Esempio n. 1
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        protected override Expr VisitCAST(ExprCast pExpr)
        {
            Debug.Assert(pExpr != null);

            Expr pArgument = pExpr.Argument;

            // If we have generated an identity cast or reference cast to a base class
            // we can omit the cast.
            if (pArgument.Type == pExpr.Type ||
                SymbolLoader.IsBaseClassOfClass(pArgument.Type, pExpr.Type) ||
                CConversions.FImpRefConv(GetSymbolLoader(), pArgument.Type, pExpr.Type))
            {
                return(Visit(pArgument));
            }

            // If we have a cast to PredefinedType.PT_G_EXPRESSION and the thing that we're casting is
            // a EXPRBOUNDLAMBDA that is an expression tree, then just visit the expression tree.
            if (pExpr.Type != null &&
                pExpr.Type.isPredefType(PredefinedType.PT_G_EXPRESSION) &&
                pArgument is ExprBoundLambda)
            {
                return(Visit(pArgument));
            }

            Expr result = GenerateConversion(pArgument, pExpr.Type, pExpr.isChecked());

            if ((pExpr.Flags & EXPRFLAG.EXF_UNBOXRUNTIME) != 0)
            {
                // Propagate the unbox flag to the call for the ExpressionTreeCallRewriter.
                result.Flags |= EXPRFLAG.EXF_UNBOXRUNTIME;
            }
            return(result);
        }
Esempio n. 2
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            private bool bindExplicitConversionFromArrayToArray(ArrayType arraySrc, ArrayType arrayDest)
            {
                // 13.2.2
                //
                // The explicit reference conversions are:
                //
                // * From an array-type S with an element type SE to an array-type T with an element type
                //   TE, provided all of the following are true:
                //
                //   * S and T differ only in element type. (In other words, S and T have the same number
                //     of dimensions.)
                //
                //   * An explicit reference conversion exists from SE to TE.

                if (arraySrc.rank != arrayDest.rank || arraySrc.IsSZArray != arrayDest.IsSZArray)
                {
                    return(false);  // Ranks do not match.
                }

                if (CConversions.FExpRefConv(GetSymbolLoader(), arraySrc.GetElementType(), arrayDest.GetElementType()))
                {
                    if (_needsExprDest)
                    {
                        _binder.bindSimpleCast(_exprSrc, _exprTypeDest, out _exprDest, EXPRFLAG.EXF_REFCHECK);
                    }
                    return(true);
                }

                return(false);
            }
Esempio n. 3
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            private AggCastResult bindExplicitConversionBetweenAggregates(AggregateType aggTypeDest)
            {
                // 13.2.3
                //
                // The explicit reference conversions are:
                //
                // * From object to any reference-type.
                // * From any class-type S to any class-type T, provided S is a base class of T.
                // * From any class-type S to any interface-type T, provided S is not sealed and
                //   provided S does not implement T.
                // * From any interface-type S to any class-type T, provided T is not sealed or provided
                //   T implements S.
                // * From any interface-type S to any interface-type T, provided S is not derived from T.

                Debug.Assert(_typeSrc != null);
                Debug.Assert(aggTypeDest != null);

                if (!(_typeSrc is AggregateType atSrc))
                {
                    return(AggCastResult.Failure);
                }

                AggregateSymbol aggSrc  = atSrc.getAggregate();
                AggregateSymbol aggDest = aggTypeDest.getAggregate();

                if (GetSymbolLoader().HasBaseConversion(aggTypeDest, atSrc))
                {
                    if (_needsExprDest)
                    {
                        if (aggDest.IsValueType() && aggSrc.getThisType().fundType() == FUNDTYPE.FT_REF)
                        {
                            _binder.bindSimpleCast(_exprSrc, _exprTypeDest, out _exprDest, EXPRFLAG.EXF_UNBOX);
                        }
                        else
                        {
                            _binder.bindSimpleCast(_exprSrc, _exprTypeDest, out _exprDest, EXPRFLAG.EXF_REFCHECK | (_exprSrc?.Flags & EXPRFLAG.EXF_CANTBENULL ?? 0));
                        }
                    }
                    return(AggCastResult.Success);
                }

                if ((aggSrc.IsClass() && !aggSrc.IsSealed() && aggDest.IsInterface()) ||
                    (aggSrc.IsInterface() && aggDest.IsClass() && !aggDest.IsSealed()) ||
                    (aggSrc.IsInterface() && aggDest.IsInterface()) ||
                    CConversions.HasGenericDelegateExplicitReferenceConversion(GetSymbolLoader(), _typeSrc, aggTypeDest))
                {
                    if (_needsExprDest)
                    {
                        _binder.bindSimpleCast(_exprSrc, _exprTypeDest, out _exprDest, EXPRFLAG.EXF_REFCHECK | (_exprSrc?.Flags & EXPRFLAG.EXF_CANTBENULL ?? 0));
                    }
                    return(AggCastResult.Success);
                }
                return(AggCastResult.Failure);
            }
Esempio n. 4
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            private bool bindExplicitConversionFromArrayToIList()
            {
                // 13.2.2
                //
                // The explicit reference conversions are:
                //
                // * From a one-dimensional array-type S[] to System.Collections.Generic.IList<T>, System.Collections.Generic.IReadOnlyList<T> and
                //   their base interfaces, provided there is an explicit reference conversion from S to T.

                Debug.Assert(_typeSrc != null);
                Debug.Assert(_typeDest != null);

                if (!(_typeSrc is ArrayType arrSrc) || !arrSrc.IsSZArray || !(_typeDest is AggregateType aggDest) ||
                    !aggDest.isInterfaceType() || aggDest.GetTypeArgsAll().Count != 1)
                {
                    return(false);
                }

                AggregateSymbol aggIList         = GetSymbolLoader().GetPredefAgg(PredefinedType.PT_G_ILIST);
                AggregateSymbol aggIReadOnlyList = GetSymbolLoader().GetPredefAgg(PredefinedType.PT_G_IREADONLYLIST);

                if ((aggIList == null ||
                     !GetSymbolLoader().IsBaseAggregate(aggIList, aggDest.getAggregate())) &&
                    (aggIReadOnlyList == null ||
                     !GetSymbolLoader().IsBaseAggregate(aggIReadOnlyList, aggDest.getAggregate())))
                {
                    return(false);
                }

                CType typeArr = arrSrc.GetElementType();
                CType typeLst = aggDest.GetTypeArgsAll()[0];

                if (!CConversions.FExpRefConv(GetSymbolLoader(), typeArr, typeLst))
                {
                    return(false);
                }

                if (_needsExprDest)
                {
                    _binder.bindSimpleCast(_exprSrc, _exprTypeDest, out _exprDest, EXPRFLAG.EXF_REFCHECK);
                }
                return(true);
            }
Esempio n. 5
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            private bool bindExplicitConversionFromIListToArray(ArrayType arrayDest)
            {
                // 13.2.2
                //
                // The explicit reference conversions are:
                //
                // * From System.Collections.Generic.IList<T>, System.Collections.Generic.IReadOnlyList<T> and their base interfaces
                //   to a one-dimensional array-type S[], provided there is an implicit or explicit reference conversion from
                //   S[] to System.Collections.Generic.IList<T> or System.Collections.Generic.IReadOnlyList<T>. This is precisely when either S and T
                //   are the same type or there is an implicit or explicit reference conversion from S to T.

                if (!arrayDest.IsSZArray || !(_typeSrc is AggregateType aggSrc) || !aggSrc.isInterfaceType() ||
                    aggSrc.GetTypeArgsAll().Count != 1)
                {
                    return(false);
                }

                AggregateSymbol aggIList         = GetSymbolLoader().GetPredefAgg(PredefinedType.PT_G_ILIST);
                AggregateSymbol aggIReadOnlyList = GetSymbolLoader().GetPredefAgg(PredefinedType.PT_G_IREADONLYLIST);

                if ((aggIList == null ||
                     !GetSymbolLoader().IsBaseAggregate(aggIList, aggSrc.getAggregate())) &&
                    (aggIReadOnlyList == null ||
                     !GetSymbolLoader().IsBaseAggregate(aggIReadOnlyList, aggSrc.getAggregate())))
                {
                    return(false);
                }

                CType typeArr = arrayDest.GetElementType();
                CType typeLst = aggSrc.GetTypeArgsAll()[0];

                Debug.Assert(!typeArr.IsNeverSameType());
                if (typeArr != typeLst && !CConversions.FExpRefConv(GetSymbolLoader(), typeArr, typeLst))
                {
                    return(false);
                }
                if (_needsExprDest)
                {
                    _binder.bindSimpleCast(_exprSrc, _exprTypeDest, out _exprDest, EXPRFLAG.EXF_REFCHECK);
                }
                return(true);
            }
Esempio n. 6
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            private bool bindImplicitConversionFromNullable(NullableType nubSrc)
            {
                // We can convert T? using a boxing conversion, we can convert it to ValueType, and
                // we can convert it to any interface implemented by T.
                //
                // 13.1.5 Boxing Conversions
                //
                // A nullable-type has a boxing conversion to the same set of types to which the nullable-type's
                // underlying type has boxing conversions. A boxing conversion applied to a value of a nullable-type
                // proceeds as follows:
                //
                // *   If the HasValue property of the nullable value evaluates to false, then the result of the
                //     boxing conversion is the null reference of the appropriate type.
                //
                // Otherwise, the result is obtained by boxing the result of evaluating the Value property on
                // the nullable value.

                AggregateType atsNub = nubSrc.GetAts();

                if (atsNub == _typeDest)
                {
                    if (_needsExprDest)
                    {
                        _exprDest = _exprSrc;
                    }
                    return(true);
                }
                if (GetSymbolLoader().HasBaseConversion(nubSrc.GetUnderlyingType(), _typeDest) && !CConversions.FUnwrappingConv(nubSrc, _typeDest))
                {
                    if (_needsExprDest)
                    {
                        _binder.bindSimpleCast(_exprSrc, _typeDest, out _exprDest, EXPRFLAG.EXF_BOX);
                        if (!_typeDest.isPredefType(PredefinedType.PT_OBJECT))
                        {
                            // The base type of a nullable is always a non-nullable value type,
                            // therefore so is typeDest unless typeDest is PT_OBJECT. In this case the conversion
                            // needs to be unboxed. We only need this if we actually will use the result.
                            _binder.bindSimpleCast(_exprDest, _typeDest, out _exprDest, EXPRFLAG.EXF_FORCE_UNBOX);
                        }
                    }
                    return(true);
                }
                return(0 == (_flags & CONVERTTYPE.NOUDC) && _binder.bindUserDefinedConversion(_exprSrc, nubSrc, _typeDest, _needsExprDest, out _exprDest, true));
            }
Esempio n. 7
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            /***************************************************************************************************
            *   Called by BindImplicitConversion when the destination type is Nullable<T>. The following
            *   conversions are handled by this method:
            *
            * For S in { object, ValueType, interfaces implemented by underlying type} there is an explicit
            *     unboxing conversion S => T?
            * System.Enum => T? there is an unboxing conversion if T is an enum type
            * null => T? implemented as default(T?)
            *
            * Implicit T?* => T?+ implemented by either wrapping or calling GetValueOrDefault the
            *     appropriate number of times.
            * If imp/exp S => T then imp/exp S => T?+ implemented by converting to T then wrapping the
            *     appropriate number of times.
            * If imp/exp S => T then imp/exp S?+ => T?+ implemented by calling GetValueOrDefault (m-1) times
            *     then calling HasValue, producing a null if it returns false, otherwise calling Value,
            *     converting to T then wrapping the appropriate number of times.
            *
            *   The 3 rules above can be summarized with the following recursive rules:
            *
            * If imp/exp S => T? then imp/exp S? => T? implemented as
            *     qs.HasValue ? (T?)(qs.Value) : default(T?)
            * If imp/exp S => T then imp/exp S => T? implemented as new T?((T)s)
            *
            *   This method also handles calling bindUserDefinedConverion. This method does NOT handle
            *   the following conversions:
            *
            * Implicit boxing conversion from S? to { object, ValueType, Enum, ifaces implemented by S }. (Handled by BindImplicitConversion.)
            * If imp/exp S => T then explicit S?+ => T implemented by calling Value the appropriate number
            *     of times. (Handled by BindExplicitConversion.)
            *
            *   The recursive equivalent is:
            *
            * If imp/exp S => T and T is not nullable then explicit S? => T implemented as qs.Value
            *
            *   Some nullable conversion are NOT standard conversions. In particular, if S => T is implicit
            *   then S? => T is not standard. Similarly if S => T is not implicit then S => T? is not standard.
            ***************************************************************************************************/
            private bool BindNubConversion(NullableType nubDst)
            {
                // This code assumes that STANDARD and ISEXPLICIT are never both set.
                // bindUserDefinedConversion should ensure this!
                Debug.Assert(0 != (~_flags & (CONVERTTYPE.STANDARD | CONVERTTYPE.ISEXPLICIT)));
                Debug.Assert(_exprSrc == null || _exprSrc.Type == _typeSrc);
                Debug.Assert(!_needsExprDest || _exprSrc != null);
                Debug.Assert(_typeSrc != nubDst); // BindImplicitConversion should have taken care of this already.
                AggregateType atsDst = nubDst.GetAts();

                // Check for the unboxing conversion. This takes precedence over the wrapping conversions.
                if (GetSymbolLoader().HasBaseConversion(nubDst.GetUnderlyingType(), _typeSrc) && !CConversions.FWrappingConv(_typeSrc, nubDst))
                {
                    // These should be different! Fix the caller if typeSrc is an AggregateType of Nullable.
                    Debug.Assert(atsDst != _typeSrc);

                    // typeSrc is a base type of the destination nullable type so there is an explicit
                    // unboxing conversion.
                    if (0 == (_flags & CONVERTTYPE.ISEXPLICIT))
                    {
                        return(false);
                    }

                    if (_needsExprDest)
                    {
                        _binder.bindSimpleCast(_exprSrc, _typeDest, out _exprDest, EXPRFLAG.EXF_UNBOX);
                    }
                    return(true);
                }

                bool           dstWasNullable;
                bool           srcWasNullable;
                CType          typeDstBase = nubDst.StripNubs(out dstWasNullable);
                CType          typeSrcBase = _typeSrc.StripNubs(out srcWasNullable);
                ConversionFunc pfn         = (_flags & CONVERTTYPE.ISEXPLICIT) != 0 ?
                                             (ConversionFunc)_binder.BindExplicitConversion :
                                             (ConversionFunc)_binder.BindImplicitConversion;

                if (!srcWasNullable)
                {
                    Debug.Assert(_typeSrc == typeSrcBase);

                    // The null type can be implicitly converted to T? as the default value.
                    if (_typeSrc is NullType)
                    {
                        // If we have the constant null, generate it as a default value of T?.  If we have
                        // some crazy expression which has been determined to be always null, like (null??null)
                        // keep it in its expression form and transform it in the nullable rewrite pass.
                        if (_needsExprDest)
                        {
                            if (_exprSrc.isCONSTANT_OK())
                            {
                                _exprDest = GetExprFactory().CreateZeroInit(nubDst);
                            }
                            else
                            {
                                _exprDest = GetExprFactory().CreateCast(_typeDest, _exprSrc);
                            }
                        }
                        return(true);
                    }

                    Expr exprTmp = _exprSrc;

                    // If there is an implicit/explicit S => T then there is an implicit/explicit S => T?
                    if (_typeSrc == typeDstBase || pfn(_exprSrc, _typeSrc, typeDstBase, _needsExprDest, out exprTmp, _flags | CONVERTTYPE.NOUDC))
                    {
                        if (_needsExprDest)
                        {
                            ExprUserDefinedConversion exprUDC = exprTmp as ExprUserDefinedConversion;
                            if (exprUDC != null)
                            {
                                exprTmp = exprUDC.UserDefinedCall;
                            }

                            if (dstWasNullable)
                            {
                                ExprCall call = _binder.BindNubNew(exprTmp);
                                exprTmp = call;
                                call.NullableCallLiftKind = NullableCallLiftKind.NullableConversionConstructor;
                            }

                            if (exprUDC != null)
                            {
                                exprUDC.UserDefinedCall = exprTmp;
                                exprTmp = exprUDC;
                            }

                            Debug.Assert(exprTmp.Type == nubDst);
                            _exprDest = exprTmp;
                        }
                        return(true);
                    }

                    // No builtin conversion. Maybe there is a user defined conversion....
                    return(0 == (_flags & CONVERTTYPE.NOUDC) && _binder.bindUserDefinedConversion(_exprSrc, _typeSrc, nubDst, _needsExprDest, out _exprDest, 0 == (_flags & CONVERTTYPE.ISEXPLICIT)));
                }

                // Both are Nullable so there is only a conversion if there is a conversion between the base types.
                // That is, if there is an implicit/explicit S => T then there is an implicit/explicit S?+ => T?+.
                if (typeSrcBase != typeDstBase && !pfn(null, typeSrcBase, typeDstBase, false, out _exprDest, _flags | CONVERTTYPE.NOUDC))
                {
                    // No builtin conversion. Maybe there is a user defined conversion....
                    return(0 == (_flags & CONVERTTYPE.NOUDC) && _binder.bindUserDefinedConversion(_exprSrc, _typeSrc, nubDst, _needsExprDest, out _exprDest, 0 == (_flags & CONVERTTYPE.ISEXPLICIT)));
                }

                if (_needsExprDest)
                {
                    MethWithInst    mwi       = new MethWithInst(null, null);
                    ExprMemberGroup pMemGroup = GetExprFactory().CreateMemGroup(null, mwi);
                    ExprCall        exprDst   = GetExprFactory().CreateCall(0, nubDst, _exprSrc, pMemGroup, null);

                    // Here we want to first check whether or not the conversions work on the base types.

                    Expr arg1        = _binder.mustCast(_exprSrc, typeSrcBase);
                    bool convertible = (_flags & CONVERTTYPE.ISEXPLICIT) != 0
                        ? _binder.BindExplicitConversion(
                        arg1, arg1.Type, typeDstBase, out arg1, _flags | CONVERTTYPE.NOUDC)
                        : _binder.BindImplicitConversion(
                        arg1, arg1.Type, typeDstBase, out arg1, _flags | CONVERTTYPE.NOUDC);

                    if (!convertible)
                    {
                        Debug.Fail("bind(Im|Ex)plicitConversion failed unexpectedly");
                        return(false);
                    }

                    exprDst.CastOfNonLiftedResultToLiftedType = _binder.mustCast(arg1, nubDst, 0);
                    exprDst.NullableCallLiftKind = NullableCallLiftKind.NullableConversion;
                    exprDst.PConversions         = exprDst.CastOfNonLiftedResultToLiftedType;
                    _exprDest = exprDst;
                }

                return(true);
            }
Esempio n. 8
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            /***************************************************************************************************
            *   Called by BindImplicitConversion when the destination type is Nullable<T>. The following
            *   conversions are handled by this method:
            *
            * For S in { object, ValueType, interfaces implemented by underlying type} there is an explicit
            *     unboxing conversion S => T?
            * System.Enum => T? there is an unboxing conversion if T is an enum type
            * null => T? implemented as default(T?)
            *
            * Implicit T?* => T?+ implemented by either wrapping or calling GetValueOrDefault the
            *     appropriate number of times.
            * If imp/exp S => T then imp/exp S => T?+ implemented by converting to T then wrapping the
            *     appropriate number of times.
            * If imp/exp S => T then imp/exp S?+ => T?+ implemented by calling GetValueOrDefault (m-1) times
            *     then calling HasValue, producing a null if it returns false, otherwise calling Value,
            *     converting to T then wrapping the appropriate number of times.
            *
            *   The 3 rules above can be summarized with the following recursive rules:
            *
            * If imp/exp S => T? then imp/exp S? => T? implemented as
            *     qs.HasValue ? (T?)(qs.Value) : default(T?)
            * If imp/exp S => T then imp/exp S => T? implemented as new T?((T)s)
            *
            *   This method also handles calling bindUserDefinedConverion. This method does NOT handle
            *   the following conversions:
            *
            * Implicit boxing conversion from S? to { object, ValueType, Enum, ifaces implemented by S }. (Handled by BindImplicitConversion.)
            * If imp/exp S => T then explicit S?+ => T implemented by calling Value the appropriate number
            *     of times. (Handled by BindExplicitConversion.)
            *
            *   The recursive equivalent is:
            *
            * If imp/exp S => T and T is not nullable then explicit S? => T implemented as qs.Value
            *
            *   Some nullable conversion are NOT standard conversions. In particular, if S => T is implicit
            *   then S? => T is not standard. Similarly if S => T is not implicit then S => T? is not standard.
            ***************************************************************************************************/
            private bool BindNubConversion(NullableType nubDst)
            {
                // This code assumes that STANDARD and ISEXPLICIT are never both set.
                // bindUserDefinedConversion should ensure this!
                Debug.Assert(0 != (~flags & (CONVERTTYPE.STANDARD | CONVERTTYPE.ISEXPLICIT)));
                Debug.Assert(exprSrc == null || exprSrc.type == typeSrc);
                Debug.Assert(!needsExprDest || exprSrc != null);
                Debug.Assert(typeSrc != nubDst); // BindImplicitConversion should have taken care of this already.
                AggregateType atsDst = nubDst.GetAts(GetErrorContext());

                if (atsDst == null)
                {
                    return(false);
                }

                // Check for the unboxing conversion. This takes precedence over the wrapping conversions.
                if (GetSymbolLoader().HasBaseConversion(nubDst.GetUnderlyingType(), typeSrc) && !CConversions.FWrappingConv(typeSrc, nubDst))
                {
                    // These should be different! Fix the caller if typeSrc is an AggregateType of Nullable.
                    Debug.Assert(atsDst != typeSrc);

                    // typeSrc is a base type of the destination nullable type so there is an explicit
                    // unboxing conversion.
                    if (0 == (flags & CONVERTTYPE.ISEXPLICIT))
                    {
                        return(false);
                    }

                    if (needsExprDest)
                    {
                        binder.bindSimpleCast(exprSrc, exprTypeDest, out exprDest, EXPRFLAG.EXF_UNBOX);
                    }
                    return(true);
                }

                int       cnubDst;
                int       cnubSrc;
                CType     typeDstBase     = nubDst.StripNubs(out cnubDst);
                EXPRCLASS exprTypeDstBase = GetExprFactory().MakeClass(typeDstBase);
                CType     typeSrcBase     = typeSrc.StripNubs(out cnubSrc);

                ConversionFunc pfn = (flags & CONVERTTYPE.ISEXPLICIT) != 0 ?
                                     (ConversionFunc)binder.BindExplicitConversion :
                                     (ConversionFunc)binder.BindImplicitConversion;

                if (cnubSrc == 0)
                {
                    Debug.Assert(typeSrc == typeSrcBase);

                    // The null type can be implicitly converted to T? as the default value.
                    if (typeSrc.IsNullType())
                    {
                        // If we have the constant null, generate it as a default value of T?.  If we have
                        // some crazy expression which has been determined to be always null, like (null??null)
                        // keep it in its expression form and transform it in the nullable rewrite pass.
                        if (needsExprDest)
                        {
                            if (exprSrc.isCONSTANT_OK())
                            {
                                exprDest = GetExprFactory().CreateZeroInit(nubDst);
                            }
                            else
                            {
                                exprDest = GetExprFactory().CreateCast(0x00, typeDest, exprSrc);
                            }
                        }
                        return(true);
                    }

                    EXPR exprTmp = exprSrc;

                    // If there is an implicit/explicit S => T then there is an implicit/explicit S => T?
                    if (typeSrc == typeDstBase || pfn(exprSrc, typeSrc, exprTypeDstBase, nubDst, needsExprDest, out exprTmp, flags | CONVERTTYPE.NOUDC))
                    {
                        if (needsExprDest)
                        {
                            // UNDONE: This is a premature realization of the nullable conversion as
                            // UNDONE: a constructor.  Rather than flagging this, can we simply emit it
                            // UNDONE: as a cast node and have the operator rewrite pass turn it into
                            // UNDONE: a constructor call?
                            EXPRUSERDEFINEDCONVERSION exprUDC = exprTmp.kind == ExpressionKind.EK_USERDEFINEDCONVERSION ? exprTmp.asUSERDEFINEDCONVERSION() : null;
                            if (exprUDC != null)
                            {
                                exprTmp = exprUDC.UserDefinedCall;
                            }

                            // This logic is left over from the days when T?? was legal. However there are error/LAF cases that necessitates the loop.
                            // typeSrc is not nullable so just wrap the required number of times. For legal code (cnubDst <= 0).

                            for (int i = 0; i < cnubDst; i++)
                            {
                                exprTmp = binder.BindNubNew(exprTmp);
                                exprTmp.asCALL().nubLiftKind = NullableCallLiftKind.NullableConversionConstructor;
                            }
                            if (exprUDC != null)
                            {
                                exprUDC.UserDefinedCall = exprTmp;
                                exprUDC.setType((CType)exprTmp.type);
                                exprTmp = exprUDC;
                            }
                            Debug.Assert(exprTmp.type == nubDst);
                            exprDest = exprTmp;
                        }
                        return(true);
                    }

                    // No builtin conversion. Maybe there is a user defined conversion....
                    return(0 == (flags & CONVERTTYPE.NOUDC) && binder.bindUserDefinedConversion(exprSrc, typeSrc, nubDst, needsExprDest, out exprDest, 0 == (flags & CONVERTTYPE.ISEXPLICIT)));
                }

                // Both are Nullable so there is only a conversion if there is a conversion between the base types.
                // That is, if there is an implicit/explicit S => T then there is an implicit/explicit S?+ => T?+.
                if (typeSrcBase != typeDstBase && !pfn(null, typeSrcBase, exprTypeDstBase, nubDst, false, out exprDest, flags | CONVERTTYPE.NOUDC))
                {
                    // No builtin conversion. Maybe there is a user defined conversion....
                    return(0 == (flags & CONVERTTYPE.NOUDC) && binder.bindUserDefinedConversion(exprSrc, typeSrc, nubDst, needsExprDest, out exprDest, 0 == (flags & CONVERTTYPE.ISEXPLICIT)));
                }

                if (needsExprDest)
                {
                    MethWithInst mwi       = new MethWithInst(null, null);
                    EXPRMEMGRP   pMemGroup = GetExprFactory().CreateMemGroup(null, mwi);
                    EXPRCALL     exprDst   = GetExprFactory().CreateCall(0, nubDst, exprSrc, pMemGroup, null);

                    // Here we want to first check whether or not the conversions work on the base types.

                    EXPR      arg1 = binder.mustCast(exprSrc, typeSrcBase);
                    EXPRCLASS arg2 = GetExprFactory().MakeClass(typeDstBase);

                    bool convertible;
                    if (0 != (flags & CONVERTTYPE.ISEXPLICIT))
                    {
                        convertible = binder.BindExplicitConversion(arg1, arg1.type, arg2, typeDstBase, out arg1, flags | CONVERTTYPE.NOUDC);
                    }
                    else
                    {
                        convertible = binder.BindImplicitConversion(arg1, arg1.type, arg2, typeDstBase, out arg1, flags | CONVERTTYPE.NOUDC);
                    }
                    if (!convertible)
                    {
                        VSFAIL("bind(Im|Ex)plicitConversion failed unexpectedly");
                        return(false);
                    }

                    exprDst.castOfNonLiftedResultToLiftedType = binder.mustCast(arg1, nubDst, 0);
                    exprDst.nubLiftKind  = NullableCallLiftKind.NullableConversion;
                    exprDst.pConversions = exprDst.castOfNonLiftedResultToLiftedType;
                    exprDest             = exprDst;
                }

                return(true);
            }