From 9cf44150e537e5d200dde3688286d7a494e4cda3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Rimas=20Misevi=C4=8Dius?= <rmisev3@gmail.com>
Date: Sat, 4 Nov 2023 20:51:50 +0200
Subject: [PATCH] Add `constexpr` to some `str_view` class member functions
 (#23)

* add UPA_CONSTEXPR_14 macro

* add workflow to compile with g++ using C++14
---
 .github/workflows/test-ubuntu.yml |  5 +++++
 include/upa/config.h              |  6 +++++-
 include/upa/str_view.h            | 32 +++++++++++++++++--------------
 3 files changed, 28 insertions(+), 15 deletions(-)

diff --git a/.github/workflows/test-ubuntu.yml b/.github/workflows/test-ubuntu.yml
index 8f004420..bfdbd363 100644
--- a/.github/workflows/test-ubuntu.yml
+++ b/.github/workflows/test-ubuntu.yml
@@ -53,6 +53,11 @@ jobs:
             cmake_options: "-DURL_AMALGAMATED=ON -DURL_BUILD_EXAMPLES=ON"
             before_cmake: tools/amalgamate.sh
 
+          - name: g++-9 C++14
+            cxx_compiler: g++-9
+            cxx_standard: 14
+            cmake_options: "-DURL_BUILD_EXAMPLES=ON"
+
           - name: g++-9 C++11
             cxx_compiler: g++-9
             cxx_standard: 11
diff --git a/include/upa/config.h b/include/upa/config.h
index 3fa19a61..f225287a 100644
--- a/include/upa/config.h
+++ b/include/upa/config.h
@@ -31,8 +31,12 @@
 #endif
 
 // Define UPA_CPP_14 if compiler supports C++14 or later
-#if defined(_MSVC_LANG) ? (_MSVC_LANG >= 201402) : (__cplusplus >= 201402)
+// Note: Visual Studio 2015 (14.0; _MSC_VER == 1900) lacks sufficient C++14 support
+#if defined(_MSVC_LANG) ? (_MSVC_LANG >= 201402 && _MSC_VER > 1900) : (__cplusplus >= 201402)
 # define UPA_CPP_14
+# define UPA_CONSTEXPR_14 constexpr
+#else
+# define UPA_CONSTEXPR_14 inline
 #endif
 
 #endif // UPA_CONFIG_H
diff --git a/include/upa/str_view.h b/include/upa/str_view.h
index 4a3cae77..0281df5a 100644
--- a/include/upa/str_view.h
+++ b/include/upa/str_view.h
@@ -6,12 +6,16 @@
 #ifndef UPA_STR_VIEW_H
 #define UPA_STR_VIEW_H
 
+#include "config.h"
 #include <algorithm>
 #include <string>
 #include <type_traits>
 
 namespace upa {
 
+/// @brief A very simplified implementation of the basic_string_view
+///
+/// It is used when compiling with C++11 or C++14 compilers.
 template<typename CharT, typename Traits = std::char_traits<CharT>>
 class str_view {
 public:
@@ -31,41 +35,41 @@ class str_view {
     // static constexpr size_type npos = size_type(-1);
 
     // constructors
-    str_view() noexcept = default;
-    str_view(const str_view&) noexcept = default;
-    str_view(const CharT* ptr, size_type len) : ptr_(ptr), len_(len) {}
+    constexpr str_view() noexcept = default;
+    constexpr str_view(const str_view&) noexcept = default;
+    constexpr str_view(const CharT* ptr, size_type len) : ptr_(ptr), len_(len) {}
     str_view(const CharT* ptr) : ptr_(ptr), len_(Traits::length(ptr)) {}
 
     // assignment
-    str_view& operator=(const str_view&) noexcept = default;
+    UPA_CONSTEXPR_14 str_view& operator=(const str_view&) noexcept = default;
 
     // destructor
     ~str_view() noexcept = default;
 
     // iterator support
-    const_iterator begin() const noexcept { return ptr_; }
-    const_iterator end() const noexcept { return ptr_ + len_; }
+    constexpr const_iterator begin() const noexcept { return ptr_; }
+    constexpr const_iterator end() const noexcept { return ptr_ + len_; }
 
     // capacity
-    size_type size() const noexcept { return len_; }
-    size_type length() const noexcept { return len_; }
-    bool empty() const noexcept { return len_ == 0; }
+    constexpr size_type size() const noexcept { return len_; }
+    constexpr size_type length() const noexcept { return len_; }
+    constexpr bool empty() const noexcept { return len_ == 0; }
 
     // element access
-    const_reference operator[](size_type ind) const {
+    constexpr const_reference operator[](size_type ind) const {
         return ptr_[ind];
     }
-    const_pointer data() const noexcept { return ptr_; }
+    constexpr const_pointer data() const noexcept { return ptr_; }
 
     // modifiers
-    void remove_prefix(size_type n) {
+    UPA_CONSTEXPR_14 void remove_prefix(size_type n) {
         ptr_ += n;
         len_ -= n;
     }
-    void remove_suffix(size_type n) {
+    UPA_CONSTEXPR_14 void remove_suffix(size_type n) {
         len_ -= n;
     }
-    void swap(str_view& x) noexcept {
+    UPA_CONSTEXPR_14 void swap(str_view& x) noexcept {
         const str_view tmp{x};
         x = *this;
         *this = tmp;