Object-Oriented C#

Composition over Inheritance

Assemble behavior from collaborating objects.

Introduction

Composition keeps classes focused and avoids rigid inheritance hierarchies.

Order delegates price calculation to its line items. Each object owns one clear responsibility.

Runnable C# example

Program.cs

using System;
using System.Collections.Generic;
using System.Linq;

record LineItem(string Name, decimal Price);
class Order
{
    public List<LineItem> Items { get; } = new();
    public decimal Total => Items.Sum(item => item.Price);
}

class Program
{
    static void Main()
    {
        var order = new Order();
        order.Items.Add(new("Book", 30m));
        order.Items.Add(new("Pen", 5m));
        Console.WriteLine(order.Total);
    }
}

Result of running the code

Practice with the debugger

Set a breakpoint on an important assignment or condition, click Debug, and inspect the local values before stepping to the next line.