C#•16mo ago

When creating C# generic classes with static functions should the return type concreate class types?

For example:

public class MyClass<TKey, TValue> : IBase
{
    TValue v;
    public Dictionary<TKey, TValue> myData = new Dictionary<TKey, TValue>();

    public Dictionary<TKey, TValue> GetData() { return myData; }

    public static MyClass<string, MyData> CreateMyData()
    {
        MyClass<string, MyData> tmp = new MyClass<string, MyData>();
        return tmp;
    }
}

public class MyClass<TKey, TValue> : IBase
{
    TValue v;
    public Dictionary<TKey, TValue> myData = new Dictionary<TKey, TValue>();

    public Dictionary<TKey, TValue> GetData() { return myData; }

    public static MyClass<string, MyData> CreateMyData()
    {
        MyClass<string, MyData> tmp = new MyClass<string, MyData>();
        return tmp;
    }
}

And what about returning the same class from deserialization?

public static MyClass<string, MyData> Deserialize(string filename)
{
    string jsonString = File.ReadAllText(filename);
    MyCall<string, MyData> tmp = JsonSerializer.Deserialize<MyClass<string, MyData>>(jsonStrin);
    return tmp;
}

public static MyClass<string, MyData> Deserialize(string filename)
{
    string jsonString = File.ReadAllText(filename);
    MyCall<string, MyData> tmp = JsonSerializer.Deserialize<MyClass<string, MyData>>(jsonStrin);
    return tmp;
}

5 Replies

ero•16mo ago

i'm unclear about the question? you likely wouldn't have a CreateMyData which returns one specific definition of your generic class so you could have

public class MyClass<TKey, TValue> : IBase
{
  public static MyClass<TKey, TValue> CreateMyData()
  {
    MyClass<TKey, TValue> tmp = new MyClass<TKey, TValue>();
    return tmp;
  }
}

public class MyClass<TKey, TValue> : IBase
{
  public static MyClass<TKey, TValue> CreateMyData()
  {
    MyClass<TKey, TValue> tmp = new MyClass<TKey, TValue>();
    return tmp;
  }
}

which would be entirely pointless because you can just do new MyClass<TKey, TValue>() anywhere in your code without that Create method you probably need to constrain TKey to notnull, and your GetData method is also pretty pointless

r2d25551OP•16mo ago

Makes sense. That actually was my initial problem. My original design was from a C++ perspective. The return type could be derived from the baseclass. But that caused problems for the compiler. Now I am rewriting my code, hopefully, that can use the new desing in another class. Dictionary<string, BaseClass> myData; Dictionay<string, DerivedClass> myData; . And using an interface for Dictionary<string, BaseClass> GetData() { . . } . That caused problems for me. So now I am trying to write with generics. . . am I headed in the right direction?

ero•16mo ago

you'll always have this problem when you work with dictionaries all variations of dictionary have TKey and TValue as invariant

r2d25551OP•16mo ago

That would seem needed though. Almost like the compiler itself. C++ handles it differently. I am going to make my changes and see what happens. Bottom line, I want my worker class processing these classes to deal with a common and reliable interface. Thank you for the help. I will report back later of success or more problems 😄

Accord•16mo ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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When creating C# generic classes with static functions should the return type concreate class types?