DefaultableDictionary.cs

using System;
using System.Collections;
using System.Collections.Generic;

namespace Ricoh
{
  /// <summary>
  /// Creates a wrapper around an IDictionary that allows for a default value to be returned when the specified key is not found.
  /// </summary>
  /// <typeparam name="TKey">The type of the dictionary key.</typeparam>
  /// <typeparam name="TValue">The type of the value stored in the dictionary.</typeparam>
  class DefaultableDictionary<TKey, TValue>: IDictionary<TKey, TValue>
  {
    private readonly IDictionary<TKey, TValue> _dictionary;
    private readonly TValue _defaultValue;

    /// <summary>Gets the number of elements contained in the <see cref="T:System.Collections.Generic.ICollection`1"/>.</summary>
    /// <returns>The number of elements contained in the <see cref="T:System.Collections.Generic.ICollection`1"/>.</returns>
    public int Count
    {
      get { return(_dictionary.Count); }
    }

    /// <summary>Gets a value indicating whether the <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only.</summary>
    /// <returns>true if the <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only; otherwise, false.</returns>
    public bool IsReadOnly 
    { 
      get { return(_dictionary.IsReadOnly); }
    }

    /// <summary>Gets or sets the element with the specified key.</summary>
    /// <returns>The element with the specified key.</returns>
    /// <param name="key">The key of the element to get or set.</param><exception cref="T:System.ArgumentNullException"><paramref name="key"/> is null.</exception><exception cref="T:System.Collections.Generic.KeyNotFoundException">The property is retrieved and <paramref name="key"/> is not found.</exception><exception cref="T:System.NotSupportedException">The property is set and the <see cref="T:System.Collections.Generic.IDictionary`2"/> is read-only.</exception>
    public TValue this[TKey key]
    {
      get
      {
        TValue value;
        TryGetValue(key, out value);
        return (value);
      }
      set { _dictionary[key] = value; }
    }

    /// <summary>Gets an <see cref="T:System.Collections.Generic.ICollection`1"/> containing the keys of the <see cref="T:System.Collections.Generic.IDictionary`2"/>.</summary>
    /// <returns>An <see cref="T:System.Collections.Generic.ICollection`1"/> containing the keys of the object that implements <see cref="T:System.Collections.Generic.IDictionary`2"/>.</returns>
    public ICollection<TKey> Keys
    {
      get { return (_dictionary.Keys); }
    }

    /// <summary>Gets an <see cref="T:System.Collections.Generic.ICollection`1"/> containing the values in the <see cref="T:System.Collections.Generic.IDictionary`2"/>.</summary>
    /// <returns>An <see cref="T:System.Collections.Generic.ICollection`1"/> containing the values in the object that implements <see cref="T:System.Collections.Generic.IDictionary`2"/>.</returns>
    public ICollection<TValue> Values
    {
      get { return (_dictionary.Values); }
    }

    /// <param name="dictionary">The dictionary object to wrap.</param>
    /// <param name="defaultValue">The default value to use or return if the requested key is not found in the dictionary.</param>
    public DefaultableDictionary(IDictionary<TKey, TValue> dictionary, TValue defaultValue)
    {
      if (dictionary == null) throw new ArgumentNullException("dictionary", "Cannot wrap a null dictionary with a default value.");

      _dictionary = dictionary;
      _defaultValue = defaultValue;
    }

    /// <summary>
    /// Returns an enumerator that iterates through the collection.
    /// </summary>
    /// <returns>
    /// A <see cref="T:System.Collections.Generic.IEnumerator`1"/> that can be used to iterate through the collection.
    /// </returns>
    /// <filterpriority>1</filterpriority>
    public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator()
    {
      return (_dictionary.GetEnumerator());
    }

    /// <summary>
    /// Returns an enumerator that iterates through a collection.
    /// </summary>
    /// <returns>
    /// An <see cref="T:System.Collections.IEnumerator"/> object that can be used to iterate through the collection.
    /// </returns>
    /// <filterpriority>2</filterpriority>
    IEnumerator IEnumerable.GetEnumerator()
    {
      return (_dictionary.GetEnumerator());
    }

    /// <summary>
    /// Adds an item to the <see cref="T:System.Collections.Generic.ICollection`1"/>.
    /// </summary>
    /// <param name="item">The object to add to the <see cref="T:System.Collections.Generic.ICollection`1"/>.</param><exception cref="T:System.NotSupportedException">The <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only.</exception>
    public void Add(KeyValuePair<TKey, TValue> item)
    {
      _dictionary.Add(item);
    }

    /// <summary>
    /// Removes all items from the <see cref="T:System.Collections.Generic.ICollection`1"/>.
    /// </summary>
    /// <exception cref="T:System.NotSupportedException">The <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only. </exception>
    public void Clear()
    {
      _dictionary.Clear();
    }

    /// <summary>
    /// Determines whether the <see cref="T:System.Collections.Generic.ICollection`1"/> contains a specific value.
    /// </summary>
    /// <returns>
    /// true if <paramref name="item"/> is found in the <see cref="T:System.Collections.Generic.ICollection`1"/>; otherwise, false.
    /// </returns>
    /// <param name="item">The object to locate in the <see cref="T:System.Collections.Generic.ICollection`1"/>.</param>
    public bool Contains(KeyValuePair<TKey, TValue> item)
    {
      return(_dictionary.Contains(item));
    }

    /// <summary>
    /// Copies the elements of the <see cref="T:System.Collections.Generic.ICollection`1"/> to an <see cref="T:System.Array"/>, starting at a particular <see cref="T:System.Array"/> index.
    /// </summary>
    /// <param name="array">The one-dimensional <see cref="T:System.Array"/> that is the destination of the elements copied from <see cref="T:System.Collections.Generic.ICollection`1"/>. The <see cref="T:System.Array"/> must have zero-based indexing.</param><param name="arrayIndex">The zero-based index in <paramref name="array"/> at which copying begins.</param><exception cref="T:System.ArgumentNullException"><paramref name="array"/> is null.</exception><exception cref="T:System.ArgumentOutOfRangeException"><paramref name="arrayIndex"/> is less than 0.</exception><exception cref="T:System.ArgumentException">The number of elements in the source <see cref="T:System.Collections.Generic.ICollection`1"/> is greater than the available space from <paramref name="arrayIndex"/> to the end of the destination <paramref name="array"/>.</exception>
    public void CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex)
    {
      _dictionary.CopyTo(array, arrayIndex);
    }

    /// <summary>
    /// Removes the first occurrence of a specific object from the <see cref="T:System.Collections.Generic.ICollection`1"/>.
    /// </summary>
    /// <returns>
    /// true if <paramref name="item"/> was successfully removed from the <see cref="T:System.Collections.Generic.ICollection`1"/>; otherwise, false. This method also returns false if <paramref name="item"/> is not found in the original <see cref="T:System.Collections.Generic.ICollection`1"/>.
    /// </returns>
    /// <param name="item">The object to remove from the <see cref="T:System.Collections.Generic.ICollection`1"/>.</param><exception cref="T:System.NotSupportedException">The <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only.</exception>
    public bool Remove(KeyValuePair<TKey, TValue> item)
    {
      return(_dictionary.Remove(item));
    }

    /// <summary>
    /// Determines whether the <see cref="T:System.Collections.Generic.IDictionary`2"/> contains an element with the specified key.
    /// </summary>
    /// <returns>
    /// true if the <see cref="T:System.Collections.Generic.IDictionary`2"/> contains an element with the key; otherwise, false.
    /// </returns>
    /// <param name="key">The key to locate in the <see cref="T:System.Collections.Generic.IDictionary`2"/>.</param><exception cref="T:System.ArgumentNullException"><paramref name="key"/> is null.</exception>
    public bool ContainsKey(TKey key)
    {
      return (_dictionary.ContainsKey(key));
    }

    /// <summary>
    /// Adds an element with the provided key and value to the <see cref="T:System.Collections.Generic.IDictionary`2"/>.
    /// </summary>
    /// <param name="key">The object to use as the key of the element to add.</param><param name="value">The object to use as the value of the element to add.</param><exception cref="T:System.ArgumentNullException"><paramref name="key"/> is null.</exception><exception cref="T:System.ArgumentException">An element with the same key already exists in the <see cref="T:System.Collections.Generic.IDictionary`2"/>.</exception><exception cref="T:System.NotSupportedException">The <see cref="T:System.Collections.Generic.IDictionary`2"/> is read-only.</exception>
    public void Add(TKey key, TValue value)
    {
      _dictionary.Add(key, value);
    }

    /// <summary>
    /// Removes the element with the specified key from the <see cref="T:System.Collections.Generic.IDictionary`2"/>.
    /// </summary>
    /// <returns>
    /// true if the element is successfully removed; otherwise, false.  This method also returns false if <paramref name="key"/> was not found in the original <see cref="T:System.Collections.Generic.IDictionary`2"/>.
    /// </returns>
    /// <param name="key">The key of the element to remove.</param><exception cref="T:System.ArgumentNullException"><paramref name="key"/> is null.</exception><exception cref="T:System.NotSupportedException">The <see cref="T:System.Collections.Generic.IDictionary`2"/> is read-only.</exception>
    public bool Remove(TKey key)
    {
      return (_dictionary.Remove(key));
    }

    /// <summary>
    /// Gets the value associated with the specified key.
    /// </summary>
    /// <returns>
    /// true if the object that implements <see cref="T:System.Collections.Generic.IDictionary`2"/> contains an element with the specified key; otherwise, false.
    /// </returns>
    /// <param name="key">The key whose value to get.</param><param name="value">When this method returns, the value associated with the specified key, if the key is found; otherwise, the default value for the type of the <paramref name="value"/> parameter. This parameter is passed uninitialized.</param><exception cref="T:System.ArgumentNullException"><paramref name="key"/> is null.</exception>
    public bool TryGetValue(TKey key, out TValue value)
    {
      if (! _dictionary.TryGetValue(key, out value)) {
        value = _defaultValue;
      }
      return(true);
    }
  }
}