Parameterized type
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Thread: Parameterized type

  1. #1
    Join Date
    Feb 2009
    Posts
    2

    Parameterized type

    A would be a C++ legitimate template doesn't work in C#:

    public void PassDoubleArrayToList<T>( double [] x, List<T> items ) where T : struct
    {
    for( int i = 0; i < x.Count(); ++i )
    {
    items.Add( (T) x[i] );
    }
    }

    The compiler complains: error CS0030: Cannot convert type 'double' to 'T'. Is there any work around? I would like to use only numeric types with T: double, int, bool, etc. I have tried a lot of ideas, so a piece of code would be appreciated greatly.

  2. #2
    Join Date
    Jun 2008
    Posts
    2,477

    Re: Parameterized type

    A better way to do this would be:

    Code:
    List<double> myList = new List<double>(myDoubleArray);
    As for your question, you cannot specify double[] as the Array parameter because you need to fill a List<T>, which could be any struct type, so your array needs to be generic as well. The cast is also unnecessary.

    Code:
    private static void PopList<T>(T[] arry, List<T> list) where T : struct
    {
        for (int i = 0; i < arry.Length; ++i)
        {
            list.Add(arry[i]);
        }
    }
    However, T does not need to derive from struct as any object in an array of T can be added to a list of T (that is why there is a default constructor for doing this);
    Last edited by BigEd781; February 21st, 2009 at 04:30 PM.

  3. #3
    Join Date
    Feb 2009
    Posts
    2

    Re: Parameterized type

    Thank you for your reply. Unfortunately, you changed the problem. Indeed, I have to assign only array of doubles either to list of doubles, or integers (with rounding), or Booleans. This is the problem.

  4. #4
    Join Date
    Jun 2008
    Posts
    2,477

    Re: Parameterized type

    A boolean cannot be expressed as a number in C#. So this won't work:

    Code:
    if (0) {}
    C++ templates != C# Generics
    If you need to convert the array, I would look at the static Array.ConvertAll<T,T> method.
    I should note that I am no expert here, so someon more experienced than myself may have a better solution for you.
    Last edited by BigEd781; February 21st, 2009 at 09:42 PM.

  5. #5
    Join Date
    Mar 2008
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    IRAN
    Posts
    811

    Re: Parameterized type

    Generics are strict and they should be.

    assume that some one initialize T with something like Foo type that is a user defined class. then how do you expect that in run-time compiler cast double to Foo!
    Please rate my post if it was helpful for you.
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