samples/windll: remove _WIN32 guards, Windows-only sample

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: jll63

samples/windll/CMakeLists.txt

@@ -3,33 +3,25 @@
 # See accompanying file LICENSE_1_0.txt
 # or copy at http://www.boost.org/LICENSE_1_0.txt)
 
-# Illustrates the exe-exports-data / DLL-imports-data pattern on Windows:
-# the exe defines and exports a variable; the DLL imports and reads it.
-#
-# On non-Windows both compilation units are linked into a single executable.
+# Illustrates the dllvar technique: the exe owns (exports) a variable; the
+# DLL imports it. Both see static_answer<answer_dllvar, void>::value as the
+# same linker symbol because the varying base class does not enter the mangled
+# name; SFINAE selects dllexport in the owner and dllimport in the client.
 
-if (WIN32 OR CYGWIN)
-    # Exe exports the registry state and loads the plugin at runtime.
-    add_executable(windll_main main.cpp)
-    target_compile_definitions(windll_main PRIVATE WINDLL_OWNER)
-    set_target_properties(windll_main PROPERTIES ENABLE_EXPORTS ON)
+if (NOT (WIN32 OR CYGWIN))
+    return()
+endif()
 
-    # DLL imports the variable from the exe.
-    add_library(windll_plugin SHARED plugin.cpp)
-    target_link_libraries(windll_plugin PRIVATE windll_main)
-    set_target_properties(windll_plugin PROPERTIES ENABLE_EXPORTS ON)
+add_executable(windll_main main.cpp)
+target_compile_definitions(windll_main PRIVATE WINDLL_OWNER)
+set_target_properties(windll_main PROPERTIES ENABLE_EXPORTS ON)
 
-    # windll_main loads windll_plugin at runtime; build both before testing.
-    add_custom_target(windll_all ALL DEPENDS windll_main windll_plugin)
+add_library(windll_plugin SHARED plugin.cpp)
+target_link_libraries(windll_plugin PRIVATE windll_main)
 
-    add_test(
-        NAME windll
-        COMMAND windll_main
-        WORKING_DIRECTORY $<TARGET_FILE_DIR:windll_main>)
-else()
-    # Non-Windows: single executable, no DLL decoration needed.
-    add_executable(windll_main main.cpp plugin.cpp)
-    target_compile_definitions(windll_main PRIVATE WINDLL_OWNER)
+add_custom_target(windll_all ALL DEPENDS windll_main windll_plugin)
 
-    add_test(NAME windll COMMAND windll_main)
-endif()
+add_test(
+    NAME windll
+    COMMAND windll_main
+    WORKING_DIRECTORY $<TARGET_FILE_DIR:windll_main>)

samples/windll/main.cpp

@@ -7,21 +7,14 @@
 #define WINDLL_OWNER
 #include "shared.hpp"
 #include <cassert>
-#ifdef _WIN32
 #include <windows.h>
-#endif
 
 int main() {
     answer() = 42;
-#ifdef _WIN32
     auto plugin = LoadLibraryA("windll_plugin.dll");
     assert(plugin);
     auto get_answer = reinterpret_cast<int(*)()>(
         GetProcAddress(plugin, "get_answer"));
     assert(get_answer() == 42);
     FreeLibrary(plugin);
-#else
-    extern int get_answer();
-    assert(get_answer() == 42);
-#endif
 }

samples/windll/plugin.cpp

@@ -6,12 +6,6 @@
 // Client: answer_dllvar derives from dllimport_tag here (no WINDLL_OWNER).
 #include "shared.hpp"
 
-#ifdef _WIN32
-#define EXPORT __declspec(dllexport)
-#else
-#define EXPORT
-#endif
-
-// answer() returns a reference to the same static_answer<answer_dllvar, void>::value
-// that main.cpp owns — one shared linker symbol, bound via dllimport.
-extern "C" EXPORT int get_answer() { return answer(); }
+// answer() returns a reference to static_answer<answer_dllvar, void>::value —
+// the one shared linker symbol — bound via dllimport.
+extern "C" __declspec(dllexport) int get_answer() { return answer(); }

samples/windll/shared.hpp

@@ -15,25 +15,20 @@ struct dllimport_tag {};
 // A base class does not appear in a class's mangled name, so
 // static_answer<answer_dllvar>::value resolves to the SAME linker symbol in
 // all modules — only the export/import attribute differs.
-#ifdef _WIN32
-# ifdef WINDLL_OWNER
+#ifdef WINDLL_OWNER
 struct answer_dllvar : dllexport_tag {};
-# else
-struct answer_dllvar : dllimport_tag {};
-# endif
 #else
-struct answer_dllvar {};  // no decoration needed on ELF platforms
+struct answer_dllvar : dllimport_tag {};
 #endif
 
-// Primary template: plain static variable (non-Windows and catch-all).
+// Primary template: plain static variable (catch-all).
 template<class Tag, typename = void>
 struct static_answer {
     static int value;
 };
 template<class Tag, typename Enable>
 int static_answer<Tag, Enable>::value;
 
-#ifdef _WIN32
 // Specialization for dllexport: selected when Tag derives from dllexport_tag.
 // enable_if_t<true> evaluates to void, so the instantiation is
 // static_answer<answer_dllvar, void> — same mangled name as the dllimport case.
@@ -52,7 +47,6 @@ struct static_answer<Tag,
     std::enable_if_t<std::is_base_of_v<dllimport_tag, Tag>>> {
     static __declspec(dllimport) int value;
 };
-#endif
 
 // Accessor: always refers to static_answer<answer_dllvar, void>::value —
 // the one shared linker symbol — regardless of which specialization is active.