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/* ****************************************************************************
*
* 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.Linq.Expressions;
using Microsoft.Scripting.Utils;
namespace Microsoft.Scripting.Ast {
/// <summary>
/// Represents either a YieldBreak or YieldReturn in a GeneratorExpression
/// If Value is non-null, it's a YieldReturn; otherwise it's a YieldBreak
/// and executing it will stop enumeration of the generator, causing
/// MoveNext to return false.
/// </summary>
public sealed class YieldExpression : Expression {
private readonly LabelTarget _target;
private readonly Expression _value;
private readonly int _yieldMarker;
internal YieldExpression(LabelTarget target, Expression value, int yieldMarker) {
_target = target;
_value = value;
_yieldMarker = yieldMarker;
}
public override bool CanReduce {
get { return false; }
}
public sealed override Type Type {
get { return typeof(void); }
}
public sealed override ExpressionType NodeType {
get { return ExpressionType.Extension; }
}
/// <summary>
/// The value yieled from this expression, if it is a yield return
/// </summary>
public Expression Value {
get { return _value; }
}
/// <summary>
/// The label used to yield from this generator
/// </summary>
public LabelTarget Target {
get { return _target; }
}
public int YieldMarker {
get {
return _yieldMarker;
}
}
protected override Expression VisitChildren(ExpressionVisitor visitor) {
Expression v = visitor.Visit(_value);
if (v == _value) {
return this;
}
return Utils.MakeYield(_target, v, YieldMarker);
}
}
public partial class Utils {
public static YieldExpression YieldBreak(LabelTarget target) {
return MakeYield(target, null, -1);
}
public static YieldExpression YieldReturn(LabelTarget target, Expression value) {
return MakeYield(target, value, -1);
}
public static YieldExpression YieldReturn(LabelTarget target, Expression value, int yieldMarker) {
ContractUtils.RequiresNotNull(value, "value");
return MakeYield(target, value, yieldMarker);
}
public static YieldExpression MakeYield(LabelTarget target, Expression value, int yieldMarker) {
ContractUtils.RequiresNotNull(target, "target");
ContractUtils.Requires(target.Type != typeof(void), "target", "generator label must have a non-void type");
if (value != null) {
if (!TypeUtils.AreReferenceAssignable(target.Type, value.Type)) {
// C# autoquotes generator return values
if (target.Type.IsSubclassOf(typeof(Expression)) &&
TypeUtils.AreAssignable(target.Type, value.GetType())) {
value = Expression.Quote(value);
}
throw new ArgumentException(string.Format("Expression of type '{0}' cannot be yielded to a generator label of type '{1}'", value.Type, target.Type));
}
}
return new YieldExpression(target, value, yieldMarker);
}
}
}
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