From ed8b28c76514d939b8e8f394f4e936b9c8847fe5 Mon Sep 17 00:00:00 2001
From: Omar Boukli-Hacene <oboukli@users.noreply.github.com>
Date: Tue, 18 Jul 2023 18:57:23 +0200
Subject: [PATCH] fix: Remove `constexpr` where invalid in C++20

---
 include/forfun/palindrome.hpp                         | 11 ++++-------
 include/forfun/palindromic_number.hpp                 |  2 +-
 .../project_euler/p0001_multiples_of_3_or_5.hpp       |  5 +++--
 src/palindromic_number.cpp                            |  2 +-
 4 files changed, 9 insertions(+), 11 deletions(-)

diff --git a/include/forfun/palindrome.hpp b/include/forfun/palindrome.hpp
index b759276..176d652 100644
--- a/include/forfun/palindrome.hpp
+++ b/include/forfun/palindrome.hpp
@@ -33,8 +33,7 @@ is_palindrome(std::string_view const& s) noexcept {
     return true;
 }
 
-[[nodiscard]] constexpr inline bool
-is_palindrome_ci(std::string_view const& s) noexcept {
+[[nodiscard]] inline bool is_palindrome_ci(std::string_view const& s) noexcept {
     auto const end{s.length() - 1};
     auto const mid{s.length() / 2};
 
@@ -68,8 +67,7 @@ is_palindrome(std::string_view const& s) noexcept {
     return true;
 }
 
-[[nodiscard]] constexpr inline bool
-is_palindrome_ci(std::string_view const& s) noexcept {
+[[nodiscard]] inline bool is_palindrome_ci(std::string_view const& s) noexcept {
     auto upper{s.cend() - 1};
     auto const mid{s.cbegin() + (s.length() / 2)};
 
@@ -98,15 +96,14 @@ is_palindrome(std::string_view const& s) noexcept {
 }
 
 namespace {
-[[nodiscard]] constexpr inline bool
+[[nodiscard]] inline bool
 equal_case_insensitive(char const a, char const b) noexcept {
     return std::tolower(static_cast<unsigned char>(a))
         == std::tolower(static_cast<unsigned char>(b));
 }
 } // namespace
 
-[[nodiscard]] constexpr inline bool
-is_palindrome_ci(std::string_view const& s) noexcept {
+[[nodiscard]] inline bool is_palindrome_ci(std::string_view const& s) noexcept {
     return std::equal(
         s.cbegin(), std::next(s.cbegin(), s.size() / 2), s.crbegin(),
         equal_case_insensitive);
diff --git a/include/forfun/palindromic_number.hpp b/include/forfun/palindromic_number.hpp
index daa48be..a6efb31 100644
--- a/include/forfun/palindromic_number.hpp
+++ b/include/forfun/palindromic_number.hpp
@@ -10,6 +10,6 @@
 #ifndef FORFUN_PALINDROMIC_NUMBER_HPP_
 #define FORFUN_PALINDROMIC_NUMBER_HPP_
 
-[[nodiscard]] bool is_palindrome(int const n) noexcept;
+[[nodiscard]] /* constexpr */ bool is_palindrome(int const n) noexcept;
 
 #endif // FORFUN_PALINDROMIC_NUMBER_HPP_
diff --git a/include/forfun/project_euler/p0001_multiples_of_3_or_5.hpp b/include/forfun/project_euler/p0001_multiples_of_3_or_5.hpp
index dbba9a3..ca7680e 100644
--- a/include/forfun/project_euler/p0001_multiples_of_3_or_5.hpp
+++ b/include/forfun/project_euler/p0001_multiples_of_3_or_5.hpp
@@ -19,14 +19,15 @@
 #include <algorithm>
 
 namespace {
-[[nodiscard]] inline constexpr int sum_2x(int const n, int const q) noexcept {
+[[nodiscard]] inline /* constexpr */ int
+sum_2x(int const n, int const q) noexcept {
     auto const d = std::div(n, q);
 
     return d.quot * (q + n - d.rem);
 }
 } // namespace
 
-[[nodiscard]] constexpr int find_sum_mult_three_five(int n) noexcept {
+[[nodiscard]] /* constexpr */ int find_sum_mult_three_five(int n) noexcept {
     --n;
 
     return (sum_2x(n, 3) + sum_2x(n, 5) - sum_2x(n, 15)) / 2;
diff --git a/src/palindromic_number.cpp b/src/palindromic_number.cpp
index bccbdf6..3a3019a 100644
--- a/src/palindromic_number.cpp
+++ b/src/palindromic_number.cpp
@@ -8,7 +8,7 @@
 
 #include <cstdlib>
 
-[[nodiscard]] bool is_palindrome(int const n) noexcept {
+[[nodiscard]] /* constexpr */ bool is_palindrome(int const n) noexcept {
     if (n < 0) {
         return false;
     }