sfinae hello world

userland/cpp/if_constexpr.cpp

@@ -1,5 +1,4 @@
-// https://cirosantilli.com/linux-kernel-module-cheat#cpp
-
+// https://cirosantilli.com/linux-kernel-module-cheat#cpp-compile-time-magic
 
 #if __cplusplus >= 201703L
 #include <cassert>

userland/cpp/sfinae.cpp

@@ -0,0 +1,40 @@
+// https://cirosantilli.com/linux-kernel-module-cheat#cpp-templates
+
+#include <cassert>
+
+struct HasMyfunc {
+    int myfunc() const { return 1; }
+};
+struct NoHasMyfunc {
+    int myfunc2() const { return 11; }
+};
+
+// int() is the actual return type.
+// t.myfunc() checks that t has method myfunc().
+// The decltype does not have multiple arguments, just a single comma separated expression:
+// https://stackoverflow.com/questions/16044514/what-is-decltype-with-two-arguments
+// Syntax breakdown:
+// https://medium.com/@mortificador/choose-between-different-implementations-depending-on-type-properties-at-compile-time-in-c-68e3fd5cd2f8
+template<class T>
+auto template_func(const T& t) ->
+    decltype(t.myfunc(), int())
+{
+    return t.myfunc();
+}
+
+template<class T>
+auto template_func(const T& t) ->
+    decltype(t.myfunc2(), int())
+{
+    return t.myfunc2();
+}
+
+int main() {
+    // Hello world example.
+    // The correct template is used for the type that has each different method.
+    // If we didn't specify constraints for each template type, C++ would blow up
+    // with multiple possible functions:
+    // https://stackoverflow.com/questions/53441832/sfinae-for-function-body
+    assert(template_func(HasMyfunc()) == 1);
+    assert(template_func(NoHasMyfunc()) == 11);
+}

userland/cpp/template.cpp

@@ -1,4 +1,4 @@
-// https://cirosantilli.com/linux-kernel-module-cheat#cpp
+// https://cirosantilli.com/linux-kernel-module-cheat#cpp-templates
 
 #include <cassert>
 

userland/cpp/template_class_with_static_member.cpp

@@ -1,4 +1,4 @@
-// https://cirosantilli.com/linux-kernel-module-cheat#cpp
+// https://cirosantilli.com/linux-kernel-module-cheat#cpp-templates
 
 #include <cassert>