An enum variable, anyone know if it is always defaulting to the first element?
3 Answers
It is whatever member of the enumeration represents the value 0. Specifically, from the documentation:
The default value of an
enum Eis the value produced by the expression(E)0.
As an example, take the following enum:
enum E
{
Foo, Bar, Baz, Quux
}
Without overriding the default values, printing default(E) returns Foo since it's the first-occurring element.
However, it is not always the case that 0 of an enum is represented by the first member. For example, if you do this:
enum F
{
// Give each element a custom value
Foo = 1, Bar = 2, Baz = 3, Quux = 0
}
Printing default(F) will give you Quux, not Foo.
If none of the elements in an enum G correspond to 0:
enum G
{
Foo = 1, Bar = 2, Baz = 3, Quux = 4
}
default(G) returns literally 0, although its type remains as G (as quoted by the docs above, a cast to the given enum type).
I think it's quite dangerous to rely on the order of the values in a enum and to assume that the first is always the default. This would be good practice if you are concerned about protecting the default value.
enum E
{
Foo = 0, Bar, Baz, Quux
}
Otherwise, all it takes is a careless refactor of the order and you've got a completely different default.
You can use this snippet :-D
using System;
using System.Reflection;
public static class EnumUtils
{
public static T GetDefaultValue<T>()
where T : struct, Enum
{
return (T)GetDefaultValue(typeof(T));
}
public static object GetDefaultValue(Type enumType)
{
var attribute = enumType.GetCustomAttribute<DefaultValueAttribute>(inherit: false);
if (attribute != null)
return attribute.Value;
var innerType = enumType.GetEnumUnderlyingType();
var zero = Activator.CreateInstance(innerType);
if (enumType.IsEnumDefined(zero))
return zero;
var values = enumType.GetEnumValues();
return values.GetValue(0);
}
}
Example:
using System;
public enum Enum1
{
Foo,
Bar,
Baz,
Quux
}
public enum Enum2
{
Foo = 1,
Bar = 2,
Baz = 3,
Quux = 0
}
public enum Enum3
{
Foo = 1,
Bar = 2,
Baz = 3,
Quux = 4
}
[DefaultValue(Enum4.Bar)]
public enum Enum4
{
Foo = 1,
Bar = 2,
Baz = 3,
Quux = 4
}
public static class Program
{
public static void Main()
{
var defaultValue1 = EnumUtils.GetDefaultValue<Enum1>();
Console.WriteLine(defaultValue1); // Foo
var defaultValue2 = EnumUtils.GetDefaultValue<Enum2>();
Console.WriteLine(defaultValue2); // Quux
var defaultValue3 = EnumUtils.GetDefaultValue<Enum3>();
Console.WriteLine(defaultValue3); // Foo
var defaultValue4 = EnumUtils.GetDefaultValue<Enum4>();
Console.WriteLine(defaultValue4); // Bar
}
}
