src/Repository/Hierarchy/LoggerKey.cs

#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;

namespace log4net.Repository.Hierarchy
{
	/// <summary>
	/// Used internally to accelerate hash table searches.
	/// </summary>
	/// <remarks>
	/// <para>
	/// Internal class used to improve performance of 
	/// string keyed hashtables.
	/// </para>
	/// <para>
	/// The hashcode of the string is cached for reuse.
	/// The string is stored as an interned value.
	/// When comparing two <see cref="LoggerKey"/> objects for equality 
	/// the reference equality of the interned strings is compared.
	/// </para>
	/// </remarks>
	/// <author>Nicko Cadell</author>
	/// <author>Gert Driesen</author>
	internal sealed class LoggerKey
	{
		#region Internal Instance Constructors

		/// <summary>
		/// Construct key with string name
		/// </summary>
		/// <remarks>
		/// <para>
		/// Initializes a new instance of the <see cref="LoggerKey" /> class 
		/// with the specified name.
		/// </para>
		/// <para>
		/// Stores the hashcode of the string and interns
		/// the string key to optimize comparisons.
		/// </para>
		/// <note>
		/// The Compact Framework 1.0 the <see cref="String.Intern"/>
		/// method does not work. On the Compact Framework
		/// the string keys are not interned nor are they
		/// compared by reference.
		/// </note>
		/// </remarks>
		/// <param name="name">The name of the logger.</param>
		internal LoggerKey(string name) 
		{
#if NETCF || NETSTANDARD1_3
			// NETCF: String.Intern causes Native Exception
			m_name = name;
#else
			m_name = string.Intern(name);
#endif
			m_hashCache = name.GetHashCode();
		}

		#endregion Internal Instance Constructors

		#region Override implementation of Object

		/// <summary>
		/// Returns a hash code for the current instance.
		/// </summary>
		/// <returns>A hash code for the current instance.</returns>
		/// <remarks>
		/// <para>
		/// Returns the cached hashcode.
		/// </para>
		/// </remarks>
		override public int GetHashCode() 
		{
			return m_hashCache;
		}

		/// <summary>
		/// Determines whether two <see cref="LoggerKey" /> instances 
		/// are equal.
		/// </summary>
		/// <param name="obj">The <see cref="object" /> to compare with the current <see cref="LoggerKey" />.</param>
		/// <returns>
		/// <c>true</c> if the specified <see cref="object" /> is equal to the current <see cref="LoggerKey" />; otherwise, <c>false</c>.
		/// </returns>
		/// <remarks>
		/// <para>
		/// Compares the references of the interned strings.
		/// </para>
		/// </remarks>
		override public bool Equals(object obj) 
		{
			// Compare reference type of this against argument
			if (((object)this) == obj)
			{
				return true;
			}
			
			LoggerKey objKey = obj as LoggerKey;
			if (objKey != null) 
			{
#if NETCF || NETSTANDARD1_3
				return ( m_name == objKey.m_name );
#else
				// Compare reference types rather than string's overloaded ==
				return ( ((object)m_name) == ((object)objKey.m_name) );
#endif
			}
			return false;
		}

		#endregion

		#region Private Instance Fields

		private readonly string m_name;  
		private readonly int m_hashCache;

		#endregion Private Instance Fields
	}	
}