Option Explicit
Private mlngCapacity As Long ''''缓冲区的当前容量,可用于插入新的字符的存储空间
Private mlngLength As Long ''''字符个数
Private mlngEOA As Long ''''数组第一个空元素的索引
Private mabyt() As Byte
Private mlngUb As Long ''''数组上界

Private Sub Class_Initialize()
    mlngCapacity = 2048
    ReDim mabyt(4095)
End Sub

Private Sub Class_Terminate()
    Erase mabyt
End Sub

Public Sub append(ByVal str As String)
    Dim abyt() As Byte ''''添加的字符串转为Byte数组
    Dim lngUb As Long ''''添加的字符串转为Byte数组的上界
    Dim lngLength As Long ''''添加的字符串的长度
    Dim i As Long
    abyt = str
    lngUb = UBound(abyt)
    lngLength = (lngUb + 1) \ 2
    Do While lngLength > mlngCapacity ''''插入新的字符超出缓冲区容量
        mlngUb = mlngUb + 4096
        ReDim mabyt(mlngUb) ''''缓冲区扩容
        mlngCapacity = mlngCapacity + 2048
    Loop
    For i = 0 To lngUb
        mabyt(mlngEOA + i) = abyt(i)
    Next
    mlngEOA = mlngEOA + lngUb + 1
    mlngCapacity = mlngCapacity - lngLength
    mlngLength = mlngLength + lngLength
    Erase abyt
End Sub

Public Property Get length() As Long
    length = mlngLength
End Property

Public Property Get capacity() As Long
    capacity = mlngCapacity
End Property

Public Function toString() As String
    ReDim Preserve mabyt(mlngEOA - 1)
    toString = mabyt
    ReDim Preserve mabyt(mlngUb)
End Function