Anyone know a good workaround for the lack of an enum generic constraint?
What I want to do is something like this: I have enums with combined flagged values.
public static class EnumExtension
{
public static bool IsSet<T>( this T input, T matchTo )
where T:enum //the constraint I want that doesn't exist in C#3
{
return (input & matchTo) != 0;
}
}
So then I could do:
MyEnum tester = MyEnum.FlagA | MyEnum.FlagB
if( tester.IsSet( MyEnum.FlagA ) )
//act on flag a
Unfortunately C#'s generic where constraints have no enum restriction, only class and struct. C# doesn't see enums as structs (even though they are value types) so I can't add extension types like this.
Anyone know a workaround?
EDIT: This is now live in version 0.0.0.2 of UnconstrainedMelody.
(As requested on my blog post about enum constraints. I've included the basic facts below for the sake of a standalone answer.)
The best solution is to wait for me to include it in UnconstrainedMelody1. This is a library which takes C# code with "fake" constraints such as
where T : struct, IEnumConstraint
and turns it into
where T : struct, System.Enum
via a postbuild step.
It shouldn't be too hard to write IsSet ... although catering for both Int64 -based and UInt64 -based flags could be the tricky part. (I smell some helper methods coming on, basically allowing me to treat any flags enum as if it had a base type of UInt64 .)
What would you want the behaviour to be if you called
tester.IsSet(MyFlags.A | MyFlags.C)
? Should it check that all the specified flags are set? That would be my expectation.
I'll try to do this on the way home tonight... I'm hoping to have a quick blitz on useful enum methods to get the library up to a usable standard quickly, then relax a bit.
EDIT: I'm not sure about IsSet as a name, by the way. Options:
Thoughts welcome. I'm sure it'll be a while before anything's set in stone anyway...
1 or submit it as a patch, of course...
Darren，如果这些类型是特定的枚举，那么这将起作用 - 对于一般的枚举工作，您必须将它们转换为整数（或更可能是uint）来执行布尔运算：
public static bool IsSet( this Enum input, Enum matchTo )
{
return ( Convert.ToUInt32( input ) & Convert.ToUInt32( matchTo ) ) != 0;
}
Actually, it is possible, with an ugly trick. However, it cannot be used for extension methods.
public abstract class Enums<Temp> where Temp : class {
public static TEnum Parse<TEnum>(string name) where TEnum : struct, Temp {
return (TEnum)Enum.Parse(typeof(TEnum), name);
}
}
public abstract class Enums : Enums<Enum> { }
Enums.IsSet<DateTimeKind>("Local")
If you want to, you can give Enums<Temp> a private constructor and a public nested abstract inherited class with Temp as Enum , to prevent inherited versions for non-enums.