Drill 23: Key term — Interfaces and polymorphism

public interface IPrintable
{
    string Render();
}

public record Course(string Slug, string Title) : IPrintable
{
    public string Render() => Title;
}

public record Lesson(string Title, int Minutes) : IPrintable
{
    public string Render() => Title + " (" + Minutes + " min)";
}

public class Report
{
    private readonly IPrintable[] items;

    public Report(IPrintable[] items)
    {
        this.items = items;
    }

    public void Print()
    {
        foreach (var item in items)
        {
            Console.WriteLine(item.Render());
        }
    }
}

var report = new Report(new IPrintable[]
{
    new Course("csharp", "C# Foundations"),
    new Lesson("Variables", 12),
});
report.Print();