Creating a constant Dictionary in C

Question

What is the most efficient way to create a constant  never changes at runtime  mapping of strings to ints    I ve tried using a const Dictionary  but that didn t work out    I could implement a immutable wrapper with appropriate semantics  but that still doesn t seem totally right     For those who have asked  I m implementing IDataErrorInfo in a generated class and am looking for a way to make the columnName lookup into my array of descriptors    I wasn t aware  typo when testing  d oh   that switch accepts strings  so that s what I m gonna use  Thanks

User · Answer

I am not sure why no one mentioned this but in C# for things that I cannot assign const, I use static read-only properties.

Example:

public static readonly Dictionary<string, string[]> NewDictionary = new Dictionary<string, string[]>()
        {
            { "Reference1", Array1 },
            { "Reference2", Array2 },
            { "Reference3", Array3 },
            { "Reference4", Array4 },
            { "Reference5", Array5 }
        };

User · Answer

enum Constants       Abc   1      Def   2      Ghi   3         int i    int Enum Parse typeof Constants    Def

User · Answer

This is the closest thing you can get to a  CONST Dictionary    public static int GetValueByName string name        switch  name                case  bob   return 1          case  billy   return 2          default  return -1            The compiler will be smart enough to build the code as clean as possible

User · Answer

There does not seem to be any standard immutable interface for dictionaries  so creating a wrapper seems like the only reasonable option  unfortunately   Edit  Marc Gravell found the ILookup that I missed - that will allow you to at least avoid creating a new wrapper  although you still need to transform the Dictionary with  ToLookup     If this is a need constrained to a specific scenario  you might be better off with a more business-logic-oriented interface   interface IActiveUserCountProvider       int GetMaxForServer string serverName

User · Answer

If using 4 5  Framework I would use ReadOnlyDictionary  also ReadOnly Collection for lists  to do readonly mappings constants  It s implemented in the following way   static class SomeClass       static readonly ReadOnlyDictionary lt string int gt  SOME MAPPING            new ReadOnlyDictionary lt string int gt               new Dictionary lt string int gt                                     One   1                       Two   2

User · Answer

There are precious few immutable collections in the current framework  I can think of one relatively pain-free option in  NET 3 5   Use Enumerable ToLookup   - the Lookup lt   gt  class is immutable  but multi-valued on the rhs   you can do this from a Dictionary lt   gt  quite easily       Dictionary lt string  int gt  ids   new Dictionary lt string  int gt            abc  1     def  2     ghi  3             ILookup lt string  int gt  lookup   ids ToLookup x   gt  x Key  x   gt  x Value       int i   lookup  def   Single

User · Answer

enum Constants       Abc   1      Def   2      Ghi   3         int i    int Enum Parse typeof Constants    Def

User · Answer

enum Constants       Abc   1      Def   2      Ghi   3         int i    int Enum Parse typeof Constants    Def

User · Answer

Creating a truly compile-time generated constant dictionary in C  is not really a straightforward task  Actually  none of the answers here really achieve that   There is one solution though which meets your requirements  although not necessarily a nice one  remember that according to the C  specification  switch-case tables are compiled to constant hash jump tables  That is  they are constant dictionaries  not a series of if-else statements  So consider a switch-case statement like this   switch  myString       case  cat   return 0     case  dog   return 1     case  elephant   return 3      This is exactly what you want  And yes  I know  it s ugly

User · Answer

Why not   public class MyClass       private Dictionary lt string  int gt   myCollection   new Dictionary lt string  int gt         A   1       B   2       C   3           public IEnumerable lt KeyValuePair lt string int gt  gt  MyCollection               get   return  myCollection AsEnumerable lt KeyValuePair lt string  int gt  gt

User · Answer

There are precious few immutable collections in the current framework  I can think of one relatively pain-free option in  NET 3 5   Use Enumerable ToLookup   - the Lookup lt   gt  class is immutable  but multi-valued on the rhs   you can do this from a Dictionary lt   gt  quite easily       Dictionary lt string  int gt  ids   new Dictionary lt string  int gt            abc  1     def  2     ghi  3             ILookup lt string  int gt  lookup   ids ToLookup x   gt  x Key  x   gt  x Value       int i   lookup  def   Single

User · Answer

Why not use namespaces or classes to nest your values   It may be imperfect  but it is very clean   public static class ParentClass          here is the  dictionary  class     public static class FooDictionary               public const string Key1    somevalue           public const string Foobar    fubar             Now you can access  ParentClass FooDictionary Key1  etc

User · Answer

Creating a truly compile-time generated constant dictionary in C  is not really a straightforward task  Actually  none of the answers here really achieve that   There is one solution though which meets your requirements  although not necessarily a nice one  remember that according to the C  specification  switch-case tables are compiled to constant hash jump tables  That is  they are constant dictionaries  not a series of if-else statements  So consider a switch-case statement like this   switch  myString       case  cat   return 0     case  dog   return 1     case  elephant   return 3      This is exactly what you want  And yes  I know  it s ugly

User · Answer

Why not use namespaces or classes to nest your values   It may be imperfect  but it is very clean   public static class ParentClass          here is the  dictionary  class     public static class FooDictionary               public const string Key1    somevalue           public const string Foobar    fubar             Now you can access  ParentClass FooDictionary Key1  etc

User · Answer

There are precious few immutable collections in the current framework  I can think of one relatively pain-free option in  NET 3 5   Use Enumerable ToLookup   - the Lookup lt   gt  class is immutable  but multi-valued on the rhs   you can do this from a Dictionary lt   gt  quite easily       Dictionary lt string  int gt  ids   new Dictionary lt string  int gt            abc  1     def  2     ghi  3             ILookup lt string  int gt  lookup   ids ToLookup x   gt  x Key  x   gt  x Value       int i   lookup  def   Single

User · Answer

This is the closest thing you can get to a  CONST Dictionary    public static int GetValueByName string name        switch  name                case  bob   return 1          case  billy   return 2          default  return -1            The compiler will be smart enough to build the code as clean as possible

User · Answer

There are precious few immutable collections in the current framework  I can think of one relatively pain-free option in  NET 3 5   Use Enumerable ToLookup   - the Lookup lt   gt  class is immutable  but multi-valued on the rhs   you can do this from a Dictionary lt   gt  quite easily       Dictionary lt string  int gt  ids   new Dictionary lt string  int gt            abc  1     def  2     ghi  3             ILookup lt string  int gt  lookup   ids ToLookup x   gt  x Key  x   gt  x Value       int i   lookup  def   Single

User · Answer

There does not seem to be any standard immutable interface for dictionaries  so creating a wrapper seems like the only reasonable option  unfortunately   Edit  Marc Gravell found the ILookup that I missed - that will allow you to at least avoid creating a new wrapper  although you still need to transform the Dictionary with  ToLookup     If this is a need constrained to a specific scenario  you might be better off with a more business-logic-oriented interface   interface IActiveUserCountProvider       int GetMaxForServer string serverName

User · Answer

This is the closest thing you can get to a  CONST Dictionary    public static int GetValueByName string name        switch  name                case  bob   return 1          case  billy   return 2          default  return -1            The compiler will be smart enough to build the code as clean as possible

User · Answer

If using 4 5  Framework I would use ReadOnlyDictionary  also ReadOnly Collection for lists  to do readonly mappings constants  It s implemented in the following way   static class SomeClass       static readonly ReadOnlyDictionary lt string int gt  SOME MAPPING            new ReadOnlyDictionary lt string int gt               new Dictionary lt string int gt                                     One   1                       Two   2

User · Answer

Creating a truly compile-time generated constant dictionary in C  is not really a straightforward task  Actually  none of the answers here really achieve that   There is one solution though which meets your requirements  although not necessarily a nice one  remember that according to the C  specification  switch-case tables are compiled to constant hash jump tables  That is  they are constant dictionaries  not a series of if-else statements  So consider a switch-case statement like this   switch  myString       case  cat   return 0     case  dog   return 1     case  elephant   return 3      This is exactly what you want  And yes  I know  it s ugly

User · Answer

There does not seem to be any standard immutable interface for dictionaries  so creating a wrapper seems like the only reasonable option  unfortunately   Edit  Marc Gravell found the ILookup that I missed - that will allow you to at least avoid creating a new wrapper  although you still need to transform the Dictionary with  ToLookup     If this is a need constrained to a specific scenario  you might be better off with a more business-logic-oriented interface   interface IActiveUserCountProvider       int GetMaxForServer string serverName

User · Answer

There does not seem to be any standard immutable interface for dictionaries  so creating a wrapper seems like the only reasonable option  unfortunately   Edit  Marc Gravell found the ILookup that I missed - that will allow you to at least avoid creating a new wrapper  although you still need to transform the Dictionary with  ToLookup     If this is a need constrained to a specific scenario  you might be better off with a more business-logic-oriented interface   interface IActiveUserCountProvider       int GetMaxForServer string serverName

User · Answer

Just another idea since I am binding to a winforms combobox   public enum DateRange        Display Name    None        None   0       Display Name    Today        Today   1       Display Name    Tomorrow        Tomorrow   2       Display Name    Yesterday        Yesterday   3       Display Name    Last 7 Days        LastSeven   4       Display Name    Custom        Custom   99         int something    int DateRange None    To get the int value from the display name from   public static class EnumHelper lt T gt        public static T GetValueFromName string name                var type   typeof T           if   type IsEnum  throw new InvalidOperationException             foreach  var field in type GetFields                          var attribute   Attribute GetCustomAttribute field                  typeof DisplayAttribute   as DisplayAttribute              if  attribute    null                                if  attribute Name    name                                        return  T field GetValue null                                               else                               if  field Name    name                      return  T field GetValue null                                    throw new ArgumentOutOfRangeException  name              usage   var z    int EnumHelper lt DateRange gt  GetValueFromName  Last 7 Days

User · Answer

Creating a truly compile-time generated constant dictionary in C  is not really a straightforward task  Actually  none of the answers here really achieve that   There is one solution though which meets your requirements  although not necessarily a nice one  remember that according to the C  specification  switch-case tables are compiled to constant hash jump tables  That is  they are constant dictionaries  not a series of if-else statements  So consider a switch-case statement like this   switch  myString       case  cat   return 0     case  dog   return 1     case  elephant   return 3      This is exactly what you want  And yes  I know  it s ugly

User · Answer

This is the closest thing you can get to a  CONST Dictionary    public static int GetValueByName string name        switch  name                case  bob   return 1          case  billy   return 2          default  return -1            The compiler will be smart enough to build the code as clean as possible

User · Answer

I am not sure why no one mentioned this but in C# for things that I cannot assign const, I use static read-only properties.

Example:

public static readonly Dictionary<string, string[]> NewDictionary = new Dictionary<string, string[]>()
        {
            { "Reference1", Array1 },
            { "Reference2", Array2 },
            { "Reference3", Array3 },
            { "Reference4", Array4 },
            { "Reference5", Array5 }
        };

User · Answer

Just another idea since I am binding to a winforms combobox   public enum DateRange        Display Name    None        None   0       Display Name    Today        Today   1       Display Name    Tomorrow        Tomorrow   2       Display Name    Yesterday        Yesterday   3       Display Name    Last 7 Days        LastSeven   4       Display Name    Custom        Custom   99         int something    int DateRange None    To get the int value from the display name from   public static class EnumHelper lt T gt        public static T GetValueFromName string name                var type   typeof T           if   type IsEnum  throw new InvalidOperationException             foreach  var field in type GetFields                          var attribute   Attribute GetCustomAttribute field                  typeof DisplayAttribute   as DisplayAttribute              if  attribute    null                                if  attribute Name    name                                        return  T field GetValue null                                               else                               if  field Name    name                      return  T field GetValue null                                    throw new ArgumentOutOfRangeException  name              usage   var z    int EnumHelper lt DateRange gt  GetValueFromName  Last 7 Days

User · Answer

Why not   public class MyClass       private Dictionary lt string  int gt   myCollection   new Dictionary lt string  int gt         A   1       B   2       C   3           public IEnumerable lt KeyValuePair lt string int gt  gt  MyCollection               get   return  myCollection AsEnumerable lt KeyValuePair lt string  int gt  gt

User · Answer

enum Constants       Abc   1      Def   2      Ghi   3         int i    int Enum Parse typeof Constants    Def

[c#] Creating a constant Dictionary in C#

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