From 730633f15a176af90ee4aedc169ba581df0d3b2f Mon Sep 17 00:00:00 2001
From: Michael Mandl <mandlm@molez.net>
Date: Wed, 18 Oct 2023 20:29:41 +0200
Subject: [PATCH] feat: test constexpr

---
 CMakeLists.txt   |  3 ++-
 src/constexp.cpp | 27 +++++++++++++++++++++++++++
 src/constexp.h   |  5 +++++
 src/main.cpp     |  6 ++++++
 4 files changed, 40 insertions(+), 1 deletion(-)
 create mode 100644 src/constexp.cpp
 create mode 100644 src/constexp.h

diff --git a/CMakeLists.txt b/CMakeLists.txt
index c543d70..dfc39b8 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -12,7 +12,8 @@ include(ExportCompileCommands)
 configure_file("${PROJECT_SOURCE_DIR}/include/version.h.in"
                "${PROJECT_BINARY_DIR}/include/version.h")
 
-add_executable(hello src/main.cpp src/null.cpp)
+add_executable(hello src/main.cpp src/null.cpp src/constexp.cpp)
+
 target_compile_features(hello PUBLIC cxx_std_20)
 
 target_include_directories(hello PRIVATE "${PROJECT_BINARY_DIR}/include")
diff --git a/src/constexp.cpp b/src/constexp.cpp
new file mode 100644
index 0000000..f0a5d73
--- /dev/null
+++ b/src/constexp.cpp
@@ -0,0 +1,27 @@
+#include "constexp.h"
+#include <iostream>
+
+constexpr unsigned int fibonacci(const unsigned int n) {
+  if (n == 1 || n == 2) {
+    return 1;
+  }
+
+  return fibonacci(n - 2) + fibonacci(n - 1);
+}
+
+void constexp::test() {
+  std::cout << "Fibonacci(10): ";
+  for (const unsigned int n : {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}) {
+    std::cout << fibonacci(n) << " ";
+  }
+  std::cout << std::endl;
+
+  int arr_1[fibonacci(10)];
+  std::cout << "Array is " << sizeof(arr_1) / sizeof(int) << " items long"
+            << std::endl;
+
+  constexpr unsigned int arr_2_len = 10;
+  int arr_2[arr_2_len];
+  std::cout << "Array is " << sizeof(arr_2) / sizeof(int) << " items long"
+            << std::endl;
+}
diff --git a/src/constexp.h b/src/constexp.h
new file mode 100644
index 0000000..362b4ff
--- /dev/null
+++ b/src/constexp.h
@@ -0,0 +1,5 @@
+#pragma once
+
+namespace constexp {
+void test();
+};
diff --git a/src/main.cpp b/src/main.cpp
index fbea74c..e7a4ebb 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -3,6 +3,7 @@
 
 #include "version.h"
 
+#include "constexp.h"
 #include "null.h"
 
 int main(int argc, char **argv) {
@@ -10,8 +11,13 @@ int main(int argc, char **argv) {
   std::cout << "Running " << PROJECT_NAME << ", version " << VERSION << "\n"
             << std::endl;
 
+  std::cout << "Null test:" << std::endl;
   null::test();
 
+  std::cout << "\n"
+            << "Constexpr test:" << std::endl;
+  constexp::test();
+
   std::cout << "\nExiting" << std::endl;
 
   return EXIT_SUCCESS;