Add (optional) main function to library

include/Gedeng.h

@@ -3,4 +3,6 @@
 #include "Gedeng/Application.h"
 #include "Gedeng/Logger.h"
 #include "Gedeng/String.h"
-#include "Gedeng/Vector.h"
+#include "Gedeng/Vector.h"
+
+#include "Gedeng/EntryPoint.h"

include/Gedeng/Application.h

@@ -12,4 +12,7 @@ class Application {
     void run();
 };
 
+// To be defined in client applications
+Application *create_application();
+
 } // namespace Gedeng

include/Gedeng/EntryPoint.h

@@ -0,0 +1,18 @@
+#pragma once
+
+#include "Gedeng/Application.h"
+
+extern Gedeng::Application *Gedeng::create_application();
+
+// If the user program defines GEDENG_MAIN, supply this main function
+#ifdef GEDENG_MAIN
+int main() {
+    Gedeng::Application *app = Gedeng::create_application();
+
+    app->run();
+
+    delete app;
+
+    return 0;
+}
+#endif

test/test-app/main.cpp

@@ -1,3 +1,4 @@
+#define GEDENG_MAIN
 #include <Gedeng.h>
 
 class TestApp : public Gedeng::Application {
@@ -7,10 +8,6 @@ class TestApp : public Gedeng::Application {
     ~TestApp() = default;
 };
 
-int main() {
+Gedeng::Application *Gedeng::create_application() {
-    TestApp *app = new TestApp();
+    return new TestApp();
-
+}
-    app->run();
-
-    delete app;
-}