Pattern matching: switch expressions, property patterns, when guards?

// Раньше
string Describe(object shape)
{
    if (shape is Circle)
    {
        var c = (Circle)shape;
        return $"Круг R={c.Radius}";
    }
    else if (shape is Rectangle)
    {
        var r = (Rectangle)shape;
        if (r.Width == r.Height) return $"Квадрат {r.Width}";
        return $"Прямоугольник {r.Width}x{r.Height}";
    }
    return "Неизвестно";
}

// Сейчас
string Describe(object shape) => shape switch
{
    Circle { Radius: var r }                          => $"Круг R={r}",
    Rectangle { Width: var w, Height: var h } when w == h => $"Квадрат {w}",
    Rectangle(var w, var h)                           => $"Прямоугольник {w}x{h}",
    null                                              => "null",
    _                                                 => "Неизвестно"
};

public enum OrderStatus { New, Paid, Shipped, Delivered, Cancelled }

public decimal CalculateShipping(Order order) => order switch
{
    { Status: OrderStatus.Cancelled }                      => 0m,
    { Customer.IsPremium: true }                           => 0m,
    { Total: >= 5000 }                                     => 0m,
    { Weight: > 20, Destination.Country: not "UZ" }        => 450m,
    { Weight: > 20 }                                       => 150m,
    { Destination.Country: "UZ" }                          => 50m,
    _                                                      => 200m
};

string Label(OrderStatus s) => s switch
{
    OrderStatus.New     => "Новый",
    OrderStatus.Paid    => "Оплачен",
    OrderStatus.Shipped => "Отправлен",
};
// warning CS8509: The switch expression does not handle all possible values
// в рантайме для Delivered: SwitchExpressionException

var result = request switch
{
    { Amount: <= 0 }                                        => Result.Fail("Сумма должна быть положительной"),
    { Currency: var c } when !_supported.Contains(c)        => Result.Fail($"Валюта {c} не поддерживается"),
    { From: var from, To: var to } when from == to          => Result.Fail("Счета совпадают"),
    _                                                       => Result.Ok()
};

// Позиционный: через Deconstruct (есть у record и кортежей)
string Quadrant(Point p) => p switch
{
    (0, 0)            => "Начало координат",
    (> 0, > 0)        => "I",
    (< 0, > 0)        => "II",
    (< 0, < 0)        => "III",
    (> 0, < 0)        => "IV",
    _                 => "На оси"
};

// Кортежи: машина состояний без вложенных if
State Next(State current, Command cmd) => (current, cmd) switch
{
    (State.Draft,    Command.Submit)  => State.Review,
    (State.Review,   Command.Approve) => State.Published,
    (State.Review,   Command.Reject)  => State.Draft,
    (_,              Command.Archive) => State.Archived,
    _ => throw new InvalidOperationException($"Нельзя {cmd} из {current}")
};

// Списковые (C# 11)
string Parse(string[] args) => args switch
{
    []                         => "Нет аргументов",
    ["--help" or "-h"]         => "Справка",
    ["run", var file]          => $"Запуск {file}",
    ["run", var file, .. var rest] => $"Запуск {file} с {rest.Length} опциями",
    _                          => "Неизвестная команда"
};