Need help on generic methods

Question

3.67/5 (2 votes)

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I have 2 methods which I'm planning to refactor into a single method

C#

IFactory _factory

// Method 1

TClass obj = (TClass )_factory.CreateA(param1);

// Method 2

HClass obj  = (HClass )__factory.CreateB(param2);

Now I want a generic method which will return me generic object

Below is the code which I tried,But in vain.Get typecast error

C#

T CreateInst<<T>>() 
{
    T _requestType;
        if(_requestType.GetType() == typeof(TClass ))
        {
             _requestType = (TClass)_factory.CreateA(param1)  ;
        }
        else if(_requestType.GetType() == typeof(HClass ))
        {
            _requestType = (HClass)_factory.CreateB(param1)  ;
        }

    return _requestType;
}

Posted 20-Aug-13 23:31pm

explorerC

Updated 21-Aug-13 0:04am

v6

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2 solutions

Solution 1

C#

T CreateInst<<T>>()
{
    T _requestType;
        if(_requestType is TClass)
        {
             _requestType = (TClass)_factory.CreateA(param1)  ;
        }
        else if(_requestType is HClass )
        {
            _requestType = (HClass)_factory.CreateB(param1)  ;
        }

    return _requestType;
}

Posted 21-Aug-13 0:26am

Yesudasan Moses

Comments

explorerC 21-Aug-13 8:01am

Hi Moses
Again getting compilation error.Are you missing a cast

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Shmuel Zang · Accepted Answer · 2013-08-21T00:58:00

Solution 2

That happens because your method tries to assign an object of type TClass or HClass to an object of type T. Since there are no constraints for T, T can be anything and, you cannot assign TClass or HClass to anything...

Maybe, you intended to write something like:

C#

T CreateInst<T>(object param1) where T : class
{
    T _requestType = null;

    if(typeof(T) == typeof(TClass))
    {
        _requestType = _factory.CreateA(param1) as T  ;
    }
    else if(typeof(T) == typeof(HClass))
    {
        _requestType = _factory.CreateB(param1) as T ;
    }
 
    return _requestType;
}

Posted 21-Aug-13 0:58am

Shmuel Zang

Comments

explorerC 21-Aug-13 8:32am

Hey it works!!!...Thanks for the input
Is it possible to hold this object in generic object and access its properties ??

Shmuel Zang 21-Aug-13 8:56am

It is possible if you have a type constraint for a type that contains those properties. Think about it, since this is a generic type, the compiler needs a way to be sure that the type has the properties (or anything you want to do with that type)...

explorerC 22-Aug-13 4:24am

Thanks very much for your inputs

explorerC 22-Aug-13 7:09am

Hi Shmuel,

Type constraint is there, But it doesn't allow add multiple class constraint.

T CreateInst<t>(object param1) where T : TClass,HClass

Shmuel Zang 24-Aug-13 15:04pm

That's because no .NET class can be derived from 2 classes (in your case TClass and HClass)...