From dccea47e9bc322d654902a1db4fc52cbf6dd0cd7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?John=20Ankarstr=C3=B6m?= <john@ankarstrom.se>
Date: Tue, 26 Jul 2022 18:51:15 +0200
Subject: Improve Win32Error, library handling code.

---
 c/common.cpp | 32 ++------------------------------
 c/common.h   | 44 ++++++++++++++++++++++++++++----------------
 c/main.cpp   | 31 +++++++++++++++----------------
 3 files changed, 45 insertions(+), 62 deletions(-)

diff --git a/c/common.cpp b/c/common.cpp
index 155c099..c4624c0 100644
--- a/c/common.cpp
+++ b/c/common.cpp
@@ -4,8 +4,8 @@
 
 /* Win32Error: Exception for Windows API errors. */
 
-Win32Error::Win32Error() : m_dwErr(GetLastError()) {}
-Win32Error::Win32Error(const DWORD dwErr) : m_dwErr(dwErr) {}
+Win32Error::Win32Error() : dwErr(GetLastError()) {}
+Win32Error::Win32Error(const DWORD dwErr) : dwErr(dwErr) {}
 
 Win32Error::~Win32Error()
 {
@@ -15,34 +15,6 @@ Win32Error::~Win32Error()
 		HeapFree(GetProcessHeap(), 0, m_wszMsg);
 }
 
-template <>
-const char* Win32Error::what() const noexcept
-{
-	if (!m_szMsg)
-		FormatMessageA(
-		    FORMAT_MESSAGE_ALLOCATE_BUFFER|FORMAT_MESSAGE_FROM_SYSTEM|FORMAT_MESSAGE_IGNORE_INSERTS,
-		    NULL,
-		    m_dwErr,
-		    MAKELANGID(LANG_ENGLISH, SUBLANG_ENGLISH_US),
-		    (char*)&m_szMsg,
-		    0, NULL);
-	return m_szMsg;
-}
-
-template <>
-const wchar_t* Win32Error::what() const noexcept
-{
-	if (!m_wszMsg)
-		FormatMessageW(
-		    FORMAT_MESSAGE_ALLOCATE_BUFFER|FORMAT_MESSAGE_FROM_SYSTEM|FORMAT_MESSAGE_IGNORE_INSERTS,
-		    NULL,
-		    m_dwErr,
-		    MAKELANGID(LANG_ENGLISH, SUBLANG_ENGLISH_US),
-		    (wchar_t*)&m_wszMsg,
-		    0, NULL);
-	return m_wszMsg;
-}
-
 /* Library: Wrapper for loading and freeing dynamically linked libraries. */
 
 Library::Library(const TCHAR* const tszLibrary)
diff --git a/c/common.h b/c/common.h
index 709a258..3f27ba4 100644
--- a/c/common.h
+++ b/c/common.h
@@ -14,19 +14,45 @@
 template <typename T> std::basic_string<T> BstrFromSz(const char* sz, int iCp = CP_UTF8);
 int EBMessageBox(const TCHAR* tszText, const TCHAR* tszCaption, unsigned uType);
 
+/* Conditionally choose between two values. */
+template <bool B, typename X, typename Y>
+constexpr std::enable_if_t<B == true, X> choose(X x, Y) { return x; }
+template <bool B, typename X, typename Y>
+constexpr std::enable_if_t<B == false, Y> choose(X, Y y) { return y; }
+
+/* Conditionally choose between ANSI and wide string literal. */
+#define AWTEXT(t, s) choose<std::is_same_v<t, wchar_t>>(L"" s, s)
+
+/* Conditionally choose between ANSI and wide Windows API function. */
+#define AWFUN(t, f) choose<std::is_same_v<t, wchar_t>>(f##W, f##A)
+
 struct Win32Error : public std::exception
 {
 	Win32Error();
 	Win32Error(DWORD dwErr);
 	~Win32Error();
 	template <typename T = char> const T* what() const noexcept;
-
+	DWORD dwErr;
 private:
-	DWORD m_dwErr;
 	char* m_szMsg = NULL;
 	wchar_t* m_wszMsg = NULL;
 };
 
+template <typename T>
+const T* Win32Error::what() const noexcept
+{
+	TCHAR* tszMsg = choose<std::is_same_v<T, wchar_t>>(m_wszMsg, m_szMsg);
+	if (!tszMsg)
+		AWFUN(T, FormatMessage)(
+		    FORMAT_MESSAGE_ALLOCATE_BUFFER|FORMAT_MESSAGE_FROM_SYSTEM|FORMAT_MESSAGE_IGNORE_INSERTS,
+		    NULL,
+		    dwErr,
+		    MAKELANGID(LANG_ENGLISH, SUBLANG_ENGLISH_US),
+		    (TCHAR*)&tszMsg,
+		    0, NULL);
+	return tszMsg;
+}
+
 struct Library
 {
 	Library(const TCHAR* tszLibrary);
@@ -79,20 +105,6 @@ inline T prefer(const T x)
 	return x;
 }
 
-/* Conditionally choose between two values. This template is necessary
- * because the ternary conditional operator can choose only between
- * values of the same type. */
-template <bool B, typename X, typename Y>
-constexpr std::enable_if_t<B == true, X> choose(X x, Y) { return x; }
-template <bool B, typename X, typename Y>
-constexpr std::enable_if_t<B == false, Y> choose(X, Y y) { return y; }
-
-/* Conditionally choose between ANSI and wide string literal. */
-#define AWTEXT(t, s) choose<std::is_same_v<t, wchar_t>>(L"" s, s)
-
-/* Conditionally choose between ANSI and wide Windows API function. */
-#define AWFUN(t, f) choose<std::is_same_v<t, wchar_t>>(f##W, f##A)
-
 /* Return integer scaled for current DPI. */
 inline int Dpi(const int i)
 {
diff --git a/c/main.cpp b/c/main.cpp
index 057bf32..2037578 100644
--- a/c/main.cpp
+++ b/c/main.cpp
@@ -167,22 +167,21 @@ static LRESULT CALLBACK CBTProc(const int nCode, const WPARAM wParam, const LPAR
 	g_hWnd = (HWND)wParam;
 
 	/* Look up constants. */
-	if (auto opLib = maybe_make<Library>(TEXT("User32.dll")))
-		if (auto GetDpiForWindow = opLib->GetProcAddress<UINT(HWND)>("GetDpiForWindow"))
-			g_iDPI = GetDpiForWindow(g_hWnd);
-
-	if (auto opLib = maybe_make<Library>(TEXT("uxtheme.dll")))
-		if (opLib->GetProcAddress<void>("SetWindowTheme"))
-			g_bThemes = 1;
-
-	if (auto opLib = maybe_make<Library>(TEXT("User32.dll"))) {
-		if (opLib->GetProcAddress<void>("SystemParametersInfo" WA)) {
-			NONCLIENTMETRICS m;
-			m.cbSize = sizeof(NONCLIENTMETRICS);
-			require(SystemParametersInfo(SPI_GETNONCLIENTMETRICS,
-			    sizeof(NONCLIENTMETRICS), &m, 0));
-			g_hfNormal = require(CreateFontIndirect(&m.lfMessageFont));
-		}
+	if (auto opLib = maybe_make<Library>(TEXT("User32.dll"));
+	    auto GetDpiForWindow = opLib->GetProcAddress<UINT(HWND)>("GetDpiForWindow"))
+		g_iDPI = GetDpiForWindow(g_hWnd);
+
+	if (auto opLib = maybe_make<Library>(TEXT("uxtheme.dll"));
+	    opLib->GetProcAddress<void>("SetWindowTheme"))
+		g_bThemes = 1;
+
+	if (auto opLib = maybe_make<Library>(TEXT("User32.dll"));
+	    opLib->GetProcAddress<void>("SystemParametersInfo" WA)) {
+		NONCLIENTMETRICS m;
+		m.cbSize = sizeof(NONCLIENTMETRICS);
+		require(SystemParametersInfo(SPI_GETNONCLIENTMETRICS,
+		    sizeof(NONCLIENTMETRICS), &m, 0));
+		g_hfNormal = require(CreateFontIndirect(&m.lfMessageFont));
 	} else
 		g_hfNormal = static_cast<HFONT>(require(GetStockObject(DEFAULT_GUI_FONT)));
 
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