C# 8.0 preview in VS 2019 (16.0) の注意点

SwitchExpressionInVs16_0.cs

struct X
{
    public int Value;
    public X(int value) => Value = value;

    // + と & で全く同じ処理を書いとく
    public static X operator +(X x, X y) => new X(x.Value + y.Value);
    public static X operator &(X x, X y) => new X(x.Value + y.Value);

    public static explicit operator X(int x) => new X(x);
    public void Deconstruct(out int x) => x = Value;
    public override string ToString() => Value.ToString();
}

class Program
{
    static void Main()
    {
        var x = new X(1);
        var y = new X(2);

        // + か & か以外は全く同じ
        var add = x + y switch { X(2) => (X)10, X(3) => (X)20, _ => default };
        var and = x & y switch { X(2) => (X)10, X(3) => (X)20, _ => default };

        System.Console.WriteLine(add); // 今、 + の方が優先度高い → 20 (次(VS 16.1)のプレビューで変更予定。11 になる)
        System.Console.WriteLine(and); // switch の方が優先度高い → 11
    }
}