"Inline Struct Field Initialization With Multiple Constructors"

public readonly struct User {
	public readonly string Name;
	public readonly int Age = -1;

	public User(string name) => Name = name;

	public User(string name, int age) {
		Name = name;
		Age = age;
	}
}

// ...

var u = new User("Ben");
Console.WriteLine(u.Name + " " + u.Age);