ctypeexpression.vb

大名鼎鼎的mono是.NET平台的跨平台（支持linux

                If Helper.CompareType(Compiler.TypeCache.System_Object, SourceElementType) Then
                    Emitter.EmitCastClass(Info, SourceType, DestinationType)
                ElseIf Helper.CompareType(SourceElementType, DestinationElementType) OrElse DestinationElementType.IsSubclassOf(SourceElementType) OrElse SourceElementType.IsSubclassOf(DestinationElementType) Then
                    Emitter.EmitCastClass(Info, SourceType, DestinationType)
                ElseIf Helper.DoesTypeImplementInterface(Compiler, SourceElementType, DestinationElementType) Then
                    Emitter.EmitCastClass(Info, SourceType, DestinationType)
                ElseIf DestinationElementType.IsInterface AndAlso Helper.CompareType(Compiler.TypeCache.System_Object, SourceElementType) Then
                    Emitter.EmitCastClass(Info, SourceType, DestinationType)
                ElseIf SourceElementType.IsEnum AndAlso Helper.CompareType(Helper.GetEnumType(Compiler, SourceElementType), DestinationElementType) Then
                    'Conversions also exist between an array of an enumerated type and an array of the enumerated type's underlying type of the same rank.
                    Emitter.EmitCastClass(Info, SourceType, DestinationType)
                ElseIf TypeOf SourceElementType Is TypeParameterDescriptor AndAlso Helper.IsTypeConvertibleToAny(Helper.GetGenericParameterConstraints(SourceElementType), DestinationElementType) Then
                    Emitter.EmitCastClass(Info, SourceType, DestinationType)
                Else
                    Info.Compiler.Report.ShowMessage(Messages.VBNC30311, SourceType.Name, DestinationType.Name)
                    result = False
                End If

            End If
        ElseIf SourceType.IsClass Then
            If DestinationType.IsGenericParameter Then
                Dim method As MethodInfo
                method = Compiler.TypeCache.MS_VB_CS_Conversions__ToGenericParameter_Object.MakeGenericMethod(DestinationType.UnderlyingSystemType)

                Emitter.EmitCall(Info, Compiler.TypeCache.System_Runtime_CompilerServices_RuntimeHelpers__GetObjectValue_Object)
                Emitter.EmitCall(Info, method)
            ElseIf DestinationType.IsClass Then
                Emitter.EmitCastClass(Info, SourceType, DestinationType)
            ElseIf DestinationType.IsInterface Then
                Emitter.EmitCastClass(Info, SourceType, DestinationType)
            ElseIf DestinationType.IsValueType Then
                Emitter.EmitUnbox(Info, DestinationType)
                Emitter.EmitLdobj(Info, DestinationType)
            ElseIf DestinationType.IsEnum Then
                Throw New InternalException(Me) 'This is an elemental conversion already covered.
            ElseIf DestinationType.IsArray Then
                Throw New InternalException(Me) 'This is an IsClass case.
            Else
                Throw New InternalException(Me)
            End If
        ElseIf SourceType.IsValueType Then
            'A value type value can be converted to one of its base reference types or an interface type that it implements through a process called boxing
            If Helper.CompareType(DestinationType, Compiler.TypeCache.System_Object) Then
                Throw New InternalException(Me) 'This is an elemental conversion already covered. 'Emitter.EmitBox(Info)
            ElseIf Helper.DoesTypeImplementInterface(Compiler, SourceType, DestinationType) Then
                Emitter.EmitBox(Info, SourceType)
                Emitter.EmitCastClass(Info, Compiler.TypeCache.System_Object, DestinationType)
            ElseIf Helper.CompareType(SourceType.BaseType, DestinationType) Then
                Emitter.EmitBox(Info, DestinationType)
            Else
                Throw New InternalException("Operator CType is not defined for types '" & SourceType.FullName & "' and '" & DestinationType.FullName & "'")
            End If
        ElseIf SourceType.IsInterface Then
            If DestinationType.IsGenericParameter Then
                Dim method As MethodInfo
                method = Compiler.TypeCache.MS_VB_CS_Conversions__ToGenericParameter_Object.MakeGenericMethod(DestinationType.UnderlyingSystemType)

                Emitter.EmitCall(Info, Compiler.TypeCache.System_Runtime_CompilerServices_RuntimeHelpers__GetObjectValue_Object)
                Emitter.EmitCall(Info, method)
            ElseIf Helper.DoesTypeImplementInterface(Compiler, DestinationType, SourceType) Then
                If DestinationType.IsValueType Then
                    Emitter.EmitUnbox(Info, DestinationType)
                    Emitter.EmitLdobj(Info, DestinationType)
                Else
                    Emitter.EmitCastClass(Info, SourceType, DestinationType)
                End If

            ElseIf DestinationType.IsClass OrElse DestinationType.IsInterface Then
                Emitter.EmitCastClass(Info, SourceType, DestinationType)
            Else
                'However, classes that represent COM classes may have interface implementations that are not known until run time. Consequently, a class type may also be converted to an interface type that it does not implement, an interface type may be converted to a class type that does not implement it, and an interface type may be converted to another interface type with which it has no inheritance relationship
                Helper.NotImplemented()
            End If
        Else
            Helper.NotImplemented()
        End If

        Return result
    End Function

    Protected Overrides Function ResolveExpressionInternal(ByVal Info As ResolveInfo) As Boolean
        Dim result As Boolean = True

        If m_ResolvedDestinationType Is Nothing Then
            result = m_DestinationType.ResolveTypeReferences AndAlso result
            m_ResolvedDestinationType = m_DestinationType.ResolvedType
        End If

        result = MyBase.ResolveExpressionInternal(Info) AndAlso result

        Select Case Helper.GetTypeCode(Compiler, Me.ExpressionType)
            Case TypeCode.Boolean
                result = CBoolExpression.Validate(Info, Expression.ExpressionType) AndAlso result
            Case TypeCode.Byte
                result = CByteExpression.Validate(Info, Expression.ExpressionType) AndAlso result
            Case TypeCode.Char
                result = CCharExpression.Validate(Info, Expression.ExpressionType) AndAlso result
            Case TypeCode.DateTime
                result = CDateExpression.Validate(Info, Expression.ExpressionType) AndAlso result
            Case TypeCode.Decimal
                result = CDecExpression.Validate(Info, Expression.ExpressionType) AndAlso result
            Case TypeCode.Double
                result = CDblExpression.Validate(Info, Expression.ExpressionType) AndAlso result
            Case TypeCode.Int16
                result = CShortExpression.Validate(Info, Expression.ExpressionType) AndAlso result
            Case TypeCode.Int32
                result = CIntExpression.Validate(Info, Expression.ExpressionType) AndAlso result
            Case TypeCode.Int64
                result = CLngExpression.Validate(Info, Expression.ExpressionType) AndAlso result
            Case TypeCode.SByte
                result = CSByteExpression.Validate(Info, Expression.ExpressionType) AndAlso result
            Case TypeCode.Single
                result = CSngExpression.Validate(Info, Expression.ExpressionType) AndAlso result
            Case TypeCode.String
                result = CStrExpression.Validate(Info, Expression.ExpressionType) AndAlso result
            Case TypeCode.UInt16
                result = CUShortExpression.Validate(Info, Expression.ExpressionType) AndAlso result
            Case TypeCode.UInt32
                result = CUIntExpression.Validate(Info, Expression.ExpressionType) AndAlso result
            Case TypeCode.UInt64
                result = CULngExpression.Validate(Info, Expression.ExpressionType) AndAlso result
            Case TypeCode.Object, TypeCode.DBNull
                If Helper.CompareType(Me.ExpressionType, Compiler.TypeCache.System_Object) Then
                    result = CObjExpression.Validate(Info, Expression.ExpressionType) AndAlso result
                ElseIf Helper.CompareType(Me.ExpressionType, Compiler.TypeCache.System_Char_Array) AndAlso Helper.CompareType(Expression.ExpressionType, Compiler.TypeCache.System_String) Then
                    If Location.File(Compiler).IsOptionStrictOn Then
                        result = Compiler.Report.ShowMessage(Messages.VBNC30512, Location, Expression.ExpressionType.FullName, Me.ExpressionType.FullName)
                    Else
                        m_IsStringToCharArray = True
                    End If
                Else
                    'Helper.NotImplementedYet("") Anything to do here?
                End If
            Case Else
                Throw New InternalException(Me)
        End Select

        Return result


        Return result
    End Function

    Overrides ReadOnly Property ExpressionType() As Type
        Get
            Return m_ResolvedDestinationType
        End Get
    End Property

    Public Overrides ReadOnly Property ConstantValue() As Object
        Get
            Select Case Helper.GetTypeCode(Compiler, Me.ExpressionType)
                Case TypeCode.String
                    Select Case Helper.GetTypeCode(Compiler, Me.Expression.ExpressionType)
                        Case TypeCode.Char
                            Return CStr(Expression.ConstantValue)
                        Case Else
                            Helper.NotImplemented()
                            Throw New InternalException(Me)
                    End Select
                Case Else
                    Helper.NotImplemented()
                    Throw New InternalException(Me)
            End Select
        End Get
    End Property

    Public Overrides ReadOnly Property IsConstant() As Boolean
        Get
            If Expression.IsConstant Then
                If m_ResolvedDestinationType IsNot Nothing AndAlso Helper.CompareType(m_ResolvedDestinationType, Compiler.TypeCache.System_String) AndAlso Helper.CompareType(Expression.ExpressionType, Compiler.TypeCache.System_Char) Then
                    Return True
                Else
                    Return False
                End If
            Else
                Return False
            End If
            Return False 'TODO: This isn't true.
        End Get
    End Property

    Protected Overridable ReadOnly Property GetKeyword() As KS
        Get
            Return KS.CType
        End Get
    End Property

#If DEBUG Then
    Public Overrides Sub Dump(ByVal Dumper As IndentedTextWriter)
        Dumper.Write(Enums.GetKSStringAttribute(GetKeyword).FriendlyValue)
        Dumper.Write("(")
        Expression.Dump(Dumper)
        Dumper.Write(" ,")
        Compiler.Dumper.Dump(m_DestinationType)
        Dumper.Write(")")
    End Sub
#End If
End Class