Question

I am trying to learn generic types and I’ve written this code:

public class MyProp<TDictonary, TValor>
    {
        private List<TDictonary> MyDictionary = new List<TDictonary>();
        private List<TValor> TValue = new List<TValue>();

        public MyProp<TDictonary, TValue> Search(TDictonary dictionary)
        {
            MyProp<TDictonary, TValor> dic = new MyProp<TDictonary, TValor>();
            var test = MyDictionary.FirstOrDefault(item => item == dictionary);
            return dic;
        }

So I tried to create something like a C# Dictionary. What I tried to do was to associate TDictionary and TValue to Lists, add them to my generic type and return MyProp with its content. I also plan to add other methods like Add, Remove, etc, but if I’m not able to perform a simple search within a list I certainly won’t be able to go any further.

Does anyone know if I’m going down the right path? If not, could you point to the right path?

Thank you.

Answer 1

I tried to create something like a C# Dictionary

You do know about System.Collections.Generic.Dictionary<TKey, TValue> though, right?

Anyway, I’m not sure what your generics (or even the type) are actually meant to represent (give them clearer names!), so I cannot exactly tell you what you have to change to actually search on your dictionary.

However there are a few hints:

• In the method, you create an instance dic, do nothing on it and then simply return that – regardless of what you do previously.
• You only work on the MyDictionary but completely ignore the TValue field.
• Private fields are usually named in camelCase, i.e. starting a lower case character.
• Naming a private field TValue is very confusing, due to the starting T. That is usually reserved for generic types only.

It gives me this error: Error 1 Operator ‘==’ cannot be applied to operands of type ‘TDictonary’ and ‘TDictonary’

That’s because the type is a generic type without any restrictions. So it can either be a reference type or a value type, as such the compiler cannot decide about which comparison to do for the == operator. A simple, but maybe restricting, fix would be to specify a base type that is either a value type, or a reference type:

public class MyProp<TDictonary, TValor>
    where TDictionary : class