Read/Write-Only Properties

Part of the Object Oriented Programming section of Coddy's C# journey — lesson 11 of 70.

Sometimes you need properties that can only be read or only be written. You can control this by using private on individual accessors.

A read-only property has a public getter but a private setter (or no setter at all):

public class User
{
    public string Username { get; private set; }
    
    public User(string username)
    {
        Username = username;
    }
}

External code can read Username, but only the class itself can modify it. This is useful for values that should be set once during construction.

A write-only property has a public setter but a private getter:

public class Account
{
    public string Password { private get; set; }
    
    public bool ValidatePassword(string input)
    {
        return input == Password;
    }
}

Write-only properties are rare but useful for sensitive data like passwords, where you want to accept input without exposing the stored value.

You can also create truly read-only properties with only a getter:

public class Circle
{
    public double Radius { get; }
    public double Area => Math.PI * Radius * Radius;
    
    public Circle(double radius)
    {
        Radius = radius;
    }
}

Properties with only get; can only be assigned in the constructor or at declaration, making them immutable after object creation.

Challenge

Easy

Let's build a secure configuration system that demonstrates when to use read-only and write-only properties to protect sensitive data.

You'll create two files to organize your code:

Config.cs: Define a ServerConfig class in the Settings namespace that manages server configuration. It should have:
- A read-only property ServerName (can only be set in the constructor)
- A read-only property Port with a private setter (set via constructor)
- A write-only property ApiKey that stores a secret key internally
- A method ValidateApiKey(string key) that returns true if the provided key matches the stored one
- A constructor that accepts the server name and port
Program.cs: In your main file, create a ServerConfig object using input values, set the API key, then validate it against a test key.

You will receive four inputs:

Server name
Port number
API key to store
API key to validate

Print the server details and validation result in this format:

Server: {ServerName}, Port: {Port}
API Key Valid: {True/False}

For example, if the inputs are MainServer, 8080, secret123, and secret123, the output should be:

Server: MainServer, Port: 8080
API Key Valid: True

Cheat sheet

You can control property access by using private on individual accessors.

Read-only property with a private setter:

public class User
{
    public string Username { get; private set; }
    
    public User(string username)
    {
        Username = username;
    }
}

External code can read Username, but only the class itself can modify it.

Write-only property with a private getter:

public class Account
{
    public string Password { private get; set; }
    
    public bool ValidatePassword(string input)
    {
        return input == Password;
    }
}

Useful for sensitive data where you want to accept input without exposing the stored value.

Truly read-only property with only a getter:

public class Circle
{
    public double Radius { get; }
    
    public Circle(double radius)
    {
        Radius = radius;
    }
}

Properties with only get; can only be assigned in the constructor or at declaration, making them immutable after object creation.

Try it yourself

using System;
using Settings;

class Program
{
    public static void Main(string[] args)
    {
        // Read inputs
        string serverName = Console.ReadLine();
        int port = Convert.ToInt32(Console.ReadLine());
        string apiKeyToStore = Console.ReadLine();
        string apiKeyToValidate = Console.ReadLine();

        // TODO: Create a ServerConfig object with serverName and port

        // TODO: Set the API key using the write-only property

        // TODO: Validate the API key and print the results
        // Format: Server: {ServerName}, Port: {Port}
        //         API Key Valid: {True/False}
    }
}