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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Dynamic.Utils;
using System.Runtime.CompilerServices;
namespace System.Linq.Expressions.Compiler
{
// Suppose we have something like:
//
// (string s)=>()=>s.
//
// We wish to generate the outer as:
//
// Func<string> OuterMethod(Closure closure, string s)
// {
// object[] locals = new object[1];
// locals[0] = new StrongBox<string>();
// ((StrongBox<string>)locals[0]).Value = s;
// return ((DynamicMethod)closure.Constants[0]).CreateDelegate(typeof(Func<string>), new Closure(null, locals));
// }
//
// ... and the inner as:
//
// string InnerMethod(Closure closure)
// {
// object[] locals = closure.Locals;
// return ((StrongBox<string>)locals[0]).Value;
// }
//
// This class tracks that "s" was hoisted into a closure, as the 0th
// element in the array
//
/// <summary>
/// Stores information about locals and arguments that are hoisted into
/// the closure array because they're referenced in an inner lambda.
///
/// This class is sometimes emitted as a runtime constant for internal
/// use to hoist variables/parameters in quoted expressions
///
/// Invariant: this class stores no mutable state
/// </summary>
internal sealed class HoistedLocals
{
// The parent locals, if any
internal readonly HoistedLocals? Parent;
// A mapping of hoisted variables to their indexes in the array
internal readonly ReadOnlyDictionary<Expression, int> Indexes;
// The variables, in the order they appear in the array
internal readonly ReadOnlyCollection<ParameterExpression> Variables;
// A virtual variable for accessing this locals array
internal readonly ParameterExpression SelfVariable;
internal HoistedLocals(HoistedLocals? parent, ReadOnlyCollection<ParameterExpression> vars)
{
if (parent != null)
{
// Add the parent locals array as the 0th element in the array
vars = vars.AddFirst(parent.SelfVariable);
}
if (vars.Count != 0)
{
Dictionary<Expression, int> indexes = new Dictionary<Expression, int>(vars.Count);
for (int i = 0; i < vars.Count; i++)
{
indexes.Add(vars[i], i);
}
Indexes = new ReadOnlyDictionary<Expression, int>(indexes);
}
else
{
Indexes = ReadOnlyDictionary<Expression, int>.Empty;
}
Parent = parent;
Variables = vars;
SelfVariable = Expression.Variable(typeof(object[]), name: null);
}
internal ParameterExpression? ParentVariable => Parent?.SelfVariable;
internal static object[] GetParent(object[] locals)
{
return ((StrongBox<object[]>)locals[0]).Value!;
}
}
}
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