C Dynamic runtime cast

Question

I would like to implement a method with the following signature  dynamic Cast object obj  Type castTo     Anyone know how to do that  obj definitely implements castTo but needs to be cast properly in order to have some of my app s runtime binding stuff work out   Edit  If some of the answers don t make sense it s because I initially accidentally typed dynamic Cast dynamic obj  Type castTo   - I mean the input should be object or some other guaranteed base class

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Try a generic   public static T CastTo lt T gt  this dynamic obj  bool safeCast  where T class      try            return  T obj          catch            if safeCast  return null        else throw           This is in extension method format  so its usage would be as if it were a member of dynamic objects   dynamic myDynamic   new Something    var typedObject   myDynamic CastTo lt Something gt  false     EDIT  Grr  didn t see that  Yes  you could reflectively close the generic  and it wouldn t be hard to hide in a non-generic extension method   public static dynamic DynamicCastTo this dynamic obj  Type castTo  bool safeCast       MethodInfo castMethod   this GetType   GetMethod  CastTo   MakeGenericMethod castTo      return castMethod Invoke null  new object     obj  safeCast         I m just not sure what you d get out of this  Basically you re taking a dynamic  forcing a cast to a reflected type  then stuffing it back in a dynamic  Maybe you re right  I shouldn t ask  But  this ll probably do what you want  Basically when you go into dynamic-land  you lose the need to perform most casting operations as you can discover what an object is and does through reflective methods or trial and error  so there aren t many elegant ways to do this

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Best I got so far   dynamic DynamicCast object entity  Type to        var openCast   this GetType   GetMethod  Cast   BindingFlags Static   BindingFlags NonPublic       var closeCast   openCast MakeGenericMethod to       return closeCast Invoke entity  new     entity       static T Cast lt T gt  object entity  where T   class       return entity as T

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I realize this has been answered  but I used a different approach and thought it might be worth sharing  Also  I feel like my approach might produce unwanted overhead  However  I m not able to observer or calculate anything happening that is that bad under the loads we observe  I was looking for any useful feedback on this approach   The problem with working with dynamics is that you can t attach any functions to the dynamic object directly  You have to use something that can figure out the assignments that you don t want to figure out every time   When planning this simple solution  I looked at what the valid intermediaries are when attempting to retype similar objects  I found that a binary array  string  xml  json  or hard coding a conversion  IConvertable  were the usual approaches  I don t want to get into binary conversions due to a code maintainability factor and laziness   My theory was that Newtonsoft could do this by using a string intermediary   As a downside  I am fairly certain that when converting the string to an object  that it would use reflection by searching the current assembly for an object with matching properties  create the type  then instantiate the properties  which would require more reflection  If true  all of this can be considered avoidable overhead   C      This lives in a helper class public static ConvertDynamic lt T gt  dynamic data         return Newtonsoft Json JsonConvert DeserializeObject lt T gt  Newtonsoft Json JsonConvert SerializeObject data         Same helper  but in an extension class  public static class     but could be in a base class also  public static ToModelList lt T gt  this List lt dynamic gt  list        List lt T gt  retList   new List lt T gt         foreach dynamic d in list                retList Add ConvertDynamic lt T gt  d              With that said  this fits another utility I ve put together that lets me make any object into a dynamic  I know I had to use reflection to do that correctly   public static dynamic ToDynamic this object value        IDictionary lt string  object gt  expando   new ExpandoObject         foreach  PropertyDescriptor property in TypeDescriptor GetProperties value GetType             expando Add property Name  property GetValue value         return expando as ExpandoObject      I had to offer that function  An arbitrary object assigned to a dynamic typed variable cannot be converted to an IDictionary  and will break the ConvertDynamic function  For this function chain to be used it has to be provided a dynamic of System Dynamic ExpandoObject  or IDictionary lt string  object gt

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The opensource framework Dynamitey has a static method that does late binding using DLR including cast conversion among others   dynamic Cast object obj  Type castTo       return Dynamic InvokeConvert obj  castTo  explict true       The advantage of this over a Cast lt T gt  called using reflection  is that this will also work for any IDynamicMetaObjectProvider that has dynamic conversion operators  ie  TryConvert on DynamicObject

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Slight modification on  JRodd version to support objects coming from Json  JObject  public static dynamic ToDynamic this object value                IDictionary lt string  object gt  expando   new ExpandoObject               Get the type of object          Type t   value GetType               If is Dynamic Expando object         if  t Equals typeof ExpandoObject                          foreach  PropertyDescriptor property in TypeDescriptor GetProperties value GetType                     expando Add property Name  property GetValue value                        If coming from Json object         else if  t Equals typeof JObject                          foreach  JProperty property in  JToken value                  expando Add property Name  property Value                     else   Try converting a regular object                       string str   JsonConvert SerializeObject value               ExpandoObject obj   JsonConvert DeserializeObject lt ExpandoObject gt  str                return obj                              return expando as ExpandoObject

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This should work   public static dynamic Cast dynamic obj  Type castTo        return Convert ChangeType obj  castTo       Edit  I ve written the following test code   var x    123   var y   Cast x  typeof int    var z   y   7  var w   Cast z  typeof string       w     130    It does resemble the kind of  typecasting  one finds in languages like PHP  JavaScript or Python  because it also converts the value to the desired type   I don t know if that s a good thing  but it certainly works     -

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You can use the expression pipeline to achieve this   public static Func lt object  object gt  Caster Type type         var inputObject   Expression Parameter typeof object        return Expression Lambda lt Func lt object object gt  gt  Expression Convert inputObject  type   inputPara  Compile        which you can invoke like  object objAsDesiredType   Caster desiredType  obj    Drawbacks  The compilation of this lambda is slower than nearly all other methods mentioned already Advantages  You can cache the lambda  then this should be actually the fastest method  it is identical to handwritten code at compile time

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Alternatively   public static T Cast lt T gt  this dynamic obj  where T class      return obj as T

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I think you re confusing the issues of casting and converting here      Casting  The act of changing the type of a reference which points to an object   Either moving up or down the object hierarchy or to an implemented interface Converting  Creating a new object from the original source object of a different type and accessing it through a reference to that type      It s often hard to know the difference between the 2 in C  because both of them use the same C  operator  the cast    In this situation you are almost certainly not looking for a cast operation   Casting a dynamic to another dynamic is essentially an identity conversion   It provides no value because you re just getting a dynamic reference back to the same underlying object   The resulting lookup would be no different    Instead what you appear to want in this scenario is a conversion   That is morphing the underlying object to a different type and accessing the resulting object in a dynamic fashion   The best API for this is Convert ChangeType   public static dynamic Convert dynamic source  Type dest      return Convert ChangeType source  dest       EDIT   The updated question has the following line       obj definitely implements castTo   If this is the case then the Cast method doesn t need to exist   The source object can simply be assigned to a dynamic reference   dynamic d   source    It sounds like what you re trying to accomplish is to see a particular interface or type in the hierarchy of source through a dynamic reference   That is simply not possible   The resulting dynamic reference will see the implementation object directly   It doesn t look through any particular type in the hierarchy of source   So the idea of casting to a different type in the hierarchy and then back to dynamic is exactly identical to just assigning to dynamic in the first place   It will still point to the same underlying object

[c#] C#: Dynamic runtime cast

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