Best way to translate from IDictionary to a generic IDictionary

I've got an IDictionary field that I would like to expose via a property of type IDictionary<string, dynamic> the conversion is surprisingly difficult since I have no idea what I can .Cast<>() the IDictionary to.

Best I've got:

IDictionary properties;
protected virtual IDictionary<string, dynamic> Properties {
  get { 
        return _properties.Keys.Cast<string>()
            开发者_StackOverflow中文版  .ToDictionary(name=>name, name=> _properties[name] as dynamic); 
      }
    }

If the underlying type of the IDictionary does not implement IDictionary<string, dynamic>, you cannot cast the object, period. If it does, a simple cast via (IDictionary<string, dynamic>)localVar will suffice.

If it's not, there are two things you can do:

1. Copy the IDictionary to your generic type.
2. Build an Adapter class that accepts the IDictionary as a dependency and implements the generic IDictionary you want, mapping calls from one to the other.

Edit: The sample code you've just posted will copy the dictionary every time it gets called! I will edit again in a moment with some suggested code.

Option 1

your sample code approach is solid as a means of copying the data, but the copy should be cached or you're going to copy lots of times. I'd suggest you put the actual translation code into a separate method and call that from your property the first time it's used. For example:

private IDictionary dataLayerProperties; 
private IDictionary<string, dynamic> translatedProperties = null;
protected virtual IDictionary<string, dynamic> Properties
{
    if(translatedProperties == null)
    {
        translatedProperties = TranslateDictionary(dataLayerProperties);        
    }  
    return translatedProperties;
}

public IDictionary<string, dynamic> TranslateDictionary(IDictionary values)
{
    return values.Keys.Cast<string>().ToDictionary(key=>key, key => values[key] as dynamic);            
}

Now, there are obvious cons to this approach... what if dataLayerProperties needs to be refreshed? You have to go setting translatedProperties to null again, etc.

Option 2

This is my preferred approach.

public class TranslatedDictionary : IDictionary<string, dynamic>
{
    private IDictionary Original = null;

    public TranslatedDictionary(IDictionary original)
    {
        Original = original;
    }
    public ICollection<string> Keys
    {
        get
        {
            return Original.Keys.Cast<string>().ToList();
        }
    }

    public dynamic this[string key]
    {
        get
        {
            return Original[key] as dynamic;
        }
        set
        {
            Original[key] = value;
        }
    }
    // and so forth, for each method of IDictionary<string, dynamic>
}

//elsewhere, using your original property and field names:
Properties = new TranslatedDictionary(properties);

Now, there are obvious cons to this approach as well, the most glaring is the fact that the Keys (and Value and anything else that returns ICollection on IDictionary has to return a new array for every call. But this still allows the most flexible approach, since it ensures the data is always up to date.

Unless the backing type for the IDictionary instance already implements IDictionary<string,dynamic> (like Dictionary<string,dynamic>) then casting won't help you. The Cast<>() method is only useful for returning IEnumerable<T> values and normal casting isn't an option.

If providing the data in the form of IDictionary<string,dynamic> is important, then why not go ahead and store it as a Dictionary<string,dynamic> from the start?

Here is a complete implementation of the approach recommended in the top answer. This was too big to fit as a comment.

    using System;
    using System.Collections;
    using System.Collections.Generic;
    using System.Diagnostics.CodeAnalysis;
    using System.Linq;

    /// <summary>
    /// The casted dictionary.
    /// </summary>
    /// <typeparam name="TKey">
    /// The key type
    /// </typeparam>
    /// <typeparam name="TValue">
    /// The value type
    /// </typeparam>
    public class CastedDictionary<TKey, TValue> : IDictionary<TKey, TValue>
    {
        /// <summary>
        /// The original dictionary.
        /// </summary>
        private readonly IDictionary originalDictionary;

        /// <summary>
        /// The keys.
        /// </summary>
        private ICollection<TKey> keys;

        /// <summary>
        /// The values.
        /// </summary>
        private ICollection<TValue> values;

        /// <summary>
        /// Initializes a new instance of the <see cref="CastedDictionary{TKey,TValue}"/> class.
        /// </summary>
        /// <param name="original">
        /// The original.
        /// </param>
        public CastedDictionary(IDictionary original)
            : this()
        {
            if (original == null)
            {
                throw new ArgumentNullException("original");
            }

            this.originalDictionary = original;
        }

        /// <summary>
        /// Prevents a default instance of the <see cref="CastedDictionary{TKey, TValue}"/> class from being created.
        /// </summary>
        [SuppressMessage("StyleCop.CSharp.DocumentationRules", "SA1642:ConstructorSummaryDocumentationMustBeginWithStandardText", Justification = "Style Cop does not analyze private generic class constructor comments properly")]
        private CastedDictionary()
        {
        }

        /// <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 this.originalDictionary.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 this.originalDictionary.IsReadOnly;
            }
        }

        /// <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 this.keys ?? (this.keys = this.originalDictionary.Keys.Cast<TKey>().ToList());
            }
        }

        /// <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 this.values ?? (this.values = this.originalDictionary.Values.Cast<TValue>().ToList());
            }
        }

        /// <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
            {
                return (TValue)this.originalDictionary[key];
            }

            set
            {
                this.originalDictionary[key] = value;
            }
        }

        /// <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 this.originalDictionary.Cast<KeyValuePair<TKey, TValue>>().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 this.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)
        {
            this.originalDictionary.Add(item.Key, item.Value);
        }

        /// <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()
        {
            this.originalDictionary.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 this.originalDictionary.Contains(item.Key) && EqualityComparer<TValue>.Default.Equals(this[item.Key], item.Value);
        }

        /// <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)
        {
            this.originalDictionary.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)
        {
            if (this.Contains(item))
            {
                this.originalDictionary.Remove(item.Key);
                return true;
            }

            return false;
        }

        /// <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 this.originalDictionary.Contains(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)
        {
            this.originalDictionary.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)
        {
            if (this.ContainsKey(key))
            {
                this.originalDictionary.Remove(key);
                return true;
            }

            return false;
        }

        /// <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)
        {
// ReSharper disable CompareNonConstrainedGenericWithNull
            if (typeof(TKey).IsValueType == false && key == null)
// ReSharper restore CompareNonConstrainedGenericWithNull
            {
                throw new ArgumentNullException("key");
            }

            if (this.ContainsKey(key))
            {
                value = this[key];
                return true;
            }

            value = default(TValue);
            return false;
        }
    }

You need to use a KeyValuePair.

myDictionary.Cast<KeyValuePair<Type1, Type2>>()