@@ -58,6 +58,7 @@
                 1. [Virtual inheritance](http://stackoverflow.com/questions/21558/in-c-what-is-a-virtual-base-class)
     1.  [namespace](namespace.cpp)
     1.  [template](template.cpp)
+        1.  [constexpr if](constexpr_if.cpp)
     1.  [exception](exception.cpp)
     1.  [typedef](typedef.cpp)
     1.  [typecast](typecast.cpp)
 
@@ -0,0 +1,24 @@
+// https://stackoverflow.com/questions/12160765/if-else-at-compile-time-in-c/54647315#54647315
+// https://stackoverflow.com/questions/37617677/implementing-a-compile-time-static-if-logic-for-different-string-types-in-a-co
+
+#if __cplusplus >= 201703L
+#include <cassert>
+#include <type_traits>
+
+template <class T>
+struct MyClass {
+    int myFunc() {
+        if constexpr(std::is_integral<T>())
+            return 1;
+        else
+            return 2;
+    }
+};
+#endif
+
+int main() {
+#if __cplusplus >= 201703L
+    assert(MyClass<int>().myFunc() == 1);
+    assert(MyClass<float>().myFunc() == 2);
+#endif
+}
@@ -1,45 +1,43 @@
-/*
-# preprocessor
-
-    Almost the same as the C one:
-    http://stackoverflow.com/questions/5085533/is-a-c-preprocessor-identical-to-a-c-preprocessor
-
-    The major differences are the predefined macros.
-*/
+// # preprocessor
+//
+// Almost the same as the C one:
+// http://stackoverflow.com/questions/5085533/is-a-c-preprocessor-identical-to-a-c-preprocessor
+//
+// The major differences are the predefined macros.
 
 #include "common.hpp"
 
 int main() {
-    /*
-    # Standard preprocessor macros
-    */
+    // # __cplusplus
+    //
+    // Defined only if using C++ compiler.
+    //
+    // Its value is the actual C++ version in use
+    // in a similar way to __STDC_VERSION__
+    //
+    // C99 says that the C compiler must not define it.
+    //
+    // GCC 6.4 has the -std=c++17 option early, even before
+    // __cplusplus == 201703L was reached.
     {
-        /*
-        # __cplusplus
-
-            Defined only if using C++ compiler.
-
-            Its value is the actual C++ version in use in a similar way to __STDC_VERSION__
-
-            Values:
-
-            - C++98: 199711L
-            - C++11: 201103L
-
-            C99 says that the C compiler must not define it.
-        */
-        {
-            std::cout << "__cplusplus = " << __cplusplus << std::endl;
-
-#if __cplusplus >= 201103L
-            std::cout << "C++11 code" << std::endl;
+        std::cout << "__cplusplus = " << __cplusplus << std::endl;
+#if __cplusplus == 199711L
+        std::cout << "C++98" << std::endl;
+#endif
+#if __cplusplus == 201103L
+        std::cout << "C++11" << std::endl;
+#endif
+#if __cplusplus == 201402L
+        std::cout << "C++14" << std::endl;
 #endif
-        }
+#if __cplusplus == 201703L
+        std::cout << "C++17" << std::endl;
+#endif
+    }
 
 #ifdef __STDCPP_THREADS__
-        // TODO why not defined even though I do have multithreading?
-        std::cout << "__STDCPP_THREADS__" << __cplusplus << std::endl;
-        assert(__STDCPP_THREADS__ == 1);
+    // TODO why not defined even though I do have multithreading?
+    std::cout << "__STDCPP_THREADS__" << __cplusplus << std::endl;
+    assert(__STDCPP_THREADS__ == 1);
 #endif
-    }
 }
@@ -1,12 +1,10 @@
-/*
-# regex
-
-    Finally they are supported!
-
-    Many types are supported: Javascript, grep, awk, ...
-
-    It is probably saner and more powerful to stick to Javascript regexes.
-*/
+// # regex
+//
+// Finally they are supported!
+//
+// Many flavours supported: JavaScript, grep, awk, ...
+//
+// It is probably saner and more powerful to stick to JavaScript regexes.
 
 #include "common.hpp"