : INumericOps<int>
{
  public int Zero { get { return 0; } }
  public int Add(int a, int b) { return a + b; }
}

public sealed class DoubleOps : INumericOps<double>
{
  public double Zero { get { return 0.0; } }
  public double Add(double a, double b) { return a + b; }
}

public class Program
{
  static T Sum<T>(IEnumerable<T> items, INumericOps<T> ops)
  {
    T acc = ops.Zero;
    foreach (T x in items) acc = ops.Add(acc, x);
    return acc;
  }

  public static void Main(string[] args)
  {
    int s1 = Sum(new int[] {1,2,3}, new IntOps());
    double s2 = Sum(new double[] {1.5, 2.0}, new DoubleOps());
    Console.WriteLine("Sum int = " + s1);
    Console.WriteLine("Sum double = " + s2);
  }
}

All lessons in this course

  1. unmanaged, notnull, new() (C# 6 emulation)
  2. Generic math (overview), generic attributes (when relevant)
  3. Reusable generic utilities
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