Down casting int to byte in generic class

Question

5.00/5 (2 votes)

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Say we have the following (simplified version part of a bigger code base to show the problem):

C#

public class someclass<T>
{
   public void somemethod(object obj)
   {
       T o = (T)obj;
   }
}

And we call the class as follows :

C#

public void main()
{
   someclass<byte> s = new someclass<byte>();
   
   s.somemethod(1); // passing an int (the compiler should be passing a byte but it's not)
}

We get an invalid cast error. How can this be resolved.

Posted 15-Apr-12 0:05am

Mehdi Gholam

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Comments

Nelek 15-Apr-12 7:06am

Interesting question. +5

Mehdi Gholam 15-Apr-12 7:31am

Came across this while debugging RaptorDB the doc version.

3 solutions

Solution 1

XML

someclass<byte> s = new someclass<byte>();

   s.somemethod(1);

conversion of Int to byte not feasible, due to size.

Explicit casting may work

Posted 15-Apr-12 0:52am

ersumitsahu

Updated 15-Apr-12 0:55am

v2

Comments

Mehdi Gholam 15-Apr-12 6:54am

This is not an answer.

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This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Mehdi Gholam · Accepted Answer · 2012-04-15T00:56:00

Solution 2

Found a solution as follows :

C#

...
   public void somemethod(object obj)
   {
            T o = default(T);
            if(typeof(T).Equals(obj.GetType()) == false )
            {
                o = (T) Convert.ChangeType(obj, typeof(T));
            }
            else
                o = (T)obj;
   }

Posted 15-Apr-12 0:56am

Mehdi Gholam

Comments

VJ Reddy 15-Apr-12 7:01am

Good answer. 5!

Mehdi Gholam 15-Apr-12 7:34am

Thanks VJ!

Espen Harlinn 15-Apr-12 18:39pm

5'ed!

Mehdi Gholam 16-Apr-12 0:52am

Thanks

OriginalGriff · Accepted Answer · 2012-04-15T01:04:00

Solution 3

Boxing - always fun with generics!
Try this:

C#

public class someclass<T>
    {
    public void somemethod(object obj)
        {
        T o = (T) Convert.ChangeType(obj, typeof(T));
        }
    }

Posted 15-Apr-12 1:04am

OriginalGriff

Comments

Nelek 15-Apr-12 7:06am

Elegant way. +5

Mehdi Gholam 15-Apr-12 7:10am

5'ed, I will have to check the performance difference of always converting vs checking the types beforehand.

OriginalGriff 15-Apr-12 7:22am

:laugh: - There were no answers when I started!
I'm only guessing but I suspect that since ChangeType is just a wrapper for the IConvertible method call, that it will be quicker to always convert - the type-to-same-type method is normally no-operation.
So I checked, and I'm way, way wrong: to check first is about twice as fast as not checking! 5 to you!

Mehdi Gholam 15-Apr-12 7:28am

Wow! you saved me the trouble, cheers :)

OriginalGriff 15-Apr-12 7:36am

Welcome!

someclass<byte> s = new someclass<byte>();
Stopwatch s1 = new Stopwatch();
s1.Start();
int v1 = 1;
for (int i = 0; i < 10000; i++)
{
s.somemethod(v1);
}
s1.Stop();
someclass2<byte> t = new someclass2<byte>();
byte v2 = 1;
Stopwatch s2 = new Stopwatch();
s2.Start();
for (int i = 0; i < 10000; i++)
{
t.somemethod(v2);
}
s2.Stop();
Console.WriteLine("{0}:{1}", s1.ElapsedTicks, s2.ElapsedTicks);
}

public class someclass<t>
{
public void somemethod(object obj)
{
T o = (T)Convert.ChangeType(obj, typeof(T));
}
}
public class someclass2<t>
{
public void somemethod(object obj)
{
T o = default(T);
if (typeof(T).Equals(obj.GetType()) == false)
{
o = (T)Convert.ChangeType(obj, typeof(T));
}
else
o = (T)obj;
}
Results: 7800:4160

Espen Harlinn 15-Apr-12 18:39pm

5'ed!

Down casting int to byte in generic class

3 solutions

Solution 2

Solution 3

Solution 1

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Down casting int to byte in generic class

3 solutions

Solution 2

Solution 3

Solution 1

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