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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.Diagnostics;
using System.Dynamic.Utils;
using AstUtils = System.Linq.Expressions.Utils;
namespace System.Linq.Expressions
{
/// <summary>
/// Represents an expression that has a conditional operator.
/// </summary>
[DebuggerTypeProxy(typeof(ConditionalExpressionProxy))]
public class ConditionalExpression : Expression
{
internal ConditionalExpression(Expression test, Expression ifTrue)
{
Test = test;
IfTrue = ifTrue;
}
internal static ConditionalExpression Make(Expression test, Expression ifTrue, Expression ifFalse, Type type)
{
if (ifTrue.Type != type || ifFalse.Type != type)
{
return new FullConditionalExpressionWithType(test, ifTrue, ifFalse, type);
}
if (ifFalse is DefaultExpression && ifFalse.Type == typeof(void))
{
return new ConditionalExpression(test, ifTrue);
}
else
{
return new FullConditionalExpression(test, ifTrue, ifFalse);
}
}
/// <summary>
/// Returns the node type of this Expression. Extension nodes should return
/// ExpressionType.Extension when overriding this method.
/// </summary>
/// <returns>The <see cref="ExpressionType"/> of the expression.</returns>
public sealed override ExpressionType NodeType => ExpressionType.Conditional;
/// <summary>
/// Gets the static type of the expression that this <see cref="Expression"/> represents.
/// </summary>
/// <returns>The <see cref="System.Type"/> that represents the static type of the expression.</returns>
public override Type Type => IfTrue.Type;
/// <summary>
/// Gets the test of the conditional operation.
/// </summary>
public Expression Test { get; }
/// <summary>
/// Gets the expression to execute if the test evaluates to true.
/// </summary>
public Expression IfTrue { get; }
/// <summary>
/// Gets the expression to execute if the test evaluates to false.
/// </summary>
public Expression IfFalse => GetFalse();
internal virtual Expression GetFalse()
{
// Using a singleton here to ensure a stable object identity for IfFalse, which Update relies on.
return AstUtils.Empty;
}
/// <summary>
/// Dispatches to the specific visit method for this node type.
/// </summary>
protected internal override Expression Accept(ExpressionVisitor visitor)
{
return visitor.VisitConditional(this);
}
/// <summary>
/// Creates a new expression that is like this one, but using the
/// supplied children. If all of the children are the same, it will
/// return this expression.
/// </summary>
/// <param name="test">The <see cref="Test"/> property of the result.</param>
/// <param name="ifTrue">The <see cref="IfTrue"/> property of the result.</param>
/// <param name="ifFalse">The <see cref="IfFalse"/> property of the result.</param>
/// <returns>This expression if no children changed, or an expression with the updated children.</returns>
public ConditionalExpression Update(Expression test, Expression ifTrue, Expression ifFalse)
{
if (test == Test && ifTrue == IfTrue && ifFalse == IfFalse)
{
return this;
}
return Expression.Condition(test, ifTrue, ifFalse, Type);
}
}
internal class FullConditionalExpression : ConditionalExpression
{
private readonly Expression _false;
internal FullConditionalExpression(Expression test, Expression ifTrue, Expression ifFalse)
: base(test, ifTrue)
{
_false = ifFalse;
}
internal override Expression GetFalse() => _false;
}
internal sealed class FullConditionalExpressionWithType : FullConditionalExpression
{
internal FullConditionalExpressionWithType(Expression test, Expression ifTrue, Expression ifFalse, Type type)
: base(test, ifTrue, ifFalse)
{
Type = type;
}
public sealed override Type Type { get; }
}
public partial class Expression
{
/// <summary>
/// Creates a <see cref="ConditionalExpression"/>.
/// </summary>
/// <param name="test">An <see cref="Expression"/> to set the <see cref="ConditionalExpression.Test"/> property equal to.</param>
/// <param name="ifTrue">An <see cref="Expression"/> to set the <see cref="ConditionalExpression.IfTrue"/> property equal to.</param>
/// <param name="ifFalse">An <see cref="Expression"/> to set the <see cref="ConditionalExpression.IfFalse"/> property equal to.</param>
/// <returns>A <see cref="ConditionalExpression"/> that has the <see cref="NodeType"/> property equal to
/// <see cref="ExpressionType.Conditional"/> and the <see cref="ConditionalExpression.Test"/>, <see cref="ConditionalExpression.IfTrue"/>,
/// and <see cref="ConditionalExpression.IfFalse"/> properties set to the specified values.</returns>
public static ConditionalExpression Condition(Expression test, Expression ifTrue, Expression ifFalse)
{
ExpressionUtils.RequiresCanRead(test, nameof(test));
ExpressionUtils.RequiresCanRead(ifTrue, nameof(ifTrue));
ExpressionUtils.RequiresCanRead(ifFalse, nameof(ifFalse));
if (test.Type != typeof(bool))
{
throw Error.ArgumentMustBeBoolean(nameof(test));
}
if (!TypeUtils.AreEquivalent(ifTrue.Type, ifFalse.Type))
{
throw Error.ArgumentTypesMustMatch();
}
return ConditionalExpression.Make(test, ifTrue, ifFalse, ifTrue.Type);
}
/// <summary>
/// Creates a <see cref="ConditionalExpression"/>.
/// </summary>
/// <param name="test">An <see cref="Expression"/> to set the <see cref="ConditionalExpression.Test"/> property equal to.</param>
/// <param name="ifTrue">An <see cref="Expression"/> to set the <see cref="ConditionalExpression.IfTrue"/> property equal to.</param>
/// <param name="ifFalse">An <see cref="Expression"/> to set the <see cref="ConditionalExpression.IfFalse"/> property equal to.</param>
/// <param name="type">A <see cref="Type"/> to set the <see cref="Type"/> property equal to.</param>
/// <returns>A <see cref="ConditionalExpression"/> that has the <see cref="NodeType"/> property equal to
/// <see cref="ExpressionType.Conditional"/> and the <see cref="ConditionalExpression.Test"/>, <see cref="ConditionalExpression.IfTrue"/>,
/// and <see cref="ConditionalExpression.IfFalse"/> properties set to the specified values.</returns>
/// <remarks>This method allows explicitly unifying the result type of the conditional expression in cases where the types of <paramref name="ifTrue"/>
/// and <paramref name="ifFalse"/> expressions are not equal. Types of both <paramref name="ifTrue"/> and <paramref name="ifFalse"/> must be implicitly
/// reference assignable to the result type. The <paramref name="type"/> is allowed to be <see cref="Void"/>.</remarks>
public static ConditionalExpression Condition(Expression test, Expression ifTrue, Expression ifFalse, Type type)
{
ExpressionUtils.RequiresCanRead(test, nameof(test));
ExpressionUtils.RequiresCanRead(ifTrue, nameof(ifTrue));
ExpressionUtils.RequiresCanRead(ifFalse, nameof(ifFalse));
ArgumentNullException.ThrowIfNull(type);
if (test.Type != typeof(bool))
{
throw Error.ArgumentMustBeBoolean(nameof(test));
}
if (type != typeof(void))
{
if (!TypeUtils.AreReferenceAssignable(type, ifTrue.Type) ||
!TypeUtils.AreReferenceAssignable(type, ifFalse.Type))
{
throw Error.ArgumentTypesMustMatch();
}
}
return ConditionalExpression.Make(test, ifTrue, ifFalse, type);
}
/// <summary>
/// Creates a <see cref="ConditionalExpression"/>.
/// </summary>
/// <param name="test">An <see cref="Expression"/> to set the <see cref="ConditionalExpression.Test"/> property equal to.</param>
/// <param name="ifTrue">An <see cref="Expression"/> to set the <see cref="ConditionalExpression.IfTrue"/> property equal to.</param>
/// <returns>A <see cref="ConditionalExpression"/> that has the <see cref="NodeType"/> property equal to
/// <see cref="ExpressionType.Conditional"/> and the <see cref="ConditionalExpression.Test"/>, <see cref="ConditionalExpression.IfTrue"/>,
/// properties set to the specified values. The <see cref="ConditionalExpression.IfFalse"/> property is set to default expression and
/// the type of the resulting <see cref="ConditionalExpression"/> returned by this method is <see cref="Void"/>.</returns>
public static ConditionalExpression IfThen(Expression test, Expression ifTrue)
{
return Condition(test, ifTrue, Expression.Empty(), typeof(void));
}
/// <summary>
/// Creates a <see cref="ConditionalExpression"/>.
/// </summary>
/// <param name="test">An <see cref="Expression"/> to set the <see cref="ConditionalExpression.Test"/> property equal to.</param>
/// <param name="ifTrue">An <see cref="Expression"/> to set the <see cref="ConditionalExpression.IfTrue"/> property equal to.</param>
/// <param name="ifFalse">An <see cref="Expression"/> to set the <see cref="ConditionalExpression.IfFalse"/> property equal to.</param>
/// <returns>A <see cref="ConditionalExpression"/> that has the <see cref="NodeType"/> property equal to
/// <see cref="ExpressionType.Conditional"/> and the <see cref="ConditionalExpression.Test"/>, <see cref="ConditionalExpression.IfTrue"/>,
/// and <see cref="ConditionalExpression.IfFalse"/> properties set to the specified values. The type of the resulting <see cref="ConditionalExpression"/>
/// returned by this method is <see cref="Void"/>.</returns>
public static ConditionalExpression IfThenElse(Expression test, Expression ifTrue, Expression ifFalse)
{
return Condition(test, ifTrue, ifFalse, typeof(void));
}
}
}
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