C# SyntheticBoundNodeFactory.ArrayAccessFirstElement方法代码示例

        private BoundStatement InitializeFixedStatementArrayLocal(
            LocalSymbol localSymbol,
            BoundFixedLocalCollectionInitializer fixedInitializer,
            SyntheticBoundNodeFactory factory,
            out LocalSymbol arrayTemp)
        {
            // From ExpressionBinder::BindPtrToArray:
            // (((temp = array) != null && temp.Length > 0) ? loc = &temp[0] : loc = null)
            // NOTE: The assignment needs to be inside the EK_QUESTIONMARK. See Whidbey bug #397859.
            // We can't do loc = (... ? ... : ...) since the CLR type of &temp[0] is a managed
            // pointer and null is a UIntPtr - which confuses the JIT. We can't just convert
            // &temp[0] to UIntPtr with a conv.u instruction because then if a GC occurs between
            // the time of the cast and the assignment to the local, we're toast.

            TypeSymbol localType = localSymbol.Type;
            BoundExpression initializerExpr = VisitExpression(fixedInitializer.Expression);
            TypeSymbol initializerType = initializerExpr.Type;

            arrayTemp = factory.SynthesizedLocal(initializerType);
            ArrayTypeSymbol arrayType = (ArrayTypeSymbol)arrayTemp.Type;
            TypeSymbol arrayElementType = arrayType.ElementType;
            int arrayRank = arrayType.Rank;

            // NOTE: we pin the pointer, not the array.
            Debug.Assert(!arrayTemp.IsPinned);
            Debug.Assert(localSymbol.IsPinned);

            //(temp = array)
            BoundExpression arrayTempInit = factory.AssignmentExpression(factory.Local(arrayTemp), initializerExpr);

            //(temp = array) != null
            BoundExpression notNullCheck = MakeNullCheck(factory.Syntax, arrayTempInit, BinaryOperatorKind.NotEqual);

            BoundExpression lengthCall;

            if (arrayRank == 1)
            {
                lengthCall = factory.ArrayLength(factory.Local(arrayTemp));
            }
            else
            {
                MethodSymbol lengthMethod;
                if (TryGetWellKnownTypeMember(fixedInitializer.Syntax, WellKnownMember.System_Array__get_Length, out lengthMethod))
                {
                    lengthCall = factory.Call(factory.Local(arrayTemp), lengthMethod);
                }
                else
                {
                    lengthCall = new BoundBadExpression(fixedInitializer.Syntax, LookupResultKind.NotInvocable, ImmutableArray<Symbol>.Empty, ImmutableArray.Create<BoundNode>(factory.Local(arrayTemp)), ErrorTypeSymbol.UnknownResultType);
                }
            }

            // NOTE: dev10 comment says ">", but code actually checks "!="
            //temp.Length != 0
            BoundExpression lengthCheck = factory.Binary(BinaryOperatorKind.IntNotEqual, factory.SpecialType(SpecialType.System_Boolean), lengthCall, factory.Literal(0));

            //((temp = array) != null && temp.Length != 0)
            BoundExpression condition = factory.Binary(BinaryOperatorKind.LogicalBoolAnd, factory.SpecialType(SpecialType.System_Boolean), notNullCheck, lengthCheck);

            //temp[0]
            BoundExpression firstElement = factory.ArrayAccessFirstElement(factory.Local(arrayTemp));

            // NOTE: this is a fixed statement address-of in that it's the initial value of pinned local.
            //&temp[0]
            BoundExpression firstElementAddress = new BoundAddressOfOperator(factory.Syntax, firstElement, isFixedStatementAddressOf: true, type: new PointerTypeSymbol(arrayElementType));
            BoundExpression convertedFirstElementAddress = factory.Convert(
                localType,
                firstElementAddress, 
                fixedInitializer.ElementPointerTypeConversion);

            //loc = &temp[0]
            BoundExpression consequenceAssignment = factory.AssignmentExpression(factory.Local(localSymbol), convertedFirstElementAddress);

            //loc = null
            BoundExpression alternativeAssignment = factory.AssignmentExpression(factory.Local(localSymbol), factory.Null(localType));

            //(((temp = array) != null && temp.Length != 0) ? loc = &temp[0] : loc = null)
            BoundStatement localInit = factory.ExpressionStatement(
                new BoundConditionalOperator(factory.Syntax, condition, consequenceAssignment, alternativeAssignment, ConstantValue.NotAvailable, localType));

            return AddLocalDeclarationSequencePointIfNecessary(fixedInitializer.Syntax.Parent.Parent, localSymbol, localInit);
        }