c# - Polymorphic object creation without IF condition -

i have abstract class this:

public abstract class records     {         public string type;         public string source;         public int value;          protected records(string type, string source, int value)         {             type = type;             source = source;             value = value;         } } 

i create many classes inheriting class, , filling type field value coming static class this:

public static class contenttypesstring     {         public static string documentnew { { return "document - new month"; }}          public static string headlinesnew { { return "headlines - new month"; }}         etc...       } 

i able create child classes without having test "if foo == "document" type = contenttypesstring.documentnew" or equivalent switch case (i have lot of cases)

is there design pattern suits needs?

edit : several people pointed out, should show how create instances.

     private delegate splistitemcollection query(spweb web, datetime startdate, datetime enddate);      private readonly query _queries;         #region constructors        public queryhandler(spweb web, datetime starttimeselecteddate, datetime endtimeselecteddate)           {             if (web == null) throw new argumentnullexception("web");              _web = web;             _starttimeselecteddate = starttimeselecteddate;             _endtimeselecteddate = endtimeselecteddate;             recordslist = new list<records>();              // query invocation list             _queries = numberpagepermonthquery.preparedquery;             _queries += numberdocumentspermonthquery.preparedquery;             _queries += numberheadlinespermonthquery.preparedquery;             _queries += numberleaderboxpermonthquery.preparedquery;             _queries += numbernewspermonthquery.preparedquery;             _queries += numberpagesmodifiedpermonthquery.preparedquery;             _queries += numberpicturespermonthquery.preparedquery;             _queries += numberteasingpermonthquery.preparedquery;         }          #endregion constructors          #region public methods          // nullreferenceexception ? c#6 : item?.foreach(item => {}); ?         /*** no c#6 compiler in vs2012... ***/         public void queries()         {             foreach (var del in _queries.getinvocationlist())             {                 var queryresult =                     (splistitemcollection) del.dynamicinvoke(_web, _starttimeselecteddate, _endtimeselecteddate);                  recordslist.add(new records(del.method.name, _web.title, queryresult.count));             }         } 

edit² : solution chose

  public list<iquery> querylist { get; } // no delegate anymore, , static classes became implementations of iquery interface.         #region constructors        public queryhandler(spweb web, datetime starttimeselecteddate, datetime endtimeselecteddate)           {             if (web == null) throw new argumentnullexception("web");              _web = web;             _starttimeselecteddate = starttimeselecteddate;             _endtimeselecteddate = endtimeselecteddate;             recordslist = new list<records>();              querylist = new list<iquery>             {                 new numberdocumentspermonthquery(),                 new numberheadlinespermonthquery(),                 new numberleaderboxpermonthquery(),                 new numbernewspermonthquery(),                 new numberpagepermonthquery(),                 new numberpagesmodifiedpermonthquery(),                 new numberpicturespermonthquery(),                 new numberteasingpermonthquery()             };          }          #endregion constructors          #region public methods          // nullreferenceexception ? c#6 : item?.foreach(item => {}); ?         /*** no c#6 compiler in vs2012... ***/           public void queries()         {             foreach (var query in querylist)             {                 var queryresult = query.preparedquery(_web, _starttimeselecteddate, _endtimeselecteddate);                 recordslist.add(query.createrecord(_web.title, queryresult.count));             }         } 

record class follow implementation suggested @dbraillon implementation of iquery interface added method :

public records createrecord(string source, int value)         {             return new modifiedpagespermonthrecord(source, value); //or child of record class.          } 

and voilà. thank help.

you want make collection of records, string code of object type, , parameters.

one of many way - use builder.

firstly need configurate builder:

        var builder = new recordbuilder()             .registerbuilder("document", (source, value) => new document(source, value))             .registerbuilder("headlines", (source, value) => new headlines(source, value)); 

here specify how build record code "document" , "headlines".

to build record call:

        builder.build("document", "source", 1); 

builder code can (here if know how build record of passed type , make it):

public class recordbuilder {     public records build(string code, string source, int value)     {         func<string, int, records> buildaction;          if (recordbuilders.trygetvalue(code, out buildaction))         {             return buildaction(source, value);         }          return null;     }      public recordbuilder registerbuilder(string code, func<string, int, records> buildaction)     {         recordbuilders.add(code, buildaction);         return this;     }      private dictionary<string, func<string, int, records>> recordbuilders = new dictionary<string, func<string, int, records>> (); }   public class document : records {     public document(string source, int value) : base(contenttypesstring.documentnew, source, value)     {     } }  public class headlines : records {     public headlines(string source, int value) : base(contenttypesstring.headlinesnew, source, value)     {     } }