Logo Questions Linux Laravel Mysql Ubuntu Git Menu
 

C# generic casting exception

I have run into an odd casting issue while using generics. The following code will throw an InvalidCastException even though clearly an int can be cast to a double. Can anyone explain this behaviour and how to bypass it?

public class TestClass<T>
{
    public T Cast(object o)
    {
        return (T)o;
    }
}

public void Main()
{
    TestClass<double> w = new TestClass<double>();
    double x = w.Cast(10);
}

Edit:

Since I am in .net 4.0 land anyway I have changed it to use 'dynamic' instead of 'object' and everything works as expected. Appreciate all the spot-on and quick replies.

like image 746
Andrew Hanlon Avatar asked Mar 16 '11 12:03

Andrew Hanlon


People also ask

What C is used for?

C programming language is a machine-independent programming language that is mainly used to create many types of applications and operating systems such as Windows, and other complicated programs such as the Oracle database, Git, Python interpreter, and games and is considered a programming foundation in the process of ...

What is the full name of C?

In the real sense it has no meaning or full form. It was developed by Dennis Ritchie and Ken Thompson at AT&T bell Lab. First, they used to call it as B language then later they made some improvement into it and renamed it as C and its superscript as C++ which was invented by Dr.

Is C language easy?

C is a general-purpose language that most programmers learn before moving on to more complex languages. From Unix and Windows to Tic Tac Toe and Photoshop, several of the most commonly used applications today have been built on C. It is easy to learn because: A simple syntax with only 32 keywords.

Is C programming hard?

C is more difficult to learn than JavaScript, but it's a valuable skill to have because most programming languages are actually implemented in C. This is because C is a “machine-level” language. So learning it will teach you how a computer works and will actually make learning new languages in the future easier.


2 Answers

But an object can't be cast to a double. The o parameter takes an object, not an int.

For example, the following code fails with an InvalidCastException:

 object o = 1000;
 double x = (double)o;
like image 151
Cody Gray Avatar answered Sep 24 '22 12:09

Cody Gray


You can use TypeConverter to convert variables

        public class TestClass<T>
        {
            public T Cast(object o)
            {
                TypeConverter converter = TypeDescriptor.GetConverter(o);
                if (converter.CanConvertTo(typeof(T)))
                {
                   var result = converter.ConvertTo(o, typeof(T));
                   return (T)result;
                }

                throw new InvalidCastException(
                      string.Format("Cannot convert from {0} to {1}", o.GetType().Name, typeof(T).Name));
            }
        }
like image 34
Stecya Avatar answered Sep 24 '22 12:09

Stecya