#region Apache License
|
//
|
// Licensed to the Apache Software Foundation (ASF) under one or more
|
// contributor license agreements. See the NOTICE file distributed with
|
// this work for additional information regarding copyright ownership.
|
// The ASF licenses this file to you under the Apache License, Version 2.0
|
// (the "License"); you may not use this file except in compliance with
|
// the License. You may obtain a copy of the License at
|
//
|
// http://www.apache.org/licenses/LICENSE-2.0
|
//
|
// Unless required by applicable law or agreed to in writing, software
|
// distributed under the License is distributed on an "AS IS" BASIS,
|
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
// See the License for the specific language governing permissions and
|
// limitations under the License.
|
//
|
#endregion
|
|
using System;
|
using System.Collections;
|
|
namespace log4net.Util
|
{
|
/// <summary>
|
/// An always empty <see cref="IDictionaryEnumerator"/>.
|
/// </summary>
|
/// <remarks>
|
/// <para>
|
/// A singleton implementation of the <see cref="IDictionaryEnumerator"/> over a collection
|
/// that is empty and not modifiable.
|
/// </para>
|
/// </remarks>
|
/// <author>Nicko Cadell</author>
|
/// <author>Gert Driesen</author>
|
public sealed class NullDictionaryEnumerator : IDictionaryEnumerator
|
{
|
#region Private Instance Constructors
|
|
/// <summary>
|
/// Initializes a new instance of the <see cref="NullDictionaryEnumerator" /> class.
|
/// </summary>
|
/// <remarks>
|
/// <para>
|
/// Uses a private access modifier to enforce the singleton pattern.
|
/// </para>
|
/// </remarks>
|
private NullDictionaryEnumerator()
|
{
|
}
|
|
#endregion Private Instance Constructors
|
|
#region Public Static Properties
|
|
/// <summary>
|
/// Gets the singleton instance of the <see cref="NullDictionaryEnumerator" />.
|
/// </summary>
|
/// <returns>The singleton instance of the <see cref="NullDictionaryEnumerator" />.</returns>
|
/// <remarks>
|
/// <para>
|
/// Gets the singleton instance of the <see cref="NullDictionaryEnumerator" />.
|
/// </para>
|
/// </remarks>
|
public static NullDictionaryEnumerator Instance
|
{
|
get { return s_instance; }
|
}
|
|
#endregion Public Static Properties
|
|
#region Implementation of IEnumerator
|
|
/// <summary>
|
/// Gets the current object from the enumerator.
|
/// </summary>
|
/// <remarks>
|
/// Throws an <see cref="InvalidOperationException" /> because the
|
/// <see cref="NullDictionaryEnumerator" /> never has a current value.
|
/// </remarks>
|
/// <remarks>
|
/// <para>
|
/// As the enumerator is over an empty collection its <see cref="Current"/>
|
/// value cannot be moved over a valid position, therefore <see cref="Current"/>
|
/// will throw an <see cref="InvalidOperationException"/>.
|
/// </para>
|
/// </remarks>
|
/// <exception cref="InvalidOperationException">The collection is empty and <see cref="Current"/>
|
/// cannot be positioned over a valid location.</exception>
|
public object Current
|
{
|
get { throw new InvalidOperationException(); }
|
}
|
|
/// <summary>
|
/// Test if the enumerator can advance, if so advance.
|
/// </summary>
|
/// <returns><c>false</c> as the <see cref="NullDictionaryEnumerator" /> cannot advance.</returns>
|
/// <remarks>
|
/// <para>
|
/// As the enumerator is over an empty collection its <see cref="Current"/>
|
/// value cannot be moved over a valid position, therefore <see cref="MoveNext"/>
|
/// will always return <c>false</c>.
|
/// </para>
|
/// </remarks>
|
public bool MoveNext()
|
{
|
return false;
|
}
|
|
/// <summary>
|
/// Resets the enumerator back to the start.
|
/// </summary>
|
/// <remarks>
|
/// <para>
|
/// As the enumerator is over an empty collection <see cref="Reset"/> does nothing.
|
/// </para>
|
/// </remarks>
|
public void Reset()
|
{
|
}
|
|
#endregion Implementation of IEnumerator
|
|
#region Implementation of IDictionaryEnumerator
|
|
/// <summary>
|
/// Gets the current key from the enumerator.
|
/// </summary>
|
/// <remarks>
|
/// Throws an exception because the <see cref="NullDictionaryEnumerator" />
|
/// never has a current value.
|
/// </remarks>
|
/// <remarks>
|
/// <para>
|
/// As the enumerator is over an empty collection its <see cref="Current"/>
|
/// value cannot be moved over a valid position, therefore <see cref="Key"/>
|
/// will throw an <see cref="InvalidOperationException"/>.
|
/// </para>
|
/// </remarks>
|
/// <exception cref="InvalidOperationException">The collection is empty and <see cref="Current"/>
|
/// cannot be positioned over a valid location.</exception>
|
public object Key
|
{
|
get { throw new InvalidOperationException(); }
|
}
|
|
/// <summary>
|
/// Gets the current value from the enumerator.
|
/// </summary>
|
/// <value>The current value from the enumerator.</value>
|
/// <remarks>
|
/// Throws an <see cref="InvalidOperationException" /> because the
|
/// <see cref="NullDictionaryEnumerator" /> never has a current value.
|
/// </remarks>
|
/// <remarks>
|
/// <para>
|
/// As the enumerator is over an empty collection its <see cref="Current"/>
|
/// value cannot be moved over a valid position, therefore <see cref="Value"/>
|
/// will throw an <see cref="InvalidOperationException"/>.
|
/// </para>
|
/// </remarks>
|
/// <exception cref="InvalidOperationException">The collection is empty and <see cref="Current"/>
|
/// cannot be positioned over a valid location.</exception>
|
public object Value
|
{
|
get { throw new InvalidOperationException(); }
|
}
|
|
/// <summary>
|
/// Gets the current entry from the enumerator.
|
/// </summary>
|
/// <remarks>
|
/// Throws an <see cref="InvalidOperationException" /> because the
|
/// <see cref="NullDictionaryEnumerator" /> never has a current entry.
|
/// </remarks>
|
/// <remarks>
|
/// <para>
|
/// As the enumerator is over an empty collection its <see cref="Current"/>
|
/// value cannot be moved over a valid position, therefore <see cref="Entry"/>
|
/// will throw an <see cref="InvalidOperationException"/>.
|
/// </para>
|
/// </remarks>
|
/// <exception cref="InvalidOperationException">The collection is empty and <see cref="Current"/>
|
/// cannot be positioned over a valid location.</exception>
|
public DictionaryEntry Entry
|
{
|
get { throw new InvalidOperationException(); }
|
}
|
|
#endregion Implementation of IDictionaryEnumerator
|
|
#region Private Static Fields
|
|
/// <summary>
|
/// The singleton instance of the <see cref="NullDictionaryEnumerator" />.
|
/// </summary>
|
private readonly static NullDictionaryEnumerator s_instance = new NullDictionaryEnumerator();
|
|
#endregion Private Static Fields
|
}
|
}
|
