Fix bug in and rename throw_nil, warn_nil.

In warn_nil, the return value was undefined on exception -- I think.

While informative, the names throw_nil and warn_nil don't work very
well in conditionals:

  if (warn_nil<f>(...)) g();

sounds like g should be called if f returns nil and a warning is
issued. But it is actually the other way around; g is called if f is
successful.

  if (prefer<f>(...)) g();

sounds less like that.

5 files changed, 29 insertions, 30 deletions

diff --git a/c/common.cpp b/c/common.cpp
index b85be49..7981801 100644
--- a/c/common.cpp
+++ b/c/common.cpp
@@ -87,8 +87,8 @@ static LRESULT CALLBACK CBTProc(const int nCode, const WPARAM wParam, const LPAR
 int EBMessageBox(const TCHAR* const tszText, const TCHAR* const tszCaption, const unsigned uType)
 {
 	extern HWND g_hWnd;
-	HHOOK hHook = throw_nil<SetWindowsHookEx>(WH_CBT, CBTProc, (HINSTANCE)NULL, GetCurrentThreadId());
+	HHOOK hHook = require<SetWindowsHookEx>(WH_CBT, CBTProc, (HINSTANCE)NULL, GetCurrentThreadId());
 	int r = MessageBox(g_hWnd, tszText, tszCaption, uType);
-	throw_nil<UnhookWindowsHookEx>(hHook);
+	require<UnhookWindowsHookEx>(hHook);
 	return r;
 }
diff --git a/c/common.h b/c/common.h
index a4f73e5..6b29ed5 100644
--- a/c/common.h
+++ b/c/common.h
@@ -55,7 +55,7 @@ std::optional<T> maybe_make(U... xs)
 
 /* Call Windows API function, throwing error on NULL. */
 template <auto F, typename... T>
-inline auto throw_nil(T... xs)
+inline auto require(T... xs)
 {
 	auto r = F(xs...);
 	if (!r) throw Win32Error(GetLastError());
@@ -64,15 +64,14 @@ inline auto throw_nil(T... xs)
 
 /* Call Windows API function, showing a warning on NULL. */
 template <auto F, typename... T>
-inline auto warn_nil(T... xs)
+inline auto prefer(T... xs)
 {
-	decltype(F(std::declval<T>()...)) r;
 	try {
-		r = throw_nil<F>(xs...);
+		return require<F>(xs...);
 	} catch (Win32Error& e) {
 		EBMessageBox(e.twhat(), TEXT("System Error"), MB_ICONWARNING);
+		return (decltype(F(std::declval<T>()...)))NULL;
 	}
-	return r;
 }
 
 /* Return integer scaled for current DPI. */
diff --git a/c/episodelistview.cpp b/c/episodelistview.cpp
index e70cc06..6ed9146 100644
--- a/c/episodelistview.cpp
+++ b/c/episodelistview.cpp
@@ -90,7 +90,7 @@ LRESULT EpisodeListView::HandleNotify(const LPARAM lParam)
 		    {
 			extern HFONT g_hfBold;
 			if (!Pl("track_episodes","watched",pLvCd->nmcd.lItemlParam)) {
-				throw_nil<SelectObject>(pLvCd->nmcd.hdc, g_hfBold);
+				require<SelectObject>(pLvCd->nmcd.hdc, g_hfBold);
 				return CDRF_NEWFONT;
 			}
 			break;
@@ -125,7 +125,7 @@ LRESULT EpisodeListView::HandleNotify(const LPARAM lParam)
 	    {
 		extern HMENU g_hPopupMenu;
 		const DWORD dwPos = GetMessagePos();
-		throw_nil<TrackPopupMenu>(g_hPopupMenu, TPM_RIGHTBUTTON,
+		require<TrackPopupMenu>(g_hPopupMenu, TPM_RIGHTBUTTON,
 		    LOWORD(dwPos), HIWORD(dwPos), 0,
 		    m_hWndParent, (const RECT*)NULL);
 		break;
diff --git a/c/listview.cpp b/c/listview.cpp
index fa99793..056a17b 100644
--- a/c/listview.cpp
+++ b/c/listview.cpp
@@ -13,7 +13,7 @@ ListView::ListView(const HWND hWndParent, const HMENU hMenu, const DWORD dwStyle
 {
 	m_hWndParent = hWndParent;
 	m_bHeader = !(dwStyle & LVS_NOCOLUMNHEADER);
-	hWnd = throw_nil<CreateWindowEx>(
+	hWnd = require<CreateWindowEx>(
 	    WS_EX_CLIENTEDGE,
 	    WC_LISTVIEW,
 	    TEXT(""),
@@ -21,7 +21,7 @@ ListView::ListView(const HWND hWndParent, const HMENU hMenu, const DWORD dwStyle
 	    0, 0, 0, 0,
 	    m_hWndParent, hMenu, GetModuleHandle(NULL), this);
 
-	if (throw_nil<SetProp>(hWnd, TEXT("this"), (HANDLE)this))
+	if (require<SetProp>(hWnd, TEXT("this"), (HANDLE)this))
 		m_prevProc = (WNDPROC)SetWindowLongPtr(hWnd,
 		    GWLP_WNDPROC, (LONG_PTR)::WndProc);
 
diff --git a/c/main.cpp b/c/main.cpp
index f9bdced..1a50c6f 100644
--- a/c/main.cpp
+++ b/c/main.cpp
@@ -89,10 +89,10 @@ int WINAPI WinMain(const HINSTANCE hInstance, const HINSTANCE, char* const, cons
 	INITCOMMONCONTROLSEX icc;
 	icc.dwSize = sizeof(icc);
 	icc.dwICC = ICC_WIN95_CLASSES;
-	throw_nil<InitCommonControlsEx>(&icc);
+	require<InitCommonControlsEx>(&icc);
 
-	g_hPopupMenu = throw_nil<LoadMenu>((HINSTANCE)NULL, MAKEINTRESOURCE(IDR_POPUPMENU));
-	g_hPopupMenu = throw_nil<GetSubMenu>(g_hPopupMenu, 0);
+	g_hPopupMenu = require<LoadMenu>((HINSTANCE)NULL, MAKEINTRESOURCE(IDR_POPUPMENU));
+	g_hPopupMenu = require<GetSubMenu>(g_hPopupMenu, 0);
 
 	WNDCLASSEX wc;
 	memset(&wc, 0, sizeof(WNDCLASSEX));
@@ -105,23 +105,23 @@ int WINAPI WinMain(const HINSTANCE hInstance, const HINSTANCE, char* const, cons
 	wc.lpszMenuName	 = MAKEINTRESOURCE(IDR_MENU);
 	wc.lpszClassName = TEXT("Episode Browser");
 	wc.hIconSm	 = LoadIcon(NULL, IDI_APPLICATION);
-	throw_nil<RegisterClassEx>(&wc);
+	require<RegisterClassEx>(&wc);
 
 	/* Create window. A CBT hook is used to initialize important
 	 * global variables before any messages are sent to the new
 	 * window. It is vital that the hook is set up correctly. */
-	const HHOOK hHook = throw_nil<SetWindowsHookEx>(WH_CBT, CBTProc,
+	const HHOOK hHook = require<SetWindowsHookEx>(WH_CBT, CBTProc,
 	    (HINSTANCE)NULL, GetCurrentThreadId());
-	const HWND hWnd = throw_nil<CreateWindowEx>(
+	const HWND hWnd = require<CreateWindowEx>(
 	    0,
 	    TEXT("Episode Browser"),
 	    TEXT("Episode Browser"),
 	    WS_OVERLAPPEDWINDOW,
 	    CW_USEDEFAULT, CW_USEDEFAULT, 0, 0,
 	    (HWND)NULL, (HMENU)NULL, hInstance, (void*)NULL);
-	throw_nil<UnhookWindowsHookEx>(hHook);
+	require<UnhookWindowsHookEx>(hHook);
 
-	g_hWndStatus = throw_nil<CreateWindowEx>(
+	g_hWndStatus = require<CreateWindowEx>(
 	    0,
 	    STATUSCLASSNAME,
 	    (const TCHAR*)NULL,
@@ -171,17 +171,17 @@ static LRESULT CALLBACK CBTProc(const int nCode, const WPARAM wParam, const LPAR
 		if (opLib->GetProcAddress<void>("SystemParametersInfo" WA)) {
 			NONCLIENTMETRICS m;
 			m.cbSize = sizeof(NONCLIENTMETRICS);
-			throw_nil<SystemParametersInfo>(SPI_GETNONCLIENTMETRICS,
+			require<SystemParametersInfo>(SPI_GETNONCLIENTMETRICS,
 			    sizeof(NONCLIENTMETRICS), &m, 0);
-			g_hfNormal = throw_nil<CreateFontIndirect>(&m.lfMessageFont);
+			g_hfNormal = require<CreateFontIndirect>(&m.lfMessageFont);
 		}
 	} else
-		g_hfNormal = static_cast<HFONT>(throw_nil<GetStockObject>(DEFAULT_GUI_FONT));
+		g_hfNormal = static_cast<HFONT>(require<GetStockObject>(DEFAULT_GUI_FONT));
 
 	LOGFONT lf;
-	throw_nil<GetObject>(g_hfNormal, sizeof(LOGFONT), &lf);
+	require<GetObject>(g_hfNormal, sizeof(LOGFONT), &lf);
 	lf.lfWeight = FW_BOLD;
-	g_hfBold = throw_nil<CreateFontIndirect>(&lf);
+	g_hfBold = require<CreateFontIndirect>(&lf);
 
 	/* Create child windows. */
 	g_pDlv = new DataListView(g_hWnd);
@@ -237,7 +237,7 @@ LRESULT CALLBACK WndProc(const HWND hWnd, const UINT uMsg, const WPARAM wParam,
 	    {
 		const RECT* const lpr = (RECT*)lParam;
 		g_iDPI = HIWORD(wParam);
-		warn_nil<SetWindowPos>(hWnd, (HWND)NULL,
+		prefer<SetWindowPos>(hWnd, (HWND)NULL,
 		    lpr->left, lpr->top,
 		    lpr->right-lpr->left,
 		    lpr->bottom-lpr->top,
@@ -280,7 +280,7 @@ LRESULT CALLBACK WndProc(const HWND hWnd, const UINT uMsg, const WPARAM wParam,
 					TEXT("")));
 			} else {
 				i = 0;
-				warn_nil<KillTimer>(hWnd, IDT_TIMER);
+				prefer<KillTimer>(hWnd, IDT_TIMER);
 				g_pElv->Update();
 			}
 			break;
@@ -302,8 +302,8 @@ LRESULT CALLBACK WndProc(const HWND hWnd, const UINT uMsg, const WPARAM wParam,
 		case IDM_FILE_FETCH_SCREENWRITERS:
 			if (g_bThread) break;
 			Pl("episode_data","thread_create","update_screenwriters",&g_aThread);
-		t:	warn_nil<KillTimer>(hWnd, IDT_TIMER);
-			if (!SetTimer(hWnd, IDT_TIMER, 500, (TIMERPROC)NULL)) break;
+		t:	KillTimer(hWnd, IDT_TIMER);
+			if (!prefer<SetTimer>(hWnd, IDT_TIMER, 500, (TIMERPROC)NULL)) break;
 			SendMessage(g_hWndStatus, SB_SETTEXT, MAKEWPARAM(1,0), (LPARAM)TEXT("."));
 			g_bThread = 1;
 			break;
@@ -514,14 +514,14 @@ void UpdateLayout()
 
 	/* Resize data list view. */
 	cyDlv = rc.bottom-yStatus-g_pDlv->Height();
-	throw_nil<MoveWindow>(g_pDlv->hWnd, 0, cyDlv, rc.right, rc.bottom-yStatus-cyDlv, TRUE);
+	require<MoveWindow>(g_pDlv->hWnd, 0, cyDlv, rc.right, rc.bottom-yStatus-cyDlv, TRUE);
 	ListView_SetColumnWidth(g_pDlv->hWnd, DLVSIKEY, LVSCW_AUTOSIZE);
 	cxColumn = ListView_GetColumnWidth(g_pDlv->hWnd, 0)+4;
 	ListView_SetColumnWidth(g_pDlv->hWnd, DLVSIKEY, cxColumn);
 	ListView_SetColumnWidth(g_pDlv->hWnd, DLVSIVALUE, rc.right-cxColumn-cxVScroll-4);
 
 	/* Resize episode list view. */
-	throw_nil<MoveWindow>(g_pElv->hWnd, 0, 0, rc.right, cyDlv+1, TRUE);
+	require<MoveWindow>(g_pElv->hWnd, 0, 0, rc.right, cyDlv+1, TRUE);
 	ListView_SetColumnWidth(g_pElv->hWnd, ELVSIEPISODE, LVSCW_AUTOSIZE);
 	cxColumn = ListView_GetColumnWidth(g_pElv->hWnd, ELVSIEPISODE)+4;
 	ListView_SetColumnWidth(g_pElv->hWnd, ELVSIEPISODE, cxColumn);