How can return reference to Dictionary from a method as readonly?

Question

I want to let users iterate through my dictionary without modifying it.

I considertwo solutions:

1.ReadOnlyDictionary -- is there an implementation of that available?

2.Copy the entire dictionary -- what is the most efficient way to copy it ?

Thanks

Answer 1

Expose an enumeration(IEnumerable).

Edit: Example:

class A : IEnumerable<B>
{
  ...
  public IEnumerator<B> GetEnumerator ( )
  {
    return _dictionary.GetEnumerator ( );
  }
  private Dictionary<B> _dictionary;
}

Answer 2

If you only want to provide enumeration, you could expose it as IEnumerable of the Key/Value pair type. However, this obviously restricts some of the read-only tasks that can be performed.

Another option is to write a new class, derived from IDictionary<TKey, TValue> that provides read-only access by mapping those calls through to your real, wrapped dictionary, and throwing exceptions on any modifying calls like Add.

Answer 3

The easiest way to do this would probably be to implement your own collection that is a wrapper around a Dictionary, something along the lines of:

public class ReadOnlyDictionary<T, U>
{
    private IDictionary<T, U> BackingStore;

    public ReadOnlyDictionary<T, U>(IDictionary<T, U> baseDictionary) {
        this.BackingStore = baseDictionary;
    }

    public U this[T index] { get { return BackingStore[index]; } }

    // provide whatever other methods and/or interfaces you need
}

Answer 4

Keep in mind that your values will not be read only with the solutions provided for wrapping a Dictionary with only a property getter; For example:

ReadOnlyDictionary<int, Employee> readOnlyDict = GetDictionaryHoweverYouLike();
ReadOnlyDictionary[5].EmployeeName = "Ooops"

To do that you will also need to wrap your values in a read only wrapper class.