VBA: These blog posts cover hard topics on working with array formulas in Excel

Many thanks to two great blogs RAD Excel and Daily Dose of Excel for covering hard topic on working with array formulas and setting long array formulas for the Range objects in Excel.

VBA: Run-time error 3001 Arguments Are Of The Wrong Type... when setting ADODB.Command object members

This forum post saved my day.
I was trying to run Oracle stored procedure with output parameters from Excel VBA with the following piece of code:

Dim cmd As Object
Dim resultSet As Object
Set cmd = CreateObject("ADODB.Command")
With cmd
    .CommandText = "PK_AUTH.LOGON"    
    .NamedParameters = True
    .Parameters.Append .CreateParameter("login", adVarChar, adParamInput, 50, login_)
    .Parameters.Append .CreateParameter("pass", adVarChar, adParamInput, 50, pass_)
    .Parameters.Append .CreateParameter("ldb", adVarChar, adParamOutput, 50)
    .Parameters.Append .CreateParameter("pdb", adVarChar, adParamOutput, 50)
    .CommandType = adCmdStoredProc
    .ActiveConnection = GetConn_()
    Set resultSet = .Execute
    ldb_ = .Parameters.Item("ldb")
End With

And I always got Run-time error 3001 'Arguments Are Of The Wrong Type, Are Out Of The Acceptable Range, or are in conflict with one another' upon invocation of

.CommandType = adCmdStoredProc

or

.Parameters.Append .CreateParameter(...)

no matter which statement I placed first.
After fighting for a while I found this post that stated that error is fired because of late binding of library references, so VB simply did not know of adCmdStoredProc and other constants
That meant that this error has nothing to do with ADODB or Ole or, I just said that it does not know the value of constant. Not very informative in fact...
So, I simply added

Const adVarChar As Long = 200
Const adParamInput As Long = &H1
Const adParamOutput As Long = &H2
Const adCmdStoredProc As Long = &H4

to the Sub header and everything worked fine. Constants are defined in c:\Program Files\Common Files\System\ado\adovbs.inc

VBA: Prototype Class than connects to oracle and checks if connection is up. Plus VBA singleton pattern

Here some prototyping code of a class that is able to connect to Oracle through OleDB and to check if the connection is up before doing some application logic. Class name is TUploadHelper.

Private m_conn As Object

Private Function GetConn_() As Object
    If m_conn Is Nothing Then
        Set m_conn = CreateObject("ADODB.Connection")
    End If
    Set GetConn_ = m_conn
End Function

Private Function Connected_() As Boolean
    Dim recordSet As Object
    Dim value As Long
    Dim errCode As Variant
    Dim errMsg As Variant

    If Not PopErrors() Then On Error GoTo L_ERR_HANDLER
    
    value = 0
    Connected_ = False
    
    Set recordSet = CreateObject("ADODB.Recordset")
    
    Set recordSet.ActiveConnection = GetConn_()
    
    recordSet.Open "select 1 as value_ from dual"
    While Not recordSet.EOF
        value = recordSet.Fields(0)
        If 1 = value Then
            Connected_ = True
            GoTo L_CLEANUP
        End If
    Wend
    ' не вернулось ни одной записи
L_ERR_HANDLER:
    errCode = Err.Number
    errMsg = Err.Description
L_CLEANUP:
    On Error GoTo 0
    If 1 = recordSet.State Then
        recordSet.Close
    End If
    Set recordSet = Nothing
End Function


Private Sub Class_Deinitialize()
    If Not m_conn Is Nothing Then
        If 1 = m_conn.State Then
            m_conn.Close
        End If
        Set m_conn = Nothing
    End If
End Sub

Private Function Authorized_() As Boolean
    Authorized_ = False
End Function

Private Sub Connect_()
'    Dim state_ As Variant
    m_conn.Open "Provider=OraOLEDB.Oracle;Data Source=your_server.world;User ID=your_user;Password=your_pass;PLSQLRSet=1;"
'    state_ = m_conn.State
End Sub

Public Sub Ut()
    If Not Connected_ Then
        Connect_
        If Not Connected_ Then
        End If
    End If
End Sub

And here is module code that implements singleton pattern for TUploadHelper object.

'Singleton pattern
Private g_uploadHelper As TUploadHelper
Public Property Get GetUploadHelper() As TUploadHelper
    If g_uploadHelper Is Nothing Then
        Set g_uploadHelper = New TUploadHelper
    End If
    Set GetUploadHelper = g_uploadHelper
End Property