C# 14 & Modern Syntax — Primary Constructors, field & Null Safety

Combine modern C# syntax with genuine C# 14 features. Primary constructors and collection expressions arrived earlier; C# 14 adds features such as field-backed properties and null-conditional assignment.

• Use a primary constructor to capture constructor parameters in a concise class declaration.
• Use a collection expression for compact collection initialization.
• Use the C# 14 `field` keyword to validate an auto-property without declaring a backing field.
• Use C# 14 null-conditional assignment to update an object only when it is non-null.

Project setup: Create a .NET 10 Console App using C# 14. Visual Studio 2026 with the .NET 10 SDK supports C# 14.

The following example is written specifically for this lesson. Create the project described above, enter the code, run it, and then change some values to observe how the feature behaves.

// Primary constructors were introduced before C# 14,
// but remain useful modern C# syntax.
public sealed class Product(string name, decimal price)
{
    public string Name { get; } = name;

    public decimal Price
    {
        get;
        set => field = value >= 0
            ? value
            : throw new ArgumentOutOfRangeException(nameof(value));
    } = price;

    public DateTime? LastViewed { get; set; }
}

Product keyboard = new("Keyboard", 299.90m);

// Collection expression (modern C# syntax).
Product[] products =
[
    keyboard,
    new Product("Mouse", 99.90m)
];

// C# 14: null-conditional assignment.
Product? selected = products.FirstOrDefault(p => p.Name == "Keyboard");
selected?.LastViewed = DateTime.UtcNow;

foreach (Product product in products)
{
    Console.WriteLine($"{product.Name}: {product.Price:C}");
}

• The primary-constructor parameters `name` and `price` are available in instance-member initializers.
• `field` refers to the compiler-generated backing field for `Price`, so validation can be written without declaring `_price`.
• `selected?.LastViewed = ...` is a C# 14 null-conditional assignment: the right side is used only when `selected` is not null.
• Primary constructors and collection expressions are useful modern syntax but are not new C# 14 features; C# 14 itself also adds extension members, span conversions, partial constructors/events, and other language improvements.

Mini project: create a Student primary-constructor class, validate Mark with the `field` keyword, initialize several students with a collection expression, and conditionally set a nullable LastLogin property with `?.`.

Tip: Type the code yourself in Visual Studio 2026, run it, then deliberately change one part at a time. The goal is to understand the feature rather than simply copy the finished example.

When you are comfortable with this lesson, continue to Lesson 29.