Global variables are bad.


Module-level scoping isn't that much better (IE: form-level in VB, source-file-level in C/C++).

Sometimes the best way to reduce coupling is to just pass functions/methods the data they need, as parameters.

''(However, if you make a habit of this, you may later find that you need to RefactorParametersToMemberVariables, to build well-formed classes.)''

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Needs examples. Generally, I'd stay away from this. When is it useful?

''Most obvious example typically occurs in bloated classes -- those that have too many member variables and methods.  VisualBasic forms often fall into this category.  By changing methods from "access variable from enclosing scope" to "accept variable as a parameter," one reduces coupling.  This enables refactoring the method out to a function library or off into another class.''

Before:
  Form:
  Dim moConn As ADODB.Connection
  Private Function SelectCustomerStuff(ByVal iAmAParm as Integer) As ADODB.Recordset
     ' <lots of stuff, including a SELECT statement using 'moConn' variable>
  End Function
After:
  Form:
  Dim moConn As ADODB.Connection
  Private Function SelectCustomerStuff('''ByVal oConn As ADODB.Connection,''' ByVal iAmAParm as Integer) As ADODB.Recordset
     ' <lots of stuff, including a SELECT statement using 'oConn' variable>
  End Function
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I see where you're going now. How about this progression?

Start:
  Form
    Dim moConn As ADODB.Connection
    Private Function SelectCustomerStuff(ByVal iAmAParm as Integer) As ADODB.Recordset
      ...
      Set SelectCustomerStuff = '''moConn'''.Execute("SELECT * ...")
      ...
    End Function
     
    Private Sub Form_Load()
      Dim rs As ADODB.Recordset
      Set rs = '''SelectCustomerStuff(8)'''
    End Sub

Next:
  Form
    Dim moConn As ADODB.Connection
    Private Function SelectCustomerStuff('''ByVal oConn As ADODB.Connection,''' ByVal iAmAParm as Integer) As ADODB.Recordset
      ...
      Set SelectCustomerStuff = '''oConn'''.Execute("SELECT * ...")
      ...
    End Function

    Private Sub Form_Load()
      Dim rs As ADODB.Recordset
      Set rs = '''SelectCustomerStuff(moConn, 8)'''
    End Sub

Next:
  Form
    Dim moConn As ADODB.Connection
    Private Sub Form_Load()
      Dim rs As ADODB.Recordset
      '''Dim o as Class'''
      '''Set o = new Class'''
      Set rs = '''o.SelectCustomerStuff(moConn, 8)'''
    End Sub

  '''Class'''
    '''Public''' Function SelectCustomerStuff(ByVal oConn As ADODB.Connection, ByVal iAmAParm as Integer) As ADODB.Recordset
      ...
      Set SelectCustomerStuff = oConn.Execute("SELECT * ...")
      ...
    End Function

Next (Now we can apply RefactorParametersToMemberVariables):
  Form
    Dim moConn As ADODB.Connection
    Private Sub Form_Load()
      Dim rs As ADODB.Recordset
      Dim o as Class
      Set o = new Class
      '''o.Init(moConn)'''
      Set rs = '''o.SelectCustomerStuff(8)'''
    End Sub

  Class
    Private moConn as ADODB.Connection

    Public Function SelectCustomerStuff'''(ByVal iAmAParm as Integer)''' As ADODB.Recordset
      ...
      Set SelectCustomerStuff = '''moConn'''.Execute("SELECT * ...")
      ...
    End Function

Etc. Until you can finally move moConn out of the form. Is that the general idea? Maybe there's a more direct route.

What about a combination of MoveField and MoveMethod?

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Actually, I had in mind something like this...

Start:
  Form 1:
    Dim moConn As ADODB.Connection
    Private Sub Form_Load()
      Dim rs As ADODB.Recordset
      '''Set moConn = ConnectToAdoDatabase()'''
      Set rs = SelectCustomerStuff(8)
    End Sub
    Private Function SelectCustomerStuff(ByVal iAmAParm as Integer) As ADODB.Recordset
      ...  Set SelectCustomerStuff = moConn.Execute("SELECT * ...")  ...
    End Function

to maybe...
  Form 1:
    Dim moConn As ADODB.Connection
    Private Sub Form_Load()
      Dim rs As ADODB.Recordset
      Set moConn = ConnectToAdoDatabase()
      Set rs = SelectCustomerStuff('''moConn,''' 8)
    End Sub
  '''Module 2:'''
    Private Function SelectCustomerStuff('''ByVal oConn As ADODB.Connection,''' ByVal iAmAParm as Integer) As ADODB.Recordset
      ...  Set SelectCustomerStuff = moConn.Execute("SELECT * ...")  ...
    End Function

But there's something to be said for putting all the SQL in a class.
(It helps you get to MockObject, for instance.)
  Form 1:
    Private Sub Form_Load()
      Dim rs As ADODB.Recordset
      '''Dim oSql As New FormSql'''
      Set rs = '''oSql.'''SelectCustomerStuff(8)
    End Sub
  '''Class FormSql:'''
    Dim moConn As ADODB.Connection
    Private Sub Class_Initialize
      Set moConn = ConnectToAdoDatabase()
    End Sub
    Private Function SelectCustomerStuff(ByVal iAmAParm as Integer) As ADODB.Recordset
      ...  Set SelectCustomerStuff = moConn.Execute("SELECT * ...")  ...
    End Function
''But that's really a different refactoring.''

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Opposite of RefactorParametersToMemberVariables
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CategoryRefactoring, RefactoringLanguage