const Dictionary in c#

Question

I have a class in C# that contains a Dictionary, which I want to create and ensure nothing as added, edited or removed from this dictionary as long as the class which contains it exists.

readonly doesn't really help, once I tested and saw that I can add items after. Just for instance, I created an example:

public class DictContainer
{
    private readonly Dictionary<int, int> myDictionary;

    public DictContainer()
    {
        myDictionary = GetDictionary();
    }

    private Dictionary<int, int> GetDictionary()
    {
        Dictionary<int, int> myDictionary = new Dictionary<int, int>();

        myDictionary.Add(1, 2);
        myDictionary.Add(2, 4);
        myDictionary.Add(3, 6);

        return myDictionary;
    }

    public void Add(int key, int value)
    {
        myDictionary.Add(key, value);
    }

}

I want the Add method not to work. If possible, I want it not to even compile. Any suggestions?

Actually, I'm worried for it is code that will be open for a lot of people to change. So, even if I hide the Add method, it will be possible for someone to "innocently" create a method which add a key, or remove another. I want people to look and know they shouldn't change the dictionary in any ways. Just like I have with a const variable.

Strange requirements suggest your design has issues. You might want to rethink what you're attempting here. Otherwise, you can easily create your own implementation that does this. — , May 12 '09 at 16:57
You can implement your own Dictionary. Similar question: http://stackoverflow.com/questions/35002/does-c-have-a-way-of-giving-me-an-immutable-dictionary — bruno conde, May 12 '09 at 16:57

score 8 · Answer 1 · answered May 12 '09 at 16:56

Hide the Dictionary totally. Just provide a get method on the DictContainer class that retrieves items from the dictionary.

public class DictContainer
{
    private readonly Dictionary<int, int> myDictionary;

    public DictContainer()
    {
        myDictionary = GetDictionary();
    }

    private Dictionary<int, int> GetDictionary()
    {
        Dictionary<int, int> myDictionary = new Dictionary<int, int>();

        myDictionary.Add(1, 2);
        myDictionary.Add(2, 4);
        myDictionary.Add(3, 6);

        return myDictionary;
    }

    public this[int key]
    {
        return myDictionary[key];
    }
}

score 2 · Answer 2 · edited Dec 01 '21 at 16:02

2

Don't define the Add Method.

Keep the myDictionary variable private and expose a Getter/Indexer so that it can only be read from outside that class..

edited Dec 01 '21 at 16:02

cigien

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answered May 12 '09 at 16:56

Eoin Campbell

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score 1 · Answer 3 · edited Aug 11 '14 at 12:23

1

There's no built-in way to do that, consider using a wrapper class.

edited Aug 11 '14 at 12:23

Steven

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answered May 12 '09 at 16:56

arul

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score 0 · Answer 4 · answered Nov 11 '14 at 21:52

0

FYI, now it is built-in to .net 4.5.

http://msdn.microsoft.com/en-us/library/gg712875(v=vs.110).aspx

answered Nov 11 '14 at 21:52

batbaatar

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score 0 · Answer 5 · edited Dec 01 '21 at 16:01

0

Similar to Neil's answer:

Hide the Dictionary totally. Just provide a get method on the DictContainer class that retrieves items from the dictionary. If you want to use [] override you need getter settter method (atleast any one get/set)

public class DictContainer
{
    private readonly Dictionary<int, int> myDictionary;

    public DictContainer()
    {
        myDictionary = GetDictionary();
    }

    private Dictionary<int, int> GetDictionary()
    {
        Dictionary<int, int> myDictionary = new Dictionary<int, int>();

        myDictionary.Add(1, 2);
        myDictionary.Add(2, 4);
        myDictionary.Add(3, 6);

        return myDictionary;
    }

    public this[int key]
    {
        get => myDictionary[key];
    }
}

edited Dec 01 '21 at 16:01

cigien

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answered Dec 01 '21 at 15:10

GVyas

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6

@cigien I have changed the function to make it work => public this[int key] { get => myDictionary[key]; } – GVyas Dec 30 '21 at 07:01
I'm not sure what you mean. If you want to make edits to your answer to clarify something, please go ahead. – cigien Dec 30 '21 at 13:37

score 0 · Answer 6 · answered May 12 '09 at 17:17

interface IReadOnlyDic<Key, Value>
{
    void Add(Key key, Value value);
}
class ReadOnlyDic<Key, Value> : Dictionary<Key, Value>, IReadOnlyDic<Key, Value>
{
    public new void Add(Key key, Value value)
    {
        //throw an exception or do nothing
    }
    #region IReadOnlyDic<Key,Value> Members

    void IReadOnlyDic<Key, Value>.Add(Key key, Value value)
    {
        base.Add(key, value);
    }

    #endregion
}

to add custom items;

    IReadOnlyDic<int, int> dict = myDictInstance as IReadOnlyDic<int, int>;
    if (dict != null)
        dict.Add(1, 155);

score 0 · Answer 7 · answered May 12 '09 at 17:21

0

and this is another way

class ReadOnlyDic<Key, Value> : Dictionary<Key, Value>
{
    private bool _locked = false;

    public new void Add(Key key, Value value)
    {
        if (!_locked)
        {
            base.Add(key, value);
        }
        else
        {
            throw new ReadOnlyException();
        }
    }
    public void Lock()
    {
        _locked = true;
    }
}

answered May 12 '09 at 17:21

Tolgahan Albayrak

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+1 for the simplicity of the solution, and for compatibility with the Dictionary's interfaces. However: Why using "new" instead of "override"? Further, besides the Add, the Remove method should be overridden, too. – chiccodoro May 06 '10 at 08:33
@chiccodoro: `Dictionary` does not have `virtual` methods. – SLaks May 10 '10 at 17:27

const Dictionary in c#

7 Answers7