C# Discussion Boards - CodeProject

Cast Action<T> to Action<object> [modified]

31-Mar-11 0:38

GDavy wrote:
Does anyone have any ideas how I could accomplish that?

An ugly workaround, but you could consider putting them in a separate app and using IPC to communicate with the COM-component. Once the app seems to hang, you kill it Smile | :)

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Adriaan Davel30-Mar-11 20:36

30-Mar-11 20:36

After much painfull and brain numbing reading I still don't understand why its not possible to cast between Action<T> and Action<object>, can anyone please explain this in small words (I currently have the brain of a 5 year old).

There was a poem written along time ago by a person dying with lots of pain, he called it 'Brother Pain', I'm about to write a poem called 'Brother Cannot implicitly convert type 'System.Action<T>' to 'System.Action<object>''

An example:

public class Base
{
   public Func<object> OnComplete {get;set;}
   public Base(Func<object> onComplete)
   {
      OnComplete = onComplete;
   }
}
public class GenericBase<T> : Base
{
   public GenericBase(Func<T> onComplete) : base(onComplete) //Error
   {
      OnComplete = onComplete; //Error
   }
}

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modified on Thursday, March 31, 2011 3:22 AM

Groulien30-Mar-11 22:01

Groulien

30-Mar-11 22:01

It says 'implicitly', so have you tried an explicit cast?

public class GenericBase<T> : Base
{
  public GenericBase(Func<T> onComplete) : base((Func<object>)onComplete) //Added an explicit cast
  {
    OnComplete = (Func<object>)onComplete; //I'm not sure but I believe this is already done by 'base(onComplete)' constructor
  }
}

Adriaan Davel30-Mar-11 22:37

30-Mar-11 22:37

Did it build on your side? On my side I get 'Cannot convert type 'System.Func<T>' to 'System.Func<object>''

At least now my build error message is different Smile | :)

____________________________________________________________
Be brave little warrior, be VERY brave

Eddy Vluggen30-Mar-11 22:06

30-Mar-11 22:06

Adriaan Davel wrote:
After much painfull and brain numbing reading I still don't understand why its not possible to cast between Action<T> and Action<object>,

Because T might be an integer, and that's not compatible with object.

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Adriaan Davel30-Mar-11 22:32

30-Mar-11 22:32

Not sure I understand what you mean, this object x = 1; works...

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Wayne Gaylard30-Mar-11 22:37

Wayne Gaylard

30-Mar-11 22:37

Your example would still be an object, allocated on the heap. To use x as an integer would still need to be converted (int)x = ?

Eddy Vluggen30-Mar-11 22:44

30-Mar-11 22:44

Adriaan Davel wrote:
this object x = 1; works

That wraps your value-type with a reference-type; your number is actually stored in the object, but a number is not an object itself.

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Adriaan Davel30-Mar-11 22:49

30-Mar-11 22:49

Ok, but in non-generic syntax this works:

private void Button_Click(object sender, RoutedEventArgs e)
{
    Calc(1);
}

private void Calc(object val)
{

}

but in generic syntax it doesn't?

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Eddy Vluggen30-Mar-11 22:55

30-Mar-11 22:55

"Shouldn't"; there's a difference between simple types (anything that's a value) and classes, that's why there's a "where T:class" constraint Smile | :)

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Adriaan Davel30-Mar-11 23:02

30-Mar-11 23:02

I know that, and object allows me to pass either and respond accordingly inside the method to which I passed the parameter

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Eddy Vluggen30-Mar-11 23:19

30-Mar-11 23:19

..because you can check what type of object that it is. That's what VS does at compile-time, and since an integer isn't an object it gives an error. It could be wrapped in an object, that's true - but if that's what should be done, then it has to be explicit. Remember that you can't inherit from an integer, so it does make sense to differentiate between the parameter-behaviour and the generics' behaviour Smile | :)

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