Explain init-only setters and required members in modern C#

Init-only setters make a property settable only during object initialisation:

public record Order {
    public Guid Id { get; init; }
    public string Email { get; init; } = "";
}

var o = new Order { Id = Guid.NewGuid(), Email = "a@b.com" };
o.Email = "new"; // ❌ compile error

Required members enforce that callers MUST set them in an object initializer:

public record User {
    public required string Email { get; init; }
    public required string Name  { get; init; }
}

var u = new User { Email = "a@b.com" };  // ❌ compile error — Name not set
var u = new User { Email = "a@b.com", Name = "A" };  // ✓

Together they replace ~80% of constructor boilerplate while keeping objects immutable and explicit.

Caveat: required works at compile time only — reflection / serializers won't enforce it. Use Zod/DataAnnotations validation for runtime contracts.