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DirectCast very very difficoult question

Posted on 2012-03-31
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Last Modified: 2012-04-18
Hi ,

I need a particular request.

In my project there are more then 150/200 calls to DirectCast.

I see that in C# there is an equivalent, but use a very different sintax.

In short:

I like to create a function that emulate DirectCast with another name:


My_DirectCast that inside use direct cast. To explain better the concept, something like this:

//
Public Function My_DirectCast(Expression , Type) as Object

 return DirectCast(Expression , Type)

End Function
//

and IT is not easy do this, because the compiler do not accept Type.

But after this I need a way to emulate the some situation in C#

//
Object My_DirectCast(Expression , Type)) {

Return (Type)Exression;

}
//

and probably this is more difficoult then the previous.

I am aware that it is not easy but I hope is possible do this.

If is possible do this I don't need to replace MANUALLY 150/200 or more code rows but only one.

Please HELP ME !!!!!
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Question by:luca345
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LVL 44

Expert Comment

by:AndyAinscow
ID: 37790788
The following works - but really needs error trapping to in case the conversion fails.

       public T  foo<T>(Object obj)
        {
            return (T) Convert.ChangeType(obj, typeof(T));
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            int i = foo<int>(23.45);
            double d = foo<double>(3.14159);
        }
0
 

Author Comment

by:luca345
ID: 37790812
Hi AndyAinscow ,

Because I have a bit difficoult to understand C# can you try to do the some in VB.net ?

Thank you !!
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Expert Comment

by:AndyAinscow
ID: 37791022
I thought you wanted it in C# because you gave an example in VB but said C# uses different syntax
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LVL 44

Expert Comment

by:AndyAinscow
ID: 37791390
VB isn't my speciality.
I've done a quick bit of searching and found this:

   Public Shared Function CAnyType(Of T)(ByRef UTO As Object) As T
        Return CType(UTO, T)
    End Function

I think you call it with something like
d = CAnyType(of double)(3.14159)
i = CAnyType(of integer)(2.345)

CType should be similar to your DirectCast, I think this might work or at least get you started
0
 

Author Comment

by:luca345
ID: 37791791
Hi Andy ,

Not work, I have try a similar code but VB don't accepts the 2° parameter because is a Type and VB want a object or class.
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LVL 44

Expert Comment

by:AndyAinscow
ID: 37794680
Works perfectly here - see picture
0002.jpg
0
 

Author Comment

by:luca345
ID: 37796704
Hi Andy ,

Thank you for your code but the the problem is more hard.

Please see attach.

I need a function that accept the some arguments of the original directcast and return the some value.
directr-cast.png
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LVL 44

Expert Comment

by:AndyAinscow
ID: 37797249
I don't know how the developers that wrote the compiler do the work of transferring a type in the way it is done in DirectCast.

The way it usually is done is what I showed earlier and here again using DirectCast in the function.
How one can pass a generic Type into a function
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LVL 44

Expert Comment

by:AndyAinscow
ID: 37797375
There are always two (rather silly) other possibilities

1)
Function CastToDouble(1.23) as Double   and so on for int, string....

2)
Function Cast(obj, string) as object  which has a big switch statement to call the appropriate DirectCast based upon the string value
0
 

Author Comment

by:luca345
ID: 37797565
Hi ,

I explain better what I need:

I my project there are 100/150 calls  to DirectCast.

In my compiler I need to go to 'replace' and 'all'    'DirectCast' with 'MyDirectCast' .

In your code I can't do 'replace all' because the arguments are different:

1) Is different the order.
2) You have add 'of'.


In short I need a clone of DirectCast with identical arguments::

//

a = DirectCast(b , c)

a = CAnyType(b , c )

//

In this mode, what I replace  'DirectCast' with ' CAnyType' I don't need to change others.

I don't known if this is possible or not.
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LVL 44

Accepted Solution

by:
AndyAinscow earned 500 total points
ID: 37797618
I don't think you can do it that simply.
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Author Closing Comment

by:luca345
ID: 37860504
Very good !
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