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/ 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / Core / Microsoft / Scripting / Ast / IArgumentProvider.cs / 1305376 / IArgumentProvider.cs
/* **************************************************************************** * * Copyright (c) Microsoft Corporation. * * This source code is subject to terms and conditions of the Microsoft Public License. A * copy of the license can be found in the License.html file at the root of this distribution. If * you cannot locate the Microsoft Public License, please send an email to * dlr@microsoft.com. By using this source code in any fashion, you are agreeing to be bound * by the terms of the Microsoft Public License. * * You must not remove this notice, or any other, from this software. * * * ***************************************************************************/ using System; using System.Collections.Generic; using System.Text; namespace System.Linq.Expressions { ////// Provides an internal interface for accessing the arguments that multiple tree /// nodes (DynamicExpression, ElementInit, MethodCallExpression, InvocationExpression, NewExpression, /// and InexExpression). /// /// This enables two optimizations which reduce the size of the trees. The first is it enables /// the nodes to hold onto an IList of T instead of a ReadOnlyCollection. This saves the cost /// of allocating the ReadOnlyCollection for each node. The second is that it enables specialized /// subclasses to be created which hold onto a specific number of arguments. For example Block2, /// Block3, Block4. These nodes can therefore avoid allocating both a ReadOnlyCollection and an /// array for storing their elements saving 32 bytes per node. /// /// Meanwhile the nodes can continue to expose the original LINQ properties of ReadOnlyCollections. They /// do this by re-using 1 field for storing both the array or an element that would normally be stored /// in the array. /// /// For the array case the collection is typed to IList of T instead of ReadOnlyCollection of T. /// When the node is initially constructed it is an array. When the compiler accesses the members it /// uses this interface. If a user accesses the members the array is promoted to a ReadOnlyCollection. /// /// For the object case we store the 1st argument in a field typed to object and when the node is initially /// constructed this holds directly onto the Expression. When the compiler accesses the members /// it again uses this interface and the accessor for the 1st argument uses Expression.ReturnObject to /// return the object which handles the Expression or ReadOnlyCollection case. When the user accesses /// the ReadOnlyCollection then the object field is updated to hold directly onto the ReadOnlyCollection. /// /// It is important that the Expressions consistently return the same ReadOnlyCollection otherwise the /// re-writer will be broken and it would be a breaking change from LINQ v1. The problem is that currently /// users can rely on object identity to tell if the node has changed. Storing the readonly collection in /// an overloaded field enables us to both reduce memory usage as well as maintain compatibility and an /// easy to use external API. /// internal interface IArgumentProvider { Expression GetArgument(int index); int ArgumentCount { get; } } static class ArgumentProviderOps { internal static T[] Map(this IArgumentProvider collection, Func select) { int count = collection.ArgumentCount; T[] result = new T[count]; count = 0; for (int i = 0; i < count; i++) { result[i] = select(collection.GetArgument(i)); } return result; } } } // File provided for Reference Use Only by Microsoft Corporation (c) 2007. // Copyright (c) Microsoft Corporation. All rights reserved.
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