c# - 枚举定义中的加号运算符

Question

我今天偶然发现了枚举定义中加号 (+) 运算符的用法，我很惊讶地看到附带的测试通过了。任何人都知道这可能被记录在哪里？

public enum ApprovalItemState
{
    Enqueued = 1,
    Approved = 2,
    Denied = 4,
    Acknowledged = 8,
    ApprovalAcknowledged = ApprovalItemState.Approved + ApprovalItemState.Acknowledged,
    DenialAcknowledged = ApprovalItemState.Denied + ApprovalItemState.Acknowledged
}


[TestClass]
public class ApprovalItemStateTests
{
    [TestMethod]
    public void AreFlagsDeniedAndAcknowledged()
    {
        Assert.AreEqual(ApprovalItemState.DenialAcknowledged, ApprovalItemState.Denied | ApprovalItemState.Acknowledged);
    }

    [TestMethod]
    public void IsDenialAcknowledged()
    {
        Assert.IsTrue(Enum.IsDefined(typeof(ApprovalItemState), ApprovalItemState.Denied | ApprovalItemState.Acknowledged));
        Assert.AreEqual(ApprovalItemState.Denied | ApprovalItemState.Acknowledged, (ApprovalItemState)Enum.Parse(typeof(ApprovalItemState), "DenialAcknowledged"));
    }


    [TestMethod]
    public void IsNotDeniedAndApproved()
    {
        Assert.IsFalse(Enum.IsDefined(typeof(ApprovalItemState), ApprovalItemState.Approved | ApprovalItemState.Denied));
    }
}

Answer 1

里德的回答当然是正确的。我只是想我会添加一些有趣的琐事。首先，当您在枚举内部时，枚举的所有成员都在范围内。这是 C# 中唯一可以通过非限定名称使用枚举成员的情况!

public enum ApprovalItemState 
{
    Enqueued = 1,
    Approved = 2,
    Denied = 4,
    Acknowledged = 8,
    ApprovalAcknowledged = Approved | Acknowledged,
    DenialAcknowledged =  Denied | Acknowledged 
} 

第二个琐事点是 C# 编译器实际上允许在一个枚举中涉及其他枚举的枚举算术!

enum E
{
    E1
}
enum F
{
    F1
}
enum G
{
    G1 = E.E1 + F.F1
}

通常这根本不合法；您不能将两个不同的枚举相加，也不能分配结果。编译器放宽了枚举初始化程序中的这些规则，以便您可以执行以下操作:

enum MyFlags
{
    MyReadOnly = FileFlags.ReadOnly,
    ...