From 53abfac6acd04dff80ec6c8cfb0dd53f2f74dadb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?John=20Ankarstr=C3=B6m?= <john@ankarstrom.se>
Date: Mon, 18 Jul 2022 03:25:00 +0200
Subject: Improve Library::GetProcAddress.

It isn't really more safe, but it removes the need for a confusing
function pointer cast, which is easy to get wrong. As far as the
compiler is concerned, the result is literally the same, but it does
force the caller to (indirectly, via the template parameter) cast the
return value, which may be a good thing.
---
 c/common.cpp |  5 -----
 c/common.h   | 30 ++++++++++++++++++------------
 c/main.cpp   |  6 +++---
 3 files changed, 21 insertions(+), 20 deletions(-)

diff --git a/c/common.cpp b/c/common.cpp
index c04d986..d503133 100644
--- a/c/common.cpp
+++ b/c/common.cpp
@@ -57,8 +57,3 @@ Library::~Library()
 {
 	FreeLibrary(m_hModule);
 }
-
-void* Library::GetProcAddress(const char* const szProc)
-{
-	return (void*)::GetProcAddress(m_hModule, szProc);
-}
diff --git a/c/common.h b/c/common.h
index 169b748..a4f1fd4 100644
--- a/c/common.h
+++ b/c/common.h
@@ -27,23 +27,15 @@ struct Library
 {
 	Library(const TCHAR* tszLibrary);
 	~Library();
-	void* GetProcAddress(const char* szProc);
+	template <typename T> T* GetProcAddress(const char* szProc);
 private:
 	HMODULE m_hModule;
 };
 
-inline int Cmp(const int a, const int b)
+template <typename T>
+T* Library::GetProcAddress(const char* const szProc)
 {
-	if (a == b) return 0;
-	if (a > b) return 1;
-	return -1;
-}
-
-/* Return integer scaled for current DPI. */
-inline int Dpi(const int i)
-{
-	extern int g_iDPI;
-	return MulDiv(i, g_iDPI, 96);
+	return (T*)(void*)::GetProcAddress(m_hModule, szProc);
 }
 
 /* Create and return an object of type C. If construction fails,
@@ -59,4 +51,18 @@ std::optional<C> try_make(T ...args)
 	}
 }
 
+/* Return integer scaled for current DPI. */
+inline int Dpi(const int i)
+{
+	extern int g_iDPI;
+	return MulDiv(i, g_iDPI, 96);
+}
+
+inline int Cmp(const int a, const int b)
+{
+	if (a == b) return 0;
+	if (a > b) return 1;
+	return -1;
+}
+
 #endif
diff --git a/c/main.cpp b/c/main.cpp
index 2e2fbbf..08e6b96 100644
--- a/c/main.cpp
+++ b/c/main.cpp
@@ -156,16 +156,16 @@ static LRESULT CALLBACK CBTProc(const int nCode, const WPARAM wParam, const LPAR
 
 	/* Look up constants. */
 	if (auto opLib = try_make<Library>(TEXT("User32.dll")))
-		if (auto GetDpiForWindow = (UINT (*)(HWND))opLib->GetProcAddress("GetDpiForWindow"))
+		if (auto GetDpiForWindow = opLib->GetProcAddress<UINT(HWND)>("GetDpiForWindow"))
 			g_iDPI = GetDpiForWindow(g_hWnd);
 
 	if (auto opLib = try_make<Library>(TEXT("uxtheme.dll")))
-		if (opLib->GetProcAddress("SetWindowTheme"))
+		if (opLib->GetProcAddress<void>("SetWindowTheme"))
 			g_bThemes = 1;
 
 	LOGFONT lf;
 	if (auto opLib = try_make<Library>(TEXT("User32.dll"))) {
-		if (opLib->GetProcAddress("SystemParametersInfo" WA)) {
+		if (opLib->GetProcAddress<void>("SystemParametersInfo" WA)) {
 			NONCLIENTMETRICS m;
 			m.cbSize = sizeof(NONCLIENTMETRICS);
 			SystemParametersInfo(SPI_GETNONCLIENTMETRICS, sizeof(NONCLIENTMETRICS), &m, 0);
-- 
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