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.)

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

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?

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.

Opposite of RefactorParametersToMemberVariables

CategoryRefactoring, RefactoringLanguage