From cb7cbf4cb3e3a12554a3c9dc1d291daab6bcf50b Mon Sep 17 00:00:00 2001
From: Mateusz Pusz <mateusz.pusz@gmail.com>
Date: Wed, 22 May 2024 12:18:48 +0200
Subject: [PATCH] refactor: `fixed_string` refactoring to match the R2 specs

---
 src/core/include/mp-units/ext/fixed_string.h | 53 ++++++++++++--------
 1 file changed, 32 insertions(+), 21 deletions(-)

diff --git a/src/core/include/mp-units/ext/fixed_string.h b/src/core/include/mp-units/ext/fixed_string.h
index 2b16d51b..05c12f4e 100644
--- a/src/core/include/mp-units/ext/fixed_string.h
+++ b/src/core/include/mp-units/ext/fixed_string.h
@@ -76,7 +76,7 @@ public:
   }
 
   // NOLINTNEXTLINE(google-explicit-constructor, hicpp-explicit-conversions)
-  consteval explicit(false) basic_fixed_string(const CharT (&txt)[N + 1])
+  consteval explicit(false) basic_fixed_string(const CharT (&txt)[N + 1]) noexcept
   {
     gsl_Expects(txt[N] == CharT{});
     for (std::size_t i = 0; i < N; ++i) data_[i] = txt[i];
@@ -139,13 +139,13 @@ public:
     gsl_Expects(!empty());
     return (*this)[N - 1];
   }
-  [[nodiscard]] constexpr const_pointer data() const noexcept { return static_cast<const_pointer>(data_); }
 
   // modifiers
   constexpr void swap(basic_fixed_string& s) noexcept { std::swap_ranges(begin(), end(), s.begin()); }
 
   // string operations
   [[nodiscard]] constexpr const_pointer c_str() const noexcept { return data(); }
+  [[nodiscard]] constexpr const_pointer data() const noexcept { return static_cast<const_pointer>(data_); }
   [[nodiscard]] constexpr std::basic_string_view<CharT, Traits> view() const noexcept
   {
     return std::basic_string_view<CharT, Traits>(cbegin(), cend());
@@ -160,47 +160,56 @@ public:
   [[nodiscard]] constexpr friend basic_fixed_string<CharT, N + N2, Traits> operator+(
     const basic_fixed_string& lhs, const basic_fixed_string<CharT, N2, Traits>& rhs) noexcept
   {
-    CharT txt[N + N2] = {};
-    for (size_t i = 0; i != N; ++i) txt[i] = lhs[i];
-    for (size_t i = 0; i != N2; ++i) txt[N + i] = rhs[i];
-    return basic_fixed_string<CharT, N + N2, Traits>(std::begin(txt), std::end(txt));
+    CharT txt[N + N2];
+    CharT* it = txt;
+    for (CharT c : lhs) *it++ = c;
+    for (CharT c : rhs) *it++ = c;
+    return basic_fixed_string<CharT, N + N2, Traits>(txt, it);
   }
 
   [[nodiscard]] constexpr friend basic_fixed_string<CharT, N + 1, Traits> operator+(const basic_fixed_string& lhs,
                                                                                     CharT rhs) noexcept
   {
-    CharT txt[N + 1] = {};
-    for (size_t i = 0; i != N; ++i) txt[i] = lhs[i];
-    txt[N] = rhs;
-    return basic_fixed_string<CharT, N + 1, Traits>(std::begin(txt), std::end(txt));
+    CharT txt[N + 1];
+    CharT* it = txt;
+    for (CharT c : lhs) *it++ = c;
+    *it++ = rhs;
+    return basic_fixed_string<CharT, N + 1, Traits>(txt, it);
   }
 
   [[nodiscard]] constexpr friend basic_fixed_string<CharT, 1 + N, Traits> operator+(
     const CharT lhs, const basic_fixed_string& rhs) noexcept
   {
-    CharT txt[1 + N] = {lhs};
-    for (size_t i = 0; i != N; ++i) txt[1 + i] = rhs[i];
-    return basic_fixed_string<CharT, 1 + N, Traits>(std::begin(txt), std::end(txt));
+    CharT txt[1 + N];
+    CharT* it = txt;
+    *it++ = lhs;
+    for (CharT c : rhs) *it++ = c;
+    return basic_fixed_string<CharT, 1 + N, Traits>(txt, it);
   }
 
   template<std::size_t N2>
   [[nodiscard]] consteval friend basic_fixed_string<CharT, N + N2 - 1, Traits> operator+(
     const basic_fixed_string& lhs, const CharT (&rhs)[N2]) noexcept
   {
-    CharT txt[N + N2 - 1] = {};
-    for (size_t i = 0; i != N; ++i) txt[i] = lhs[i];
-    for (size_t i = 0; i != N2 - 1; ++i) txt[N + i] = rhs[i];
-    return basic_fixed_string<CharT, N + N2 - 1, Traits>(std::begin(txt), std::end(txt));
+    gsl_Expects(rhs[N2 - 1] == CharT{});
+    CharT txt[N + N2];
+    CharT* it = txt;
+    for (CharT c : lhs) *it++ = c;
+    for (CharT c : rhs) *it++ = c;
+    return txt;
   }
 
   template<std::size_t N1>
   [[nodiscard]] consteval friend basic_fixed_string<CharT, N1 + N - 1, Traits> operator+(
     const CharT (&lhs)[N1], const basic_fixed_string& rhs) noexcept
   {
-    CharT txt[N1 + N - 1] = {};
-    for (size_t i = 0; i != N1 - 1; ++i) txt[i] = lhs[i];
-    for (size_t i = 0; i != N; ++i) txt[N1 - 1 + i] = rhs[i];
-    return basic_fixed_string<CharT, N1 + N - 1, Traits>(std::begin(txt), std::end(txt));
+    gsl_Expects(lhs[N1 - 1] == CharT{});
+    CharT txt[N1 + N];
+    CharT* it = txt;
+    for (size_t i = 0; i != N1 - 1; ++i) *it++ = lhs[i];
+    for (CharT c : rhs) *it++ = c;
+    *it++ = CharT();
+    return txt;
   }
 
   // non-member comparison functions
@@ -213,6 +222,7 @@ public:
   template<size_t N2>
   [[nodiscard]] friend consteval bool operator==(const basic_fixed_string& lhs, const CharT (&rhs)[N2])
   {
+    gsl_Expects(rhs[N2 - 1] == CharT{});
     return lhs.view() == std::basic_string_view<CharT, Traits>(std::cbegin(rhs), std::cend(rhs) - 1);
   }
 
@@ -225,6 +235,7 @@ public:
   template<size_t N2>
   [[nodiscard]] friend consteval auto operator<=>(const basic_fixed_string& lhs, const CharT (&rhs)[N2])
   {
+    gsl_Expects(rhs[N2 - 1] == CharT{});
     return lhs.view() <=> std::basic_string_view<CharT, Traits>(std::cbegin(rhs), std::cend(rhs) - 1);
   }