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// Copyright (c) AlphaSierraPapa for the SharpDevelop Team
//
// Permission is hereby granted, free of charge, to any person obtaining a copy of this
// software and associated documentation files (the "Software"), to deal in the Software
// without restriction, including without limitation the rights to use, copy, modify, merge,
// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
// to whom the Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all copies or
// substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.
using System;
using System.Collections.Generic;
using System.Diagnostics.Contracts;
namespace ICSharpCode.NRefactory.TypeSystem
{
/// <summary>
/// Provider used for interning.
/// </summary>
/// <remarks>
/// A simple IInterningProvider implementation could use 3 dictionaries:
/// 1. using value equality comparer (for certain types known to implement value equality, e.g. string and IType)
/// 2. using comparer that calls into ISupportsInterning (for types implementing ISupportsInterning)
/// 3. list comparer (for InternList method)
///
/// On the first Intern()-call, the provider tells the object to prepare for interning (ISupportsInterning.PrepareForInterning)
/// and stores it into a dictionary. On further Intern() calls, the original object is returned for all equal objects.
/// This allows reducing the memory usage by using a single object instance where possible.
///
/// Interning provider implementations could also use the interning logic for different purposes:
/// for example, it could be used to determine which objects are used jointly between multiple type definitions
/// and which are used only within a single type definition. Then a persistent file format could be organized so
/// that shared objects are loaded only once, yet non-shared objects get loaded lazily together with the class.
/// </remarks>
#if WITH_CONTRACTS
[ContractClass(typeof(IInterningProviderContract))]
#endif
public interface IInterningProvider
{
/// <summary>
/// Interns the specified object.
/// The object must implement <see cref="ISupportsInterning"/>, or must be of one of the types
/// known to the interning provider to use value equality,
/// otherwise it will be returned without being interned.
/// </summary>
T Intern<T>(T obj) where T : class;
IList<T> InternList<T>(IList<T> list) where T : class;
}
#if WITH_CONTRACTS
[ContractClassFor(typeof(IInterningProvider))]
abstract class IInterningProviderContract : IInterningProvider
{
T IInterningProvider.Intern<T>(T obj)
{
Contract.Ensures((Contract.Result<T>() == null) == (obj == null));
return obj;
}
IList<T> IInterningProvider.InternList<T>(IList<T> list)
{
Contract.Ensures((Contract.Result<IList<T>>() == null) == (list == null));
return list;
}
}
#endif
}
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