Private Declare Function GetTickCount Lib "kernel32" () As Int32
    Private Function TestByRef(ByRef aa As String) As String
        aa = "1" aa
        TestByRef = aa
    End Function
    Private Function TestByVal(ByVal aa As String) As String
        aa = "1" aa
        TestByVal = aa
    End Function
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim teststr As String
        Dim Newstr As String
        Dim t As Int32
        Dim II As Int32
        teststr = "wosdfsdfdsfdsfsfdsfsfsfsfsfsfdsfdsfcvxcvxcvcxvvcxvvvxvcvxv"
        t = GetTickCount
        For II = 1 To 10000
            Newstr = TestByRef(teststr)
        Next
        MsgBox("ByRef  " CStr(GetTickCount - t))
        t = GetTickCount
        For II = 1 To 10000
            Newstr = TestByVal(teststr)
        Next
        MsgBox("ByVal  " CStr(GetTickCount - t))
    End Sub