c＃enum equals（）vs ==

Question

In the case of using enums, is it better to use:

if (enumInstance.Equals(MyEnum.SomeValue))

or to use

if (enumInstance == MyEnum.SomeValue)

Are their any important considerations using one vs the other?

Answer 1

If the compile-time type of enumInstance is the enum type, you're fine with == .

If the compile-time type of enumInstance is Enum , ValueType or Object , you need to use Equals . (You'll get a compile-time error if you try to use == in that case.)

Note that your enum currently violates .NET naming conventions - it would normally be MyEnum.Value .

Answer 2

Using == instead of Equals is a bit quicker, there is no need to box enums and no functions calls needed here is sample c# code and generated MSIL for it:

 class Program
    {
        static void Main(string[] args)
        {
            var instance = MyEnum.First;

            if (instance == MyEnum.First)
            {
                Console.WriteLine("== Called");
            }

            if (instance.Equals(MyEnum.First))
            {
                Console.WriteLine("Equals called");
            }

        }     
    }

    enum MyEnum { First = 99, Second = 100}

MSIL:

IL_0000:  nop
  IL_0001:  ldc.i4.s   99
  IL_0003:  stloc.0
  IL_0004:  ldloc.0
  IL_0005:  ldc.i4.s   99
  IL_0007:  ceq
  IL_0009:  ldc.i4.0
  IL_000a:  ceq
  IL_000c:  stloc.1
  IL_000d:  ldloc.1
  IL_000e:  brtrue.s   IL_001d
  IL_0010:  nop
  IL_0011:  ldstr      "== Called"
  IL_0016:  call       void [mscorlib]System.Console::WriteLine(string)
  IL_001b:  nop
  IL_001c:  nop
  IL_001d:  ldloc.0
  IL_001e:  box        ConsoleApplication1.MyEnum
  IL_0023:  ldc.i4.s   99
  IL_0025:  box        ConsoleApplication1.MyEnum
  IL_002a:  callvirt   instance bool [mscorlib]System.Object::Equals(object)
  IL_002f:  ldc.i4.0
  IL_0030:  ceq
  IL_0032:  stloc.1
  IL_0033:  ldloc.1
  IL_0034:  brtrue.s   IL_0043
  IL_0036:  nop
  IL_0037:  ldstr      "Equals called"
  IL_003c:  call       void [mscorlib]System.Console::WriteLine(string)
  IL_0041:  nop
  IL_0042:  nop
  IL_0043:  ret

As you can see == generates ceq instruction, Equals method performes boxing and callvirt

Answer 3

There is a case that the other answers here have not mentioned that may help others.

With c# the underlying type of an enum is an integral. Because it is an integral, you can logically OR the enums together.

When using either of the above methods for equality will fail if enums are logically OR'd together.

So for some special cases, such as using enums as flags, you will need to logically AND the case you are testing for with first prior to checking for equality.

if ((enumInstance & MyEnum.SomeValue).Equals(MyEnum.SomeValue))

or

if ((enumInstance & MyEnum.SomeValue) == MyEnum.SomeValue)

Strictly speaking it's safest to use "==" with enums.

A complete list of possible enum types can be found here: https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/enum

Answer 4

As an extension to Jon Skeet's old answer, it is true that you get a compilation error when you compare Enum == YourActualEnum.Value , however when you do Enum == Enum , which compiles fine, it return false all the time.

public class TestClass
{
    public bool TestMethod1()
    {
        bool Result = false;

        Enum l_Value = TEST_ENUM.TEST_VALUE_1;

        Enum l_Check_Value = TEST_ENUM.TEST_VALUE_1;

        Result = l_Value == l_Check_Value;

        return Result;
    }

    public bool TestMethod2()
    {
        bool Result = false;

        TEST_ENUM l_Value = TEST_ENUM.TEST_VALUE_1;

        TEST_ENUM l_Check_Value = TEST_ENUM.TEST_VALUE_1;

        Result = l_Value == l_Check_Value;

        return Result;
    }

    public bool TestMethod3()
    {
        bool Result = false;

        Enum l_Value = TEST_ENUM.TEST_VALUE_1;

        Enum l_Check_Value = TEST_ENUM.TEST_VALUE_1;

        Result = l_Value.Equals(l_Check_Value);

        return Result;
    }

    public enum TEST_ENUM
    {
        TEST_VALUE_1,
        TEST_VALUE_2,
        TEST_VALUE_3
    }
}

if you try the following on a test app you'll get the following

Console.WriteLine("Method 1 result: {0}", myClass.TestMethod1());

Console.WriteLine("Method 2 result: {0}", myClass.TestMethod2());

Console.WriteLine("Method 3 result: {0}", myClass.TestMethod3());

you will get the following results

Method 1 result: False Method 2 result: True Method 3 result: True

If you wonder why would you ever compare Enum against Enum....I discovered it while trying to be smart while creating an EnumConverter and a FlagConvert for a WPF project. There you receive only an object value as parameter and for the flag converter specifically i wanted to provide a special text for when no flag was selected (ie the enum has a value of 0 which has no static member for it).

Nothing else worked (including value.Equals(0), value.Equals((int)0) ) except this:

l_Source_Type = value.GetType();

if (l_Source_Type.IsDefined(typeof(FlagsAttribute)))
{
    Enum l_Value = (Enum)value;

    Enum l_Check_Value = (Enum)Enum.ToObject(l_Source_Type, 0);

    if (l_Value.Equals(l_Check_Value))
    {
        return String.Empty;
    }
}