Refactor Scoped Variable To Parameter

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