C# Academy · Lesson

init-Only Setters

Create properties settable only at initialization.

init-Only Setters is a free C# Academy lesson on CoddyKit — lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the C# Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

init-Only Setters

An init accessor lets a property be set during object construction (including object initializers) but makes it read-only afterward. The shape is { get; init; }.

using System;

class Point {
    public int X { get; init; }
    public int Y { get; init; }
}

var p = new Point { X = 3, Y = 4 };
Console.WriteLine(p.X + "," + p.Y); // 3,4

Set Only at Initialization

After the object is built, assigning to an init property is a compile error, guaranteeing immutability post-construction.

using System;

class Config {
    public string Name { get; init; }
}

var c = new Config { Name = "prod" };
// c.Name = "dev"; // compile error
Console.WriteLine(c.Name); // prod

Object Initializers Still Work

The big win over a read-only get-only property is that init supports the object initializer syntax, so you do not need a constructor for every property.

using System;

class Settings {
    public bool DarkMode { get; init; }
    public int FontSize { get; init; }
}

var s = new Settings { DarkMode = true, FontSize = 14 };
Console.WriteLine(s.DarkMode + " " + s.FontSize); // True 14

Combining with Constructors

You can set init properties from a constructor and also allow initializer overrides.

using System;

class User {
    public string Role { get; init; } = "guest";
    public User() { }
}

var u = new User { Role = "admin" };
Console.WriteLine(u.Role); // admin

Default Values

init properties can have default initializers that apply unless overridden during construction.

using System;

class Options {
    public int Retries { get; init; } = 3;
}

Console.WriteLine(new Options().Retries);            // 3
Console.WriteLine(new Options { Retries = 5 }.Retries); // 5

init vs set

A set accessor allows mutation any time; init restricts assignment to the construction phase. Choose init for immutable-after-creation data.

using System;

class Mutable { public int V { get; set; } }
class Frozen  { public int V { get; init; } }

var m = new Mutable { V = 1 };
m.V = 2; // allowed
Console.WriteLine(m.V); // 2

init with Validation

You can implement an explicit init body with a backing field to validate the assigned value.

using System;

class Percentage {
    private int _value;
    public int Value {
        get => _value;
        init => _value = (value < 0 || value > 100)
            ? throw new ArgumentOutOfRangeException()
            : value;
    }
}

Console.WriteLine(new Percentage { Value = 80 }.Value); // 80

init in Records

Positional record properties are init-only by default, which is why records are immutable yet support with copies.

using System;

record Account(string Id, decimal Balance);

var a = new Account("A1", 100m);
Console.WriteLine(a.Balance); // 100

Nested Object Initializers

init works with nested object initializers, letting you build complex immutable graphs in one expression.

using System;

class Address { public string City { get; init; } }
class Person { public string Name { get; init; } public Address Home { get; init; } }

var p = new Person { Name = "Lin", Home = new Address { City = "Oslo" } };
Console.WriteLine(p.Name + " / " + p.Home.City); // Lin / Oslo

init and Inheritance

Derived classes can set base init properties via object initializers, since the construction phase spans the whole object.

using System;

class Base { public int Id { get; init; } }
class Item : Base { public string Name { get; init; } }

var i = new Item { Id = 1, Name = "Pen" };
Console.WriteLine(i.Id + " " + i.Name); // 1 Pen

Putting It Together

An immutable DTO built entirely with init properties and an object initializer.

using System;

class OrderDto {
    public int Id { get; init; }
    public string Customer { get; init; }
    public decimal Amount { get; init; }
}

var o = new OrderDto { Id = 7, Customer = "Ada", Amount = 49.9m };
Console.WriteLine(o.Id + " " + o.Customer + " " + o.Amount); // 7 Ada 49.9

Quick Check

Test your understanding of init-only setters.

Recap

You learned init-only setters.

{ get; init; } allows assignment only during construction.
Object initializers work with init properties.
You can add validation via an explicit init body.
Record positional properties are init by default.

Frequently asked questions

Is the “init-Only Setters” lesson free?

Yes — the full text of “init-Only Setters” is free to read here on the web, and the C# Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the C# Academy course, upgrade to CoddyKit PRO.

What will I learn in “init-Only Setters”?

Create properties settable only at initialization. You practise C# Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start C# Academy?

No prior experience is required. C# Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “init-Only Setters” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this C# Academy lesson?

Yes. Every C# Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

← Back to C# Academy