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;
}
}
}