A generic list of anonymous class

Question

In C  3 0 you can create anonymous class with the following syntax  var o   new   Id   1  Name    Foo       Is there a way to add these anonymous class to a generic list   Example   var o   new   Id   1  Name    Foo     var o1   new   Id   2  Name    Bar      List lt var gt  list   new List lt var gt     list Add o   list Add o1     Another Example   List lt var gt  list   new List lt var gt      while                       list Add new  Id   x  Name   y

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You can do it this way   var o   new   Id   1  Name    Foo     var o1   new   Id   2  Name    Bar      var array   new     o  o1    var list   array ToList     list Add new   Id   3  Name    Yeah        It seems a little  hacky  to me  but it works - if you really need to have a list and can t just use the anonymous array

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You can do this in your code   var list   new     new   Id   1  Name    Foo      ToList    list Add new   Id   2  Name    Bar

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I checked the IL on several answers   This code efficiently provides an empty List       using System Linq              var list   new   new Id   default int   Name   default string    Skip 1  ToList

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You can create a list of dynamic   List lt dynamic gt  anons new List lt dynamic gt     foreach  Model model in models       var anon  new            Id   model Id        Name model Name          anons Add anon        dynamic  gets initialized by the first value added

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Try with this     var result   new List lt object gt      foreach  var test in model ToList         result Add new  Id   test IdSoc Nom   test Nom

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I usually use the following  mainly because you then  start  with a list that s empty   var list   Enumerable Range 0  0  Select e   gt  new   ID   1  Name        ToList    list Add new  ID   753159  Name    Lamont Cranston        etc    Lately  I ve been writing it like this instead   var list   Enumerable Repeat new   ID   1  Name         0  ToList    list Add new  ID   753159  Name    Lamont Cranston        Using the repeat method would also allow you to do   var myObj   new   ID   1  Name    John     var list   Enumerable Repeat myObj  1  ToList    list Add new   ID   2  Name    Liana          which gives you the initial list with the first item already added

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Instead of this   var o   new   Id   1  Name    Foo      var o1   new   Id   2  Name    Bar       List  lt var gt  list   new List lt var gt      list Add o    list Add o1     You could do this   var o   new   Id   1  Name    Foo      var o1   new   Id   2  Name    Bar       List lt object gt  list   new List lt object gt      list Add o    list Add o1     However  you will get a compiletime error if you try to do something like this in another scope  although it works at runtime   private List lt object gt  GetList          List lt object gt  list   new List lt object gt         var o   new   Id   1  Name    Foo          var o1   new   Id   2  Name    Bar          list Add o        list Add o1       return list     private void WriteList         foreach  var item in GetList                    Console WriteLine  Name  0  1    item Name  Environment NewLine              The problem is that only the members of Object are available at runtime  although intellisense will show the properties id and name   In  net 4 0 a solution is to use the keyword dynamic istead of object in the code above   Another solution is to use reflection to get the properties  using System  using System Collections Generic  using System Reflection   namespace ConsoleApplication1       class Program               static void Main string   args                        Program p   new Program                var anonymous   p GetList new                    new   Id   1  Name    Foo                            new   Id   2  Name    Bar                                 p WriteList anonymous                      private List lt T gt  GetList lt T gt  params T   elements                        var a   TypeGenerator elements               return a                     public static List lt T gt  TypeGenerator lt T gt  T   at                        return new List lt T gt  at                      private void WriteList lt T gt  List lt T gt  elements                        PropertyInfo   pi   typeof T  GetProperties                foreach  var el in elements                                foreach  var p in pi                                        Console WriteLine   0    p GetValue el  null                                                Console ReadLine

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I guess  List lt T gt  CreateEmptyGenericList lt T gt  T example        return new List lt T gt        void something         var o   new   Id   1  Name    foo         var emptyListOfAnonymousType   CreateEmptyGenericList o       will work   You might also consider writing it like this   void something         var String   string Emtpy      var Integer   int MinValue      var emptyListOfAnonymousType   CreateEmptyGenericList new   Id   Integer  Name   String

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Here is a another method of creating a List of anonymous types that allows you to start with an empty list  but still have access to IntelliSense   var items      Select  t   gt  new  Id   1  Name    foo     ToList      If you wanted to keep the first item  just put one letter in the string   var items    1  Select  t   gt  new  Id   1  Name    foo     ToList

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For your second example  where you have to initialize a new List lt T gt   one idea is to create an anonymous list  and then clear it   var list   new     o  o1   ToList    list Clear       and you can keep adding  while                       list Add new   Id   x  Name   y                  Or as an extension method  should be easier   public static List lt T gt  GetEmptyListOfThisType lt T gt  this T item        return new List lt T gt          so you can call  var list   new   Id   0  Name        GetEmptyListOfThisType      Or probably even shorter   var list   new int 0  Select x   gt  new   Id   0  Name         Tolist

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var list   new    new  FirstField   default string   SecondField   default int   ThirdField   default double      ToList    list RemoveAt 0

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Deriving from this answer  I came up with two methods that could do the task            lt summary gt          Create a list of the given anonymous class   lt paramref name  definition   gt  isn t called  it is only used         for the needed type inference  This overload is for when you don t have an instance of the anon class         and don t want to make one to make the list           lt  summary gt           lt typeparam name  T  gt  lt  typeparam gt           lt param name  definition  gt  lt  param gt           lt returns gt  lt  returns gt   pragma warning disable RECS0154    Parameter is never used     public static List lt T gt  CreateListOfAnonType lt T gt  Func lt T gt  definition   pragma warning restore RECS0154    Parameter is never used               return new List lt T gt                    lt summary gt          Create a list of the given anonymous class   lt paramref name  definition   gt  isn t added to the list  it is         only used for the needed type inference  This overload is for when you do have an instance of the anon         class and don t want the compiler to waste time making a temp class to define the type           lt  summary gt           lt typeparam name  T  gt  lt  typeparam gt           lt param name  definition  gt  lt  param gt           lt returns gt  lt  returns gt   pragma warning disable RECS0154    Parameter is never used     public static List lt T gt  CreateListOfAnonType lt T gt  T definition   pragma warning restore RECS0154    Parameter is never used               return new List lt T gt             You can use the methods like  var emptyList   CreateListOfAnonType     gt new   Id   default int   Name   default string        or var existingAnonInstance   new   Id   59  Name    Joe     var otherEmptyList   CreateListOfAnonType existingAnonInstance     This answer has a similar idea  but I didn t see it until after I made those methods

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static void Main         List lt int gt  list   new List lt int gt         list Add 2       list Add 3       list Add 5       list Add 7

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You could do   var list   new     o  o1   ToList      There are lots of ways of skinning this cat  but basically they ll all use type inference somewhere - which means you ve got to be calling a generic method  possibly as an extension method   Another example might be   public static List lt T gt  CreateList lt T gt  params T   elements         return new List lt T gt  elements      var list   CreateList o  o1     You get the idea

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Here is the answer   string result   String Empty   var list   new          new   Number   10  Name    Smith         new   Number   10  Name    John       ToList     foreach  var item in list        result    String Format  Name  0   Number  1  n   item Name  item Number      MessageBox Show result

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There are many ways to do this  but some of the responses here are creating a list that contains garbage elements  which requires you to clear the list      If you are looking for an empty list of the generic type  use a Select against a List of Tuples to make the empty list    No elements will be instantiated   Here s the one-liner to create an empty list    var emptyList   new List lt Tuple lt int  string gt  gt               Select t   gt  new   Id   t Item1  Name   t Item2    ToList      Then you can add to it using your generic type    emptyList Add new   Id   1  Name    foo       emptyList Add new   Id   2  Name    bar        As an alternative  you can do something like below to create the empty list  But  I prefer the first example because you can use it for a populated collection of Tuples as well      var emptyList   new List lt object gt               Select t   gt  new   Id   default int   Name   default string     ToList

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Here is my attempt   List lt object gt  list   new List lt object gt    new   Id   10  Name    Testing1     new  Id  2  Name   Testing2         I came up with this when I wrote something similar for making a Anonymous List for a custom type

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Not exactly  but you can say List lt object gt  and things will work  However  list 0  Id won t work    This will work at runtime in C  4 0 by having a List lt dynamic gt   that is you won t get IntelliSense

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This is an old question  but I thought I d put in my C  6 answer  I often have to set up test data that is easily entered in-code as a list of tuples  With a couple of extension functions  it is possible to have this nice  compact format  without repeating the names on each entry   var people  new List lt Tuple lt int  int  string gt  gt           1  11   Adam         2  22   Bill         3  33   Carol     Select t   gt  new   Id   t Item1  Age   t Item2  Name   t Item3       This gives an IEnumerable - if you want a list that you can add to then just add ToList     The magic comes from custom extension Add methods for tuples  as described at https   stackoverflow com a 27455822 4536527   public static class TupleListExtensions          public static void Add lt T1  T2 gt  this IList lt Tuple lt T1  T2 gt  gt  list              T1 item1  T2 item2                  list Add Tuple Create item1  item2               public static void Add lt T1  T2  T3 gt  this IList lt Tuple lt T1  T2  T3 gt  gt  list              T1 item1  T2 item2  T3 item3            list Add Tuple Create item1  item2  item3              and so on         The only thing I don t like is that the types are separated from the names  but if you really don t want to make a new class then this approach will still let you have readable data

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If you are using C  7 or above  you can use tuple types instead of anonymous types   var myList   new List lt  int IntProp  string StrProp  gt     myList Add  IntProp  123  StrProp   XYZ

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In latest version 4 0  can use dynamic like below  var list   new List lt dynamic gt             list Add new               Name    Damith                  foreach var item in list               Console WriteLine item Name

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I m very surprised nobody has suggested collection initializers  This way can only add objects when the list is created hence the name however it seems like the nicest way of doing it  No need to create an array then convert it to a list   var list   new List lt dynamic gt            new   Id   1  Name    Foo          new   Id   2  Name    Bar          You can always use object instead of dynamic but trying to keep it in a true generic way then dynamic makes more sense

[c#] A generic list of anonymous class

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