Passing methods as parameters - c++11

Question

I have reviewed this excellent answer but I am still confused. Ultimately I will have 10 method all behaving similar. Here is an example of three I have written already:
void CChristianLifeMinistryEditorDlg::OnSwapWithChairmanAssignment(UINT nID)
{
// We need to locate the name for this assignment
auto iter = m_mapSwapAssignments.find(nID);
if (iter != m_mapSwapAssignments.end())
{
// We found it
CChristianLifeMinistryEntry *pReplacement = m_mapSwapAssignments[nID];
CString strExistingName = _T(""), strReplacementName = _T("");
GetDlgItemText(m_iSwapAssignmentSourceID, strExistingName);
CString strPrompt = _T("");
strPrompt.Format(_T("Swap assignments:\n\n%s - %s\n%s - %s\n\nPlease confirm."),
m_pEntry->GetMeetingDateAsString(),
(LPCTSTR)strExistingName,
pReplacement->GetMeetingDateAsString(),
(LPCTSTR)pReplacement->GetChairman());
if (AfxMessageBox(strPrompt, MB_ICONQUESTION | MB_YESNO) == IDYES)
{
strReplacementName = pReplacement->GetChairman();
pReplacement->SetChairman(strExistingName);
SetDlgItemText(m_iSwapAssignmentSourceID, strReplacementName);
SetModified(true);
}
}
}
void CChristianLifeMinistryEditorDlg::OnSwapWithOpenPrayerAssignment(UINT nID)
{
// We need to locate the name for this assignment
auto iter = m_mapSwapAssignments.find(nID);
if (iter != m_mapSwapAssignments.end())
{
// We found it
CChristianLifeMinistryEntry *pReplacement = m_mapSwapAssignments[nID];
CString strExistingName = _T(""), strReplacementName = _T("");
GetDlgItemText(m_iSwapAssignmentSourceID, strExistingName);
CString strPrompt = _T("");
strPrompt.Format(_T("Swap assignments:\n\n%s - %s\n%s - %s\n\nPlease confirm."),
m_pEntry->GetMeetingDateAsString(),
(LPCTSTR)strExistingName,
pReplacement->GetMeetingDateAsString(),
(LPCTSTR)pReplacement->GetOpenPrayer());
if (AfxMessageBox(strPrompt, MB_ICONQUESTION | MB_YESNO) == IDYES)
{
strReplacementName = pReplacement->GetOpenPrayer();
pReplacement->SetOpenPrayer(strExistingName);
SetDlgItemText(m_iSwapAssignmentSourceID, strReplacementName);
SetModified(true);
}
}
}
void CChristianLifeMinistryEditorDlg::OnSwapWithClosePrayerAssignment(UINT nID)
{
// We need to locate the name for this assignment
auto iter = m_mapSwapAssignments.find(nID);
if (iter != m_mapSwapAssignments.end())
{
// We found it
CChristianLifeMinistryEntry *pReplacement = m_mapSwapAssignments[nID];
CString strExistingName = _T(""), strReplacementName = _T("");
GetDlgItemText(m_iSwapAssignmentSourceID, strExistingName);
CString strPrompt = _T("");
strPrompt.Format(_T("Swap assignments:\n\n%s - %s\n%s - %s\n\nPlease confirm."),
m_pEntry->GetMeetingDateAsString(),
(LPCTSTR)strExistingName,
pReplacement->GetMeetingDateAsString(),
(LPCTSTR)pReplacement->GetClosePrayer());
if (AfxMessageBox(strPrompt, MB_ICONQUESTION | MB_YESNO) == IDYES)
{
strReplacementName = pReplacement->GetClosePrayer();
pReplacement->SetClosePrayer(strExistingName);
SetDlgItemText(m_iSwapAssignmentSourceID, strReplacementName);
SetModified(true);
}
}
}
I want to code the code from each of those event handlers into a method.
GetChairman
SetChairman
GetOpenPrayer
SetOpenPrayer
GetClosePrayer
SetClosePrayer
I have tried this:
void CChristianLifeMinistryEditorDlg::SwapAssignments(UINT nID, CString(*GetExistingName), void(*SetReplacementName)(CString))
{
// We need to locate the name for this assignment
auto iter = m_mapSwapAssignments.find(nID);
if (iter != m_mapSwapAssignments.end())
{
// We found it
CChristianLifeMinistryEntry *pReplacement = m_mapSwapAssignments[nID];
CString strExistingName = _T(""), strReplacementName = _T("");
GetDlgItemText(m_iSwapAssignmentSourceID, strExistingName);
CString strPrompt = _T("");
strPrompt.Format(_T("Swap assignments:\n\n%s - %s\n%s - %s\n\nPlease confirm."),
m_pEntry->GetMeetingDateAsString(),
(LPCTSTR)strExistingName,
pReplacement->GetMeetingDateAsString(),
(LPCTSTR)pReplacement->(*GetExistingName));
if (AfxMessageBox(strPrompt, MB_ICONQUESTION | MB_YESNO) == IDYES)
{
strReplacementName = pReplacement->(*GetExistingName);
pReplacement->(*SetReplacementName)(strExistingName);
SetDlgItemText(m_iSwapAssignmentSourceID, strReplacementName);
SetModified(true);
}
}
}
I get build errors:
How can pass these methods as parameters?
I see this other answer that I was hoping I could use but the problem is that the method being called is a member of an object. So it won't allow it.
Current Workaround
At the moment I have implemented a couple of functions:
CString CChristianLifeMinistryEntry::GetName(SwapAssignment eAssignment)
{
switch (eAssignment)
{
case SwapAssignment::Chairman:
return GetChairman();
case SwapAssignment::Counsellor1:
return GetAuxiliaryCounsellor1();
case SwapAssignment::Counsellor2:
return GetAuxiliaryCounsellor2();
case SwapAssignment::OpenPrayer:
return GetOpenPrayer();
case SwapAssignment::Treasures1:
return GetTreasures1();
case SwapAssignment::Treasures2:
return GetTreasures2();
case SwapAssignment::Living1:
return GetLiving1();
case SwapAssignment::Living2:
return GetLiving2();
case SwapAssignment::ConductorCBS:
return GetCBSConductor();
case SwapAssignment::ReaderCBS:
return GetCBSReader();
case SwapAssignment::ClosePrayer:
return GetClosePrayer();
}
return _T("");
}
// AJT v18.1.6
void CChristianLifeMinistryEntry::SetName(CString strName, SwapAssignment eAssignment)
{
switch (eAssignment)
{
case SwapAssignment::Chairman:
SetChairman(strName);
break;
case SwapAssignment::Counsellor1:
SetAuxiliaryCounsellor1(strName);
break;
case SwapAssignment::Counsellor2:
SetAuxiliaryCounsellor2(strName);
break;
case SwapAssignment::OpenPrayer:
SetOpenPrayer(strName);
break;
case SwapAssignment::Treasures1:
SetTreasures1(strName);
break;
case SwapAssignment::Treasures2:
SetTreasures2(strName);
break;
case SwapAssignment::Living1:
SetLiving1(strName);
break;
case SwapAssignment::Living2:
SetLiving2(strName);
break;
case SwapAssignment::ConductorCBS:
SetCBSConductor(strName);
break;
case SwapAssignment::ReaderCBS:
SetCBSReader(strName);
break;
case SwapAssignment::ClosePrayer:
SetClosePrayer(strName);
break;
}
}
Then I moved the code I mentioned with a little adjustment into a new method:
// AJT v18.1.6
void CChristianLifeMinistryEditorDlg::SwapAssignments(UINT nID, SwapAssignment eAssignment)
{
// We need to locate the name for this assignment
auto iter = m_mapSwapAssignments.find(nID);
if (iter != m_mapSwapAssignments.end())
{
// We found it
CChristianLifeMinistryEntry *pReplacement = m_mapSwapAssignments[nID];
CString strExistingName = _T(""), strReplacementName = _T("");
GetDlgItemText(m_iSwapAssignmentSourceID, strExistingName);
CString strPrompt = _T("");
strPrompt.Format(_T("Swap assignments:\n\n%s - %s\n%s - %s\n\nPlease confirm."),
m_pEntry->GetMeetingDateAsString(),
(LPCTSTR)strExistingName,
pReplacement->GetMeetingDateAsString(),
(LPCTSTR)pReplacement->GetName(eAssignment));
if (AfxMessageBox(strPrompt, MB_ICONQUESTION | MB_YESNO) == IDYES)
{
strReplacementName = pReplacement->GetName(eAssignment);
pReplacement->SetName(strExistingName, eAssignment);
if (pReplacement == m_pEntry) // Swapping assignments on same meeting!
SetDlgItemText(IDC_COMBO_OCLM_CBS_READER, strExistingName);
SetDlgItemText(m_iSwapAssignmentSourceID, strReplacementName);
SetModified(true);
}
}
}
So now my 11 handlers look similar to this:
// AJT v18.1.6
void CChristianLifeMinistryEditorDlg::OnSwapWithCBSReaderAssignment(UINT nID)
{
SwapAssignments(nID, SwapAssignment::ReaderCBS);
}
It works. But I see a new comment has been added to my question with a link so I will see if I can get anywhere.

Answer 1

So lets refactor the code in stages.
Stage 1:
Isolate the common functionality, first, in a generic function OnSwapWith
template<typename Function>
void CChristianLifeMinistryEditorDlg::OnSwapWith(Function && function,
UINT nID)
{
// We need to locate the name for this assignment
auto iter = m_mapSwapAssignments.find(nID);
if (iter != m_mapSwapAssignments.end())
{
// We found it
CChristianLifeMinistryEntry *pReplacement = m_mapSwapAssignments[nID];
CString strExistingName = _T(""), strReplacementName = _T("");
GetDlgItemText(m_iSwapAssignmentSourceID, strExistingName);
CString strPrompt = _T("");
strPrompt.Format(_T("Swap assignments:\n\n%s - %s\n%s - %s\n\nPlease confirm."),
m_pEntry->GetMeetingDateAsString(),
(LPCTSTR)strExistingName,
pReplacement->GetMeetingDateAsString(),
(LPCTSTR)pReplacement->GetChairman());
if (AfxMessageBox(strPrompt, MB_ICONQUESTION | MB_YESNO) == IDYES)
{
function();
SetDlgItemText(m_iSwapAssignmentSourceID, strReplacementName);
SetModified(true);
}
}
}
void CChristianLifeMinistryEditorDlg::OnSwapWithChairmanAssignment(UINT nID)
{
auto ChairmanAssignment = [&]() // capture by reference (i.e. &)
{
strReplacementName = pReplacement->GetChairman();
pReplacement->SetChairman(strExistingName);
};
CChristianLifeMinistryEditorDlg::OnSwapWith(ChairmanAssignment, nID);
}
void CChristianLifeMinistryEditorDlg::OnSwapWithOpenPrayerAssignment(UINT nID)
{
auto OpenPrayerAssignment = [&]() // capture by reference (i.e. &)
{
strReplacementName = pReplacement->GetOpenPrayer();
pReplacement->SetOpenPrayer(strExistingName);
};
CChristianLifeMinistryEditorDlg::OnSwapWith(OpenPrayerAssignment, nID);
}
void CChristianLifeMinistryEditorDlg::OnSwapWithClosePrayerAssignment(UINT nID)
{
auto ClosePrayerAssignment = [&]() // capture by reference (i.e. &)
{
strReplacementName = pReplacement->GetClosePrayer();
pReplacement->SetClosePrayer(strExistingName);
};
CChristianLifeMinistryEditorDlg::OnSwapWith(ClosePrayerAssignment, nID);
}
// and similarly other functions can be defined
After this refactoring, we at least have reduced one level of redundancy.
In this refactoring we have captured everything by reference in the line:
auto ChairmanAssignment = [&]() {};
While capturing by reference, everything is being captured, such as this pointer.
That is why this statement is working :
strReplacementName = pReplacement->GetChairman();
It gets expanded into:
this->strReplacementName = pReplacement->GetChairman();
Stage 2:
Understand that essentially what you are using, were just some generic getters and setters.
So lets refactor it further:
// instead of passing one function, we will pass two : getter and setter
template<typename GetterFunction,
typename SetterFunction>
void CChristianLifeMinistryEditorDlg::OnSwapWith(GetterFunction && getter,
SetterFunction && setter,
UINT nID)
{
...
if (AfxMessageBox(strPrompt, MB_ICONQUESTION | MB_YESNO) == IDYES)
{
strReplacementName = getter(pReplacement);
setter(pReplacement, strExistingName);
SetDlgItemText(m_iSwapAssignmentSourceID, strReplacementName);
SetModified(true);
}
...
}
And the caller side
void CChristianLifeMinistryEditorDlg::OnSwapWithChairmanAssignment(UINT nID)
{
auto getter = [](CChristianLifeMinistryEntry * pReplacement)
{ // remove the captures now, since we are getting the state with the pointer
return pReplacement->GetChairman();
};
auto setter = [](CChristianLifeMinistryEntry * pReplacement,
CString const & strExistingName)
{
pReplacement->SetChairman(strExistingName);
};
CChristianLifeMinistryEditorDlg::OnSwapWith(getter, setter, nID);
}
Final working code
The 11 menu event handlers look something like:
void CChristianLifeMinistryEditorDlg::OnSwapWithChairmanAssignment(UINT nID)
{
auto getter = [](CChristianLifeMinistryEntry * pReplacement)
{
return pReplacement->GetChairman();
};
auto setter = [](CChristianLifeMinistryEntry * pReplacement,
CString & strExistingName)
{
pReplacement->SetChairman(strExistingName);
};
CChristianLifeMinistryEditorDlg::OnSwapWith(getter, setter,
nID, IDC_COMBO_OCLM_CHAIRMAN);
}
The templated function now looks like:
template<typename GetterFunction, typename SetterFunction>
void CChristianLifeMinistryEditorDlg::OnSwapWith(GetterFunction && getter,
SetterFunction && setter,
UINT nID,
UINT nReplacementCtrlID)
{
// We need to locate the name for this assignment
auto iter = m_mapSwapAssignments.find(nID);
if (iter != m_mapSwapAssignments.end())
{
// We found it
CChristianLifeMinistryEntry *pReplacement = m_mapSwapAssignments[nID];
CString strExistingName = _T(""), strReplacementName = _T("");
GetDlgItemText(m_iSwapAssignmentSourceID, strExistingName);
CString strPrompt = _T("");
strPrompt.Format(_T("Swap assignments:\n\n%s - %s\n%s - %s\n\nPlease confirm."),
m_pEntry->GetMeetingDateAsString(),
(LPCTSTR)strExistingName,
pReplacement->GetMeetingDateAsString(),
(LPCTSTR)getter(pReplacement));
if (AfxMessageBox(strPrompt, MB_ICONQUESTION | MB_YESNO) == IDYES)
{
strReplacementName = getter(pReplacement);
setter(pReplacement, strExistingName);
if (pReplacement == m_pEntry) // Swapping assignments on same meeting!
SetDlgItemText(nReplacementCtrlID, strExistingName);
SetDlgItemText(m_iSwapAssignmentSourceID, strReplacementName);
SetModified(true);
}
}
}