Errors with creating arrays and accessing information

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I've written some code here

C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Tests
{
    public class KeyValueStatusGroup<TKey, TValue, TStatus>
    {
        public TKey Key;
        public ValueStatusPair<TValue, TStatus> ValueStatusPair = new ValueStatusPair<TValue, TStatus>(); 
    }

    public class ValueStatusPair<TValue, TStatus>
    {
        public TValue Value;
        public TStatus Status;
    }

    public class TriArray<TKey, TValue, TStatus>
    {
        private List<KeyValueStatusGroup<TKey, TValue, TStatus>> list = new List<KeyValueStatusGroup<TKey, TValue, TStatus>>();

        public ValueStatusPair<TValue, TStatus> this[TKey key]
        {
            get
            {
                foreach (KeyValueStatusGroup<TKey, TValue, TStatus> keyValueStatusGroup in list)
                {
                    if (keyValueStatusGroup.Key == key)
                    {
                        return keyValueStatusGroup.ValueStatusPair;
                    }
                }
            }
            set
            {
                foreach (KeyValueStatusGroup<TKey, TValue, TStatus> keyValueStatusGroup in list)
                {
                    if (keyValueStatusGroup.Key == key)
                    {
                        keyValueStatusGroup.ValueStatusPair = value;
                    }
                }
            }
        }
    }
}

I think it should work fine but I'm getting an error that says:
Operator '==' cannot be applied to operands of type 'TKey' and 'TKey'

What is the problem and how can I fix it???

Thanks Jake

Posted 12-Jan-14 20:11pm

The Kcrownikown

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3 solutions

Solution 2

TKey, TValue and TStatus - as you use them are NOT real types!!!
This is a kind of notation to declare placeholders for generic types (http://msdn.microsoft.com/en-us/library/512aeb7t.aspx[^]).
When you use your new type KeyValueStatusGroup (new) you have to declare the de-facto types instead of TKey, TValue and TStatus...

Posted 12-Jan-14 20:21pm

Kornfeld Eliyahu Peter

Solution 3

If you change the ValueStatusPair Property to:

C#

public ValueStatusPair<TValue, TStatus> this[TKey key]
{
    get
    {
        foreach (KeyValueStatusGroup<TKey, TValue, TStatus> keyValueStatusGroup in list)
        {
            // use reference equality, not value equality
            if (keyValueStatusGroup.Equals(key))
            {
                return keyValueStatusGroup.ValueStatusPair;
            }
        }
         
        // all paths must have a return value !
        return null;
    }
    set
    {
        foreach (KeyValueStatusGroup<TKey, TValue, TStatus> keyValueStatusGroup in list)
        {
            // use reference equality, not value equality
            if (keyValueStatusGroup.Equals(key))
            {
                keyValueStatusGroup.ValueStatusPair = value;
            }
        }
    }
}

It will compile, but I haven't had time to test your code, or grok its design.

My impression is you are implementing a generic Tuple with three elements of certain generic types.

Posted 12-Jan-14 21:43pm

BillWoodruff

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Gitanjali Singh · Accepted Answer · 2014-01-12T20:15:00

This happens because KeyValuePair<tkey,> does not define a custom == operator and is not included in the predefined list of value types that can use it.
Refer:http://msdn.microsoft.com/en-us/library/53k8ybth%28v=VS.100%29.aspx[^]

Quote:
For predefined value types, the equality operator (==) returns true if the values of its operands are equal, false otherwise.

Your best bet for an equality check in this case, because this is not a struct you have control over, is to call default(KeyValuePair<tkey,tvalue>).Equals(pair) instead.