cachedexpression.vb

大名鼎鼎的mono是.NET平台的跨平台（支持linux

' 
' Visual Basic.Net Compiler
' Copyright (C) 2004 - 2007 Rolf Bjarne Kvinge, [e-mail]
' 
' This library is free software; you can redistribute it and/or
' modify it under the terms of the GNU Lesser General Public
' License as published by the Free Software Foundation; either
' version 2.1 of the License, or (at your option) any later version.
' 
' This library is distributed in the hope that it will be useful,
' but WITHOUT ANY WARRANTY; without even the implied warranty of
' MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
' Lesser General Public License for more details.
' 
' You should have received a copy of the GNU Lesser General Public
' License along with this library; if not, write to the Free Software
' Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
' 
Public Class CachedExpression
    Inherits Expression

    Private m_Expression As Expression

    Private m_Local As LocalBuilder

    Sub New(ByVal Parent As Expression, ByVal Expression As Expression)
        MyBase.new(Parent)
        m_Expression = Expression
    End Sub

    Protected Overrides Function GenerateCodeInternal(ByVal Info As EmitInfo) As Boolean
        Dim result As Boolean = True

        If m_Local Is Nothing Then
            result = m_Expression.GenerateCode(Info.Clone(True, False, m_Expression.ExpressionType)) AndAlso result
            m_Local = Emitter.DeclareLocal(Info, m_Expression.ExpressionType)
            Emitter.EmitStoreVariable(Info, m_Local)
        End If

        Emitter.EmitLoadVariable(Info, m_Local)

        Return result
    End Function

    Overrides ReadOnly Property ExpressionType() As Type
        Get
            Return m_Expression.ExpressionType
        End Get
    End Property

    Public Overrides ReadOnly Property IsConstant() As Boolean
        Get
            Return False
        End Get
    End Property

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

        If m_Expression.IsResolved = False Then
            result = m_Expression.ResolveExpression(Info)
        Else
            result = True
        End If

        Classification = New ValueClassification(Me, Me.ExpressionType)

        Return result
    End Function
End Class