What to do when bit mask (flags) enum gets too large

I see values from at least a handful of different enumerations in there...

My first thought was to approach the problem by splitting the permissions up in logical groups (RuleGroupPermissions, RulePermissions, LocationPermissions, ...), and then having a class (WebAgentPermissions) exposing a property for each permission enum type.

Since the permission values seem repetitive, you could probably get away with a single enum in the end:

[Flags]
public enum Permissions
{
    View = 1,
    Add = 2,
    Edit = 4,
    Delete = 8
}

And then have the WebAgentPermissions class expose a property for each area where permissions are to be set;

class WebAgentPermissions
{
    public Permissions RuleGroup { get; set; }
    public Permissions Rule { get; set; }
    public Permissions Location { get; set; }
    // and so on...
}

You can check BitArray class. Maybe you will use it in future.

Language documentation says:

http://msdn.microsoft.com/en-us/library/system.flagsattribute.aspx

"The underlying type is Int32 and so the maximum single bit flag is 1073741824 and obviously there are a total of 32 flags for each enum."

However... UPDATED:

Commenter is correct. Check out this:

http://msdn.microsoft.com/en-us/library/ms182147(VS.80).aspx

Int32 is only the DEFAULT datatype! In fact you can specify Int64.

public enum MyEnumType : Int64

...allowing up to 64 values. But that certainly seems to be the maximum, after that you're going to be looking at re-engineering. Without knowing too much about the rest of your solution, I can't say exactly what might suit. But an array (or hash-map) of privilege identifiers is probably the most natural approach.

This turned out to be a more common problem than I thought it would be, where I was representing CSS classes as flags types and there were more than 64 possibilities. I've taken all I learned from that process and turned it into a reusable pattern, albeit since it's a struct, it's a copy-and-paste type pattern.

This is the BigFlags "enumerated type". It uses either BigInteger from System.Numerics, or if there is no way you can reference that assembly, there is a fallback that uses BitArray by simply turning off the NUMERICS preprocessor directive.

It behaves remarkably like a Flags enum, even defining such things as HasFlag(...), GetNames(), GetValues(), TryParse(...), a TypeConverter, IConvertible, etc. Since it does define a TypeConverter and IConvertible, it's also suitable for storing in a data store, albeit always as a string or text data type.

You expose the "enum" values as public static readonly members. Combined enum values are exposed as get-only properties.

To use it, copy and paste the code, then do a search and replace on BigFlags with your struct name, then delete the enums in the TODO section and add your values.

Hope somebody finds it useful.

#define NUMERICS

using System;
using System.Collections;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.ComponentModel;
using System.Globalization;
using System.Linq;
#if NUMERICS
using System.Numerics;
#endif
using System.Reflection;
using System.Text;
using System.Threading.Tasks;


namespace Aim
{
    /// <summary>
    /// The BigFlags struct behaves like a Flags enumerated type.
    /// <para>
    /// Note that if this struct will be stored in some type of data
    /// store, it should be stored as a string type. There are two
    /// reasons for this:
    /// </para>
    /// <para>
    /// 1. Presumably, this pattern is being used because the number
    /// of values will exceed 64 (max positions in a long flags enum).
    /// Since this is so, there is in any case no numeric type which
    /// can store all the possible combinations of flags.
    /// </para>
    /// <para>
    /// 2. The "enum" values are assigned based on the order that the
    /// static public fields are defined. It is much safer to store
    /// these fields by name in case the fields are rearranged. This
    /// is particularly important if this represents a permission set!
    /// </para>
    /// </summary>
    [
    TypeConverter( typeof( BigFlagsConverter ) )
    ]
    public struct BigFlags : IEquatable<BigFlags>,
        IComparable<BigFlags>, IComparable, IConvertible
    {
        #region State...

        private static readonly List<FieldInfo> Fields;
        private static readonly List<BigFlags> FieldValues;
#if NUMERICS
        private static readonly bool ZeroInit = true;
        private BigInteger Value;

        /// <summary>
        /// Creates a value taking ZeroInit into consideration.
        /// </summary>
        /// <param name="index"></param>
        /// <returns></returns>
        private static BigInteger CreateValue( int index )
        {
            if( ZeroInit && index == 0 )
            {
                return 0;
            }
            int idx = ZeroInit ? index - 1 : index;

            return new BigInteger( 1 ) << idx;
        }
#else
        private BitArray Array;

        /// <summary>
        /// Lazy-initialized BitArray.
        /// </summary>
        private BitArray Bits
        {
            get
            {
                if( null == Array )
                {
                    Array = new BitArray( Fields.Count );
                }
                return Array;
            }
        }
#endif
        #endregion ...State

        #region Construction...

        /// <summary>
        /// Static constructor. Sets the static public fields.
        /// </summary>
        static BigFlags()
        {
            Fields = typeof( BigFlags ).GetFields(
                BindingFlags.Public | BindingFlags.Static ).ToList();
            FieldValues = new List<BigFlags>();
            for( int i = 0; i < Fields.Count; i++ )
            {
                var field = Fields[i];
                var fieldVal = new BigFlags();
#if NUMERICS
                fieldVal.Value = CreateValue( i );
#else
                fieldVal.Bits.Set( i, true );
#endif
                field.SetValue( null, fieldVal );
                FieldValues.Add( fieldVal );
            }
        }
        #endregion ...Construction

        #region Operators...

        /// <summary>
        /// OR operator. Or together BigFlags instances.
        /// </summary>
        /// <param name="lhs"></param>
        /// <param name="rhs"></param>
        /// <returns></returns>
        public static BigFlags operator |( BigFlags lhs, BigFlags rhs )
        {
            var result = new BigFlags();
#if NUMERICS
            result.Value = lhs.Value | rhs.Value;
#else
            // BitArray is modified in place - always copy!
            result.Array = new BitArray( lhs.Bits ).Or( rhs.Bits );
#endif

            return result;
        }

        /// <summary>
        /// AND operator. And together BigFlags instances.
        /// </summary>
        /// <param name="lhs"></param>
        /// <param name="rhs"></param>
        /// <returns></returns>
        public static BigFlags operator &( BigFlags lhs, BigFlags rhs )
        {
            var result = new BigFlags();
#if NUMERICS
            result.Value = lhs.Value & rhs.Value;
#else
            // BitArray is modified in place - always copy!
            result.Array = new BitArray( lhs.Bits ).And( rhs.Bits );
#endif

            return result;
        }

        /// <summary>
        /// XOR operator. Xor together BigFlags instances.
        /// </summary>
        /// <param name="lhs"></param>
        /// <param name="rhs"></param>
        /// <returns></returns>
        public static BigFlags operator ^( BigFlags lhs, BigFlags rhs )
        {
            var result = new BigFlags();
#if NUMERICS
            result.Value = lhs.Value ^ rhs.Value;
#else
            // BitArray is modified in place - always copy!
            result.Array = new BitArray( lhs.Bits ).Xor( rhs.Bits );
#endif

            return result;
        }

        /// <summary>
        /// Equality operator.
        /// </summary>
        /// <param name="lhs"></param>
        /// <param name="rhs"></param>
        /// <returns></returns>
        public static bool operator ==( BigFlags lhs, BigFlags rhs )
        {
            return lhs.Equals( rhs );
        }

        /// <summary>
        /// Inequality operator.
        /// </summary>
        /// <param name="lhs"></param>
        /// <param name="rhs"></param>
        /// <returns></returns>
        public static bool operator !=( BigFlags lhs, BigFlags rhs )
        {
            return !( lhs == rhs );
        }
        #endregion ...Operators

        #region System.Object Overrides...

        /// <summary>
        /// Overridden. Returns a comma-separated string.
        /// </summary>
        /// <returns></returns>
        public override string ToString()
        {
#if NUMERICS
            if( ZeroInit && Value == 0 )
            {
                return Fields[0].Name;
            }
#endif
            var names = new List<string>();
            for( int i = 0; i < Fields.Count; i++ )
            {
#if NUMERICS
                if( ZeroInit && i == 0 )
                    continue;

                var bi = CreateValue( i );
                if( ( Value & bi ) ==  bi )
                    names.Add( Fields[i].Name );
#else
                if( Bits[i] )
                    names.Add( Fields[i].Name );
#endif
            }

            return String.Join( ", ", names );
        }

        /// <summary>
        /// Overridden. Compares equality with another object.
        /// </summary>
        /// <param name="obj"></param>
        /// <returns></returns>
        public override bool Equals( object obj )
        {
            if( obj is BigFlags )
            {
                return Equals( (BigFlags)obj );
            }

            return false;
        }

        /// <summary>
        /// Overridden. Gets the hash code of the internal BitArray.
        /// </summary>
        /// <returns></returns>
        public override int GetHashCode()
        {
#if NUMERICS
            return Value.GetHashCode();
#else
            int hash = 17;
            for( int i = 0; i < Bits.Length; i++ )
            {
                if( Bits[i] )
                    hash ^= i;
            }

            return hash;
#endif
        }
        #endregion ...System.Object Overrides

        #region IEquatable<BigFlags> Members...

        /// <summary>
        /// Strongly-typed equality method.
        /// </summary>
        /// <param name="other"></param>
        /// <returns></returns>
        public bool Equals( BigFlags other )
        {
#if NUMERICS
            return Value == other.Value;
#else
            for( int i = 0; i < Bits.Length; i++ )
            {
                if( Bits[i] != other.Bits[i] )
                    return false;
            }

            return true;
#endif
        }
        #endregion ...IEquatable<BigFlags> Members

        #region IComparable<BigFlags> Members...

        /// <summary>
        /// Compares based on highest bit set. Instance with higher
        /// bit set is bigger.
        /// </summary>
        /// <param name="other"></param>
        /// <returns></returns>
        public int CompareTo( BigFlags other )
        {
#if NUMERICS
            return Value.CompareTo( other.Value );
#else
            for( int i = Bits.Length - 1; i >= 0; i-- )
            {
                bool thisVal = Bits[i];
                bool otherVal = other.Bits[i];
                if( thisVal && !otherVal )
                    return 1;
                else if( !thisVal && otherVal )
                    return -1;
            }

            return 0;
#endif
        }
        #endregion ...IComparable<BigFlags> Members

        #region IComparable Members...

        int IComparable.CompareTo( object obj )
        {
            if( obj is BigFlags )
            {
                return CompareTo( (BigFlags)obj );
            }

            return -1;
        }
        #endregion ...IComparable Members

        #region IConvertible Members...

        /// <summary>
        /// Returns TypeCode.Object.
        /// </summary>
        /// <returns></returns>
        public TypeCode GetTypeCode()
        {
            return TypeCode.Object;
        }

        bool IConvertible.ToBoolean( IFormatProvider provider )
        {
            throw new NotSupportedException();
        }

        byte IConvertible.ToByte( IFormatProvider provider )
        {
#if NUMERICS
            return Convert.ToByte( Value );
#else
            throw new NotSupportedException();
#endif
        }

        char IConvertible.ToChar( IFormatProvider provider )
        {
            throw new NotSupportedException();
        }

        DateTime IConvertible.ToDateTime( IFormatProvider provider )
        {
            throw new NotSupportedException();
        }

        decimal IConvertible.ToDecimal( IFormatProvider provider )
        {
#if NUMERICS
            return Convert.ToDecimal( Value );
#else
            throw new NotSupportedException();
#endif
        }

        double IConvertible.ToDouble( IFormatProvider provider )
        {
#if NUMERICS
            return Convert.ToDouble( Value );
#else
            throw new NotSupportedException();
#endif
        }

        short IConvertible.ToInt16( IFormatProvider provider )
        {
#if NUMERICS
            return Convert.ToInt16( Value );
#else
            throw new NotSupportedException();
#endif
        }

        int IConvertible.ToInt32( IFormatProvider provider )
        {
#if NUMERICS
            return Convert.ToInt32( Value );
#else
            throw new NotSupportedException();
#endif
        }

        long IConvertible.ToInt64( IFormatProvider provider )
        {
#if NUMERICS
            return Convert.ToInt64( Value );
#else
            throw new NotSupportedException();
#endif
        }

        sbyte IConvertible.ToSByte( IFormatProvider provider )
        {
#if NUMERICS
            return Convert.ToSByte( Value );
#else
            throw new NotSupportedException();
#endif
        }

        float IConvertible.ToSingle( IFormatProvider provider )
        {
#if NUMERICS
            return Convert.ToSingle( Value );
#else
            throw new NotSupportedException();
#endif
        }

        string IConvertible.ToString( IFormatProvider provider )
        {
            return ToString();
        }

        object IConvertible.ToType( Type conversionType, IFormatProvider provider )
        {
            var tc = TypeDescriptor.GetConverter( this );

            return tc.ConvertTo( this, conversionType );
        }

        ushort IConvertible.ToUInt16( IFormatProvider provider )
        {
#if NUMERICS
            return Convert.ToUInt16( Value );
#else
            throw new NotSupportedException();
#endif
        }

        uint IConvertible.ToUInt32( IFormatProvider provider )
        {
#if NUMERICS
            return Convert.ToUInt32( Value );
#else
            throw new NotSupportedException();
#endif
        }

        ulong IConvertible.ToUInt64( IFormatProvider provider )
        {
#if NUMERICS
            return Convert.ToUInt64( Value );
#else
            throw new NotSupportedException();
#endif
        }
        #endregion ...IConvertible Members

        #region Public Interface...

        /// <summary>
        /// Checks <paramref name="flags"/> to see if all the bits set in
        /// that flags are also set in this flags.
        /// </summary>
        /// <param name="flags"></param>
        /// <returns></returns>
        public bool HasFlag( BigFlags flags )
        {
            return ( this & flags ) == flags;
        }

        /// <summary>
        /// Gets the names of this BigFlags enumerated type.
        /// </summary>
        /// <returns></returns>
        public static string[] GetNames()
        {
            return Fields.Select( x => x.Name ).ToArray();
        }

        /// <summary>
        /// Gets all the values of this BigFlags enumerated type.
        /// </summary>
        /// <returns></returns>
        public static BigFlags[] GetValues()
        {
            return FieldValues.ToArray();
        }

        /// <summary>
        /// Standard TryParse pattern. Parses a BigFlags result from a string.
        /// </summary>
        /// <param name="s"></param>
        /// <param name="result"></param>
        /// <returns></returns>
        public static bool TryParse( string s, out BigFlags result )
        {
            result = new BigFlags();
            if( String.IsNullOrEmpty( s ) )
                return true;

            var fieldNames = s.Split( ',' );
            foreach( var f in fieldNames )
            {
                var field = Fields.FirstOrDefault( x =>
                    String.Equals( x.Name, f.Trim(),
                    StringComparison.OrdinalIgnoreCase ) );
                if( null == field )
                {
                    result = new BigFlags();
                    return false;
                }
#if NUMERICS
                int i = Fields.IndexOf( field );
                result.Value |= CreateValue( i );
#else
                result.Bits.Set( Fields.IndexOf( field ), true );
#endif
            }

            return true;
        }

        //
        // Expose "enums" as public static readonly fields.
        // TODO: Replace this section with your "enum" values.
        //
        public static readonly BigFlags None;
        public static readonly BigFlags FirstValue;
        public static readonly BigFlags ValueTwo;
        public static readonly BigFlags ValueThree;
        public static readonly BigFlags ValueFour;
        public static readonly BigFlags ValueFive;
        public static readonly BigFlags ValueSix;
        public static readonly BigFlags LastValue;

        /// <summary>
        /// Expose flagged combinations as get-only properties.
        /// </summary>
        public static BigFlags FirstLast
        {
            get
            {
                return BigFlags.FirstValue | BigFlags.LastValue;
            }
        }
        #endregion ...Public Interface
    }

    /// <summary>
    /// Converts objects to and from BigFlags instances.
    /// </summary>
    public class BigFlagsConverter : TypeConverter
    {
        /// <summary>
        /// Can convert to string only.
        /// </summary>
        /// <param name="context"></param>
        /// <param name="destinationType"></param>
        /// <returns></returns>
        public override bool CanConvertTo( ITypeDescriptorContext context,
            Type destinationType )
        {
            return destinationType == typeof( String );
        }

        /// <summary>
        /// Can convert from any object.
        /// </summary>
        /// <param name="context"></param>
        /// <param name="sourceType"></param>
        /// <returns></returns>
        public override bool CanConvertFrom( ITypeDescriptorContext context,
            Type sourceType )
        {
            return true;
        }

        /// <summary>
        /// Converts BigFlags to a string.
        /// </summary>
        /// <param name="context"></param>
        /// <param name="culture"></param>
        /// <param name="value"></param>
        /// <param name="destinationType"></param>
        /// <returns></returns>
        public override object ConvertTo( ITypeDescriptorContext context,
            CultureInfo culture, object value, Type destinationType )
        {
            if( value is BigFlags && CanConvertTo( destinationType ) )
                return value.ToString();

            return null;
        }

        /// <summary>
        /// Attempts to parse <paramref name="value"/> and create and
        /// return a new BigFlags instance.
        /// </summary>
        /// <param name="context"></param>
        /// <param name="culture"></param>
        /// <param name="value"></param>
        /// <returns></returns>
        public override object ConvertFrom( ITypeDescriptorContext context,
            CultureInfo culture, object value )
        {
            var s = Convert.ToString( value );
            BigFlags result;
            BigFlags.TryParse( s, out result );

            return result;
        }
    }
}