How to implement a method, into interface, with parameter and returned value generic in C#

Question

I would like to implement a interface with generic input parameter and returned value in C#. At the moment I have defined a interface:

interface IResponseFormatter
{
    T formatResponseOptimizated<T>(T[] tagsValues);
}

after that I have tried to implement a concrete class:

public class FormatResponseInterpolatedData : IResponseFormatter

{
    ILog log = LogManager.GetLogger(typeof(HistorianPersistenceImpl));



    public Dictionary<string, List<object[]>> formatResponseOptimizated <Dictionary<string, List<object[]>>> (IHU_RETRIEVED_DATA_VALUES[] tagsValues)
    {
        log.Info("ENTER [formatResponseOptimizated] tagValues: " + tagsValues);
        Dictionary<string, List<object[]>> result = new Dictionary<string, List<object[]>>();

        // built data logic

        return result;
    }
}

I would like to understand what I'm wrong about and how I can to make this implementation type.

Answer 1

You are defining a generic method in a non-generic interface.

Move T from being formatResponseOptimizated type parameter to IResponseFormatter type parameter, and provide a specification in the implementing class:

interface IResponseFormatter<T> {
    // Follow C# naming conventions: method names start in an upper case letter
    T FormatResponseOptimizated(T[] tagsValues);
}
public class FormatResponseInterpolatedData
     : IResponseFormatter<Dictionary<string,List<object[]>>> {
    public Dictionary<string,List<object[]>> FormatResponseOptimizated(Dictionary<string,List<object[]>>[] tagsValues) {
        ...
    }
}

Note that with a single type parameter T the return type of FormatResponseOptimizated must match the type of array element that it takes as its parameter T[]. If the two should be different, parameterize your interface on two types, say, TArg for the argument and TRet for return.