C# Feature – Primary constructors

Overview

Primary constructors let you declare constructor parameters directly on classes/structs, reducing boilerplate.

Introduced In

C# 12 (2023)

Before

class Order
{
  public int Id { get; }
  public Order(int id) { Id = id; }
}

After

class Order(int id)
{
  public int Id { get; } = id;
}

Annotated Example

record User(string Id, string Email);

Longer Example

// A simple data carrier using a primary constructor
public class Rabbit(string name, int age, double weight, string color, string breed, bool isDomesticated)
{
  public string Name { get; set; } = name;
  public int Age { get; set; } = age;
  public double Weight { get; set; } = weight;
  public string Color { get; set; } = color;
  public string Breed { get; set; } = breed;
  public bool IsDomesticated { get; set; } = isDomesticated;

  public void Print()
  {
    Console.WriteLine($"Name: {Name}");
    Console.WriteLine($"Age: {Age}");
    Console.WriteLine($"Weight: {Weight}");
    Console.WriteLine($"Color: {Color}");
    Console.WriteLine($"Breed: {Breed}");
    Console.WriteLine($"IsDomesticated: {IsDomesticated}");
  }
}

// Usage
var rabbit = new Rabbit("Bugs", 2, 2.5, "Brown", "Holland Lop", true);
rabbit.Print();

Gotchas & Best Practices

• Keep the constructor small; move logic to methods as needed.

Further learning

• Video: Primary Constructors overview (YouTube) — https://www.youtube.com/watch?v=72nt0Ds2478&t=3s

Related Features

• Records
• Required members
• Pattern Matching & Records

Version Notes

• Works with required and init.