Primary Constructors & Object Initializers

In C# 12, Microsoft introduced Primary Constructors for classes and structs, effectively making code cleaner and reducing the amount of redundant "assigning parameters to private fields" we’ve done for decades.

1. Eliminate Constructor Bloat

In legacy C#, 50% of your class was just boilerplate for Dependency Injection. Primary constructors allow you to define parameters directly on the class header.

public class Service 
{
    private readonly IRepository _repo;
    public Service(IRepository repo) 
    {
        _repo = repo;
    }
}

// The parameter 'repo' is available throughout the whole class body!
public class Service(IRepository repo) 
{
    public async Task DoWork() => await repo.Save();
}

2. Required Properties & Object Initializers

Sometimes you don't want a constructor at all, but you want to FORCE the developer to set a property when they create the object. We use the required keyword.

public class User 
{
    public required string Email { get; init; }
    public string? OptionalNickName { get; set; }
}

// ❌ ERROR: Compiler yells because 'Email' was not set
var u = new User();

// ✅ GOOD
var u = new User { Email = "sandeep@example.com" };

4. Interview Mastery

Q: "If I use a Primary Constructor on a class, why can't I access the parameter from outside the class instance?"

Architect Answer: "Primary constructor parameters in classes are NOT properties or fields; they are purely parameters with a 'Class-wide' scope. The compiler captures them privately. If you want a primary constructor parameter to be publicly visible, you must manually assign it to a public property inside the class body. This is a deliberate security feature to avoid 'accidental exposure' of injected services (`DbContext`, `Logger`) which should remain private internal implementation details."