Equivalent of typedef in C

Question

Is there a typedef equivalent in C   or someway to get some sort of similar behaviour  I ve done some googling  but everywhere I look seems to be negative  Currently I have a situation similar to the following   class GenericClass lt T gt         public event EventHandler lt EventData gt  MyEvent      public class EventData   EventArgs      snip                 snip     Now  it doesn t take a rocket scientist to figure out that this can very quickly lead to a lot of typing  apologies for the horrible pun  when trying to implement a handler for that event  It d end up being something like this   GenericClass lt int gt  gcInt   new GenericClass lt int gt   gcInt MyEvent    new EventHandler lt GenericClass lt int gt  EventData gt  gcInt MyEvent           private void gcInt MyEvent object sender  GenericClass lt int gt  EventData e        throw new NotImplementedException        Except  in my case  I was already using a complex type  not just an int  It d be nice if it were possible to simplify this a little     Edit  ie  perhaps typedefing the EventHandler instead of needing to redefine it to get similar behaviour

User · Answer

You can use an open source library and NuGet package called LikeType that I created that will give you the GenericClass<int> behavior that you're looking for.

The code would look like:

public class SomeInt : LikeType<int>
{
    public SomeInt(int value) : base(value) { }
}

[TestClass]
public class HashSetExample
{
    [TestMethod]
    public void Contains_WhenInstanceAdded_ReturnsTrueWhenTestedWithDifferentInstanceHavingSameValue()
    {
        var myInt = new SomeInt(42);
        var myIntCopy = new SomeInt(42);
        var otherInt = new SomeInt(4111);

        Assert.IsTrue(myInt == myIntCopy);
        Assert.IsFalse(myInt.Equals(otherInt));

        var mySet = new HashSet<SomeInt>();
        mySet.Add(myInt);

        Assert.IsTrue(mySet.Contains(myIntCopy));
    }
}

User · Answer

Both C   and C  are missing easy ways to create a new type which is semantically identical to an exisiting type  I find such  typedefs  totally essential for type-safe programming and its a real shame c  doesn t have them built-in  The difference between void f string connectionID  string username  to void f ConID connectionID  UserName username  is obvious       You can achieve something similar in C   with boost in BOOST STRONG TYPEDEF    It may be tempting to use inheritance but that has some major limitations    it will not work for primitive types the derived type can still be casted to the original type  ie we can send it to a function receiving our original type  this defeats the whole purpose we cannot derive from sealed classes  and ie many  NET classes are sealed     The only way to achieve a similar thing in C  is by composing our type in a new class   Class SomeType      public void Method             sealed Class SomeTypeTypeDef     public SomeTypeTypeDef SomeType composed    this Composed   composed       private SomeType Composed   get       public override string ToString     gt  Composed ToString      public override int GetHashCode     gt  HashCode Combine Composed     public override bool Equals object obj    gt  obj is TDerived o  amp  amp  Composed Equals o Composed      public bool Equals SomeTypeTypeDefo    gt  object Equals this  o         proxy the methods we want   public void Method     gt  Composed Method        While this will work it is very verbose for just a typedef  In addition we have a problem with serializing  ie to Json  as we want to serialize the class through its Composed property   Below is a helper class that uses the  Curiously Recurring Template Pattern  to make this much simpler   namespace Typedef       JsonConverter typeof JsonCompositionConverter      public abstract class Composer lt TDerived  T gt    IEquatable lt TDerived gt  where TDerived   Composer lt TDerived  T gt        protected Composer T composed    this Composed   composed        protected Composer TDerived d    this Composed   d Composed         protected T Composed   get         public override string ToString     gt  Composed ToString        public override int GetHashCode     gt  HashCode Combine Composed       public override bool Equals object obj    gt  obj is Composer lt TDerived  T gt  o  amp  amp  Composed Equals o Composed        public bool Equals TDerived o    gt  object Equals this  o          class JsonCompositionConverter   JsonConverter       static FieldInfo GetCompositorField Type t          var fields   t BaseType GetFields BindingFlags Instance   BindingFlags NonPublic   BindingFlags Public   BindingFlags FlattenHierarchy         if  fields Length  1  throw new JsonSerializationException          return fields 0              public override bool CanConvert Type t          var fields   t GetFields BindingFlags Instance   BindingFlags NonPublic   BindingFlags Public   BindingFlags FlattenHierarchy         return fields Length    1                assumes Compositor lt T gt  has either a constructor accepting T or an empty constructor     public override object ReadJson JsonReader reader  Type objectType  object existingValue  JsonSerializer serializer          while  reader TokenType    JsonToken Comment  amp  amp  reader Read               if  reader TokenType    JsonToken Null  return null         var compositorField   GetCompositorField objectType         var compositorType   compositorField FieldType        var compositorValue   serializer Deserialize reader  compositorType         var ctorT   objectType GetConstructor new Type     compositorType           if    ctorT is null   return Activator CreateInstance objectType  compositorValue         var ctorEmpty   objectType GetConstructor new Type               if  ctorEmpty is null  throw new JsonSerializationException          var res   Activator CreateInstance objectType         compositorField SetValue res  compositorValue         return res             public override void WriteJson JsonWriter writer  object o  JsonSerializer serializer          var compositorField   GetCompositorField o GetType           var value   compositorField GetValue o         serializer Serialize writer  value                  With Composer the above class becomes simply   sealed Class SomeTypeTypeDef   Composer lt SomeTypeTypeDef  SomeType gt       public SomeTypeTypeDef SomeType composed    base composed            proxy the methods we want    public void Method     gt  Composed Method        And in addition the SomeTypeTypeDef will serialize to Json in the same way that SomeType does   Hope this helps

User · Answer

For non-sealed classes simply inherit from them   public class Vector   List lt int gt        But for sealed classes it s possible to simulate typedef behavior with such base class   public abstract class Typedef lt T  TDerived gt  where TDerived   Typedef lt T  TDerived gt   new         private T  value       public static implicit operator T Typedef lt T  TDerived gt  t                return t    null   default   t  value             public static implicit operator Typedef lt T  TDerived gt  T t                return t    null   default   new TDerived    value   t                Usage examples  class CountryCode   Typedef lt string  CountryCode gt      class CurrencyCode   Typedef lt string  CurrencyCode gt      class Quantity   Typedef lt int  Quantity gt       void Main         var canadaCode    CountryCode  CA       var canadaCurrency    CurrencyCode  CAD       CountryCode cc   canadaCurrency            Compilation error     Concole WriteLine canadaCode     CA        true     Concole WriteLine canadaCurrency           CAD      var qty    Quantity 123      Concole WriteLine qty                      123

User · Answer

C  supports some inherited covariance for event delegates  so a method like this   void LowestCommonHander  object sender  EventArgs e              Can be used to subscribe to your event  no explicit cast required   gcInt MyEvent    LowestCommonHander    You can even use lambda syntax and the intellisense will all be done for you   gcInt MyEvent     sender  e    gt        e    you ll get correct intellisense here

User · Answer

No  there s no true equivalent of typedef  You can use  using  directives within one file  e g   using CustomerList   System Collections Generic List lt Customer gt     but that will only impact that source file  In C and C    my experience is that typedef is usually used within  h files which are included widely - so a single typedef can be used over a whole project  That ability does not exist in C   because there s no  include functionality in C  that would allow you to include the using directives from one file in another   Fortunately  the example you give does have a fix - implicit method group conversion  You can change your event subscription line to just   gcInt MyEvent    gcInt MyEvent

User · Answer

Here is the code for it  enjoy   I picked that up from the dotNetReference type the  using  statement inside the namespace line 106 http   referencesource microsoft com  mscorlib microsoft win32 win32native cs  using System  using System Collections Generic  namespace UsingStatement       using Typedeffed   System Int32      using TypeDeffed2   List lt string gt       class Program               static void Main string   args                    Typedeffed numericVal   5          Console WriteLine numericVal              TypeDeffed2 things   new TypeDeffed2    whatever

User · Answer

If you know what you re doing  you can define a class with implicit operators to convert between the alias class and the actual class   class TypedefString    Example with a string  typedef        private string Value           public static implicit operator string TypedefString ts                return   ts    null    null   ts Value             public static implicit operator TypedefString string val                return new TypedefString   Value   val              I don t actually endorse this and haven t ever used something like this  but this could probably work for some specific circumstances

User · Answer

Jon really gave a nice solution  I didn t know you could do that   At times what I resorted to was inheriting from the class and creating its constructors  E g   public class FooList   List lt Foo gt            Not the best solution  unless your assembly gets used by other people   but it works

User · Answer

The best alternative to typedef that I ve found in C  is using  For example  I can control float precision via compiler flags with this code    if REAL T IS DOUBLE using real t   System Double   else using real t   System Single   endif   Unfortunately  it requires that you place this at the top of every file where you use real t  There is currently no way to declare a global namespace type in C

User · Answer

I think there is no typedef  You could only define a specific delegate type instead of the generic one in the GenericClass  i e   public delegate GenericHandler EventHandler lt EventData gt    This would make it shorter  But what about the following suggestion   Use Visual Studio  This way  when you typed  gcInt MyEvent       it already provides the complete event handler signature from Intellisense  Press TAB and it s there  Accept the generated handler name or change it  and then press TAB again to auto-generate the handler stub

[c#] Equivalent of typedef in C#

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