functional-workshop

functional programming principles applied in C#

---

Project maintained by B1tF8er Hosted on GitHub Pages — Theme by mattgraham

Smart Constructors

Smart constructors are just functions that build values of the required type. Yet perform some extra checks when the value is constructed. In this case it is a good practice to set the constructor of a Reference Type as private and expose a function to allow its instantiation.

using System;
using static System.Console;

internal class TestSmartConstructors
{
    internal static void Run()
    {
        HappyPath();
        InvalidName();
        InvalidAge();
    }

    private static void HappyPath()
    {
        var person = SmartPerson.Create("George", 30);
        WriteLine($"Valid person data so all goes well and we can print {person}");
    }

    private static void InvalidName()
    {
        try
        {
            var person = SmartPerson.Create(null, 30);
        }
        catch (ArgumentNullException ex)
        {
            WriteLine($"{ex.Message}");
        }
    }

    private static void InvalidAge()
    {
        try
        {
            var person = SmartPerson.Create("George", -1);
        }
        catch (ArgumentOutOfRangeException ex)
        {
            WriteLine($"{ex.Message}");
        }
    }
}

internal class SmartPerson
{
    internal string Name { get; }
    internal int Age { get; }

    private SmartPerson(string name, int age) =>
        (Name, Age) = (name, age);

    internal static SmartPerson Create(string name, int age)
    {
        GuardName(name);
        GuardAge(age);

        return new SmartPerson(name, age);
    }

    private static void GuardName(string name)
    {
        if (string.IsNullOrWhiteSpace(name))
            throw new ArgumentNullException(nameof(name), "Name can't be null, empty or white spaces");
    }

    private static void GuardAge(int age)
    {
        if (age < 0 || age > 120)
            throw new ArgumentOutOfRangeException(nameof(age), "Age is not in valid range");
    }

    public override string ToString() => $"My name is {Name} and I am {Age} years old";
}