Question

I am building the following class to manage a dictionary.

    public class EnumDictionary<TKey, TValue>
    {
        private Dictionary<TKey, TValue> _Dict;

        public EnumDictionary(Dictionary<TKey, TValue> Dict)
        {
            this._Dict = Dict;
        }

        public TKey GetValue(TValue value)
        {
            foreach (KeyValuePair<TKey, TValue> kvp in _Dict)
            {
                if (kvp.Value == value)
                    return kvp.Key;
            }

            throw new Exception("Undefined data type: " + value);
        }              
    }

But I am getting an error “Operator ‘==’ cannot be applied to operands of type ‘TValue’ and ‘TValue'”.

BTW, I am making this custom collection is because my dictionary has unique value, but I can’t get key by value from a dictionary.

Any help is appreciated. Thank you.

Answer 1

Did you try using the Equals method?

if (kvp.Value.Equals(value))

I think this restriction is due to the fact that the == operator can’t be used with all types. Take the following for instance:

struct Test
{
    public int Value;
}

Given the above struct, the following code will not compile:

Test a, b;
a = b = new Test();
bool areEqual = a == b; // Operator '==' cannot be applied to 
                        // operands of type 'Test' and 'Test'

However, all types have the Equals method, so calling that will work:

Test a, b;
a = b = new Test();
bool areEqual = a.Equals(b);