feat: if constexpr

chapters/chapter_02/CMakeLists.txt

@@ -1,6 +1,12 @@
 add_library(
-  chapter_02 src/initlist.cpp src/null.cpp src/constexp.cpp src/ifswitch.cpp
-             src/structured_binding.cpp src/type_inference.cpp)
+  chapter_02
+  src/initlist.cpp
+  src/null.cpp
+  src/constexp.cpp
+  src/ifswitch.cpp
+  src/structured_binding.cpp
+  src/type_inference.cpp
+  src/if_constexpr.cpp)
 
 target_compile_features(chapter_02 PUBLIC cxx_std_20)
 

chapters/chapter_02/include/if_constexpr.h

@@ -0,0 +1,9 @@
+#pragma once
+
+#include "chapter_interface.h"
+
+class IfConstexprTest : public ChapterTest {
+public:
+  virtual void run() override;
+  virtual const char *name() const override { return "If constexpr test"; }
+};

chapters/chapter_02/src/if_constexpr.cpp

@@ -0,0 +1,24 @@
+#include <iostream>
+#include <type_traits>
+
+#include "if_constexpr.h"
+
+void print_decltype(auto var) {
+  std::cout << "variable with value " << var << " is of type ";
+
+  if constexpr (std::is_same<decltype(var), int>::value) {
+    std::cout << "int";
+  } else if constexpr (std::is_same<decltype(var), double>::value) {
+    std::cout << "double";
+  } else {
+    std::cout << "unknown";
+  }
+
+  std::cout << std::endl;
+}
+
+void IfConstexprTest::run() {
+  print_decltype(23);
+  print_decltype(23.5);
+  print_decltype("42");
+}

src/main.cpp

@@ -4,6 +4,7 @@
 #include <vector>
 
 #include "constexp.h"
+#include "if_constexpr.h"
 #include "ifswitch.h"
 #include "initlist.h"
 #include "null.h"
@@ -24,6 +25,7 @@ int main(int argc, char **argv) {
   chapter_2_tests.emplace_back(std::make_unique<InitListTest>());
   chapter_2_tests.emplace_back(std::make_unique<StructuredBindingTest>());
   chapter_2_tests.emplace_back(std::make_unique<TypeInferenceTest>());
+  chapter_2_tests.emplace_back(std::make_unique<IfConstexprTest>());
 
   for (auto &test : chapter_2_tests) {
     std::cout << "\n" << test->name() << ":" << std::endl;