[Mono-list] Enum problem

[Iain McCoy]

On Sat, 2004-10-16 at 13:17 +0200, Francis Brosnan Blázquez wrote:
> Hi.
> 
> Working with enumerations I've found an strange behaviour. If you
> compile the following source code and run it:
> 
> --
> using System;
> 
> public class EnumTest {
> 	
> 	public enum TipoCarga {
> 		Positivo = 1/3,
> 		Negativo = 1 + (1/3),
> 		Neutro   = 1,
> 	}
> 
> 	public static void Main () {
> 		TipoCarga carga;
> 
> 		carga = TipoCarga.Positivo;
> 		Console.WriteLine ("carga value is: {0}", carga);
> 
> 		carga = TipoCarga.Neutro;
> 		Console.WriteLine ("carga value is: {0}", carga);
> 
> 		carga = TipoCarga.Negativo;
> 		Console.WriteLine ("carga value is: {0}", carga);
> 	}
> }
> --
> 
> 
> You get the following output:
> carga value is: Positivo
> carga value is: Neutro
> carga value is: Neutro
> 
> That is, on every assignment which uses TipoCarga.Negativo doesn't work.
> I've been reading about how enumerations works and seens to be that you
> can only use values from byte, sbyte, short, ushort, int, uint, long, or
> ulong types but not float or double types which can hold values as 1/3
> and 1 + (1/3). 
> 
> The odd thing is that assignment for Positivo = 1/3 works perfectly. 
> 
> Maybe mcs mustn't allow someone to compile the previous source code?

I haven't got a windows machine to run csc on to double check, but I
suspect what you're seeing is the compiler automatically coercing all of
your enum values to ints. This means that 1/3 = 0, so 1 + 1/3 = 0 and
therefore TipoCarga.Neutro == TipoCarga.Negativo. Whether this is what
css does or not I have no idea, but according to the spec it seems to be
correct (section 14.3 of the C# language specification 1.2):
"If the declaration of the enum member has a constant-expression
initializer, the value of that constant expression, implicitly converted
to the underlying type of the enum, is the associated value of the enum
member"

-- 
Iain McCoy <iain@mccoy.id.au>