CODEWITHSUNDEEP
c#unit-testingclassgenerics
Eric
Eric

Reputation: 589

Generic class can't match argument list

Trying to write my first generic class in C#:

public class HighScoreList<ScoreType>
    where ScoreType : System.IComparable<ScoreType>
{
    ...

    public HighScoreList(List<ScoreType> highScoreList)
    {
          ....
    }

    ...
}

I have run into problems writing unit tests for it. It can't for some reason match the constructor's argument list and gives me the error:

Error 7 The best overloaded method match for 'TDGLX.FileManagement.HighScoreList.HighScoreList(System.Collections.Generic.List)' has some invalid arguments C:\Users\eric\Documents\Visual Studio 2010\Projects\TDGLX\UnitTests\FileManagmentTest\HighScoreListTest.cs 183 54 UnitTests

On this and several other tests:

   HighScoreList<GenericScore> highScoreList =
        new HighScoreList<GenericScore>(new List<GenericScore>()
                {
                    new GenericScore("Person1",400),
                    new GenericScore("Person2",200),
                    new GenericScore("Person3",100)
                });

        HighScoreList<GenericScore> target =
            new HighScoreList<GenericScore>(highScoreList);

Here is the class that I'm using as a parameter to the template argument list in my tests.

[Serializable()]
public class GenericScore : System.IComparable<GenericScore>
{
    public GenericScore(string name,int score)
    {
        Name = name;
        Score = score;
    }

    public string Name { get; set; }
    public int Score { get; set; }

    public int CompareTo(GenericScore other)
    {
        return this.Score.CompareTo(other.Score);
    }
}

I really can't figure out what's wrong with the test. Is there something have misunderstood about C# generics?

Upvotes: 2

Views: 289

Answers (2)

thecoop
thecoop

Reputation: 46098

On your second call to the HighScoreList ctor, you're passing in an instance of HighScoreList<GenericScore> as the List<GenericStore> ctor argument, but HighScoreList<T> doesn't inherit off List<T>, hence the error.

As a point of style, generic type names usually start with T, so it'll be HighScoreList<TScoreType>, or just HighScoreList<T>

Upvotes: 3

Thomas Levesque
Thomas Levesque

Reputation: 292415

    HighScoreList<GenericScore> target =
        new HighScoreList<GenericScore>(highScoreList);

In the code above, you're passing a HighScoreList<GenericScore> to the constructor of HighScoreList<GenericScore>, but it expects a List<GenericScore>

Isn't that what you want ?

    List<GenericScore> highScoreList = new List<GenericScore>()
            {
                new GenericScore("Person1",400),
                new GenericScore("Person2",200),
                new GenericScore("Person3",100)
            };

    HighScoreList<GenericScore> target =
        new HighScoreList<GenericScore>(highScoreList);

Upvotes: 6

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