refactor: explicit usage unified accross the library

docs/use_cases/custom_representation_types.rst

@@ -36,7 +36,7 @@ The simplest representation type that fulfills the above requirements can look a
       std::intmax_t value_;
     public:
       my_rep() = default;
-      explicit constexpr my_rep(std::intmax_t v) noexcept : value_(v) {}
+      constexpr explicit my_rep(std::intmax_t v) noexcept : value_(v) {}
 
       [[nodiscard]] bool operator==(my_rep) const = default;
 

src/include/units/bits/external/fixed_string.h

@@ -43,9 +43,9 @@ struct basic_fixed_string {
   using iterator = CharT*;
   using const_iterator = const CharT*;
 
-  constexpr basic_fixed_string(CharT ch) noexcept { data_[0] = ch; }
+  constexpr explicit(false) basic_fixed_string(CharT ch) noexcept { data_[0] = ch; }
 
-  constexpr basic_fixed_string(const CharT (&txt)[N + 1]) noexcept
+  constexpr explicit(false) basic_fixed_string(const CharT (&txt)[N + 1]) noexcept
   {
     if constexpr (N != 0)
       for (std::size_t i = 0; i < N; ++i) data_[i] = txt[i];

src/include/units/quantity.h

@@ -133,15 +133,15 @@ public:
   quantity(quantity&&) = default;
 
   template<safe_convertible_to_<rep> Value>
-  explicit(!(is_same_v<dimension, dim_one> && is_same_v<unit, ::units::one>))
-  constexpr quantity(const Value& v) : value_(v) {}
+  constexpr explicit(!(is_same_v<dimension, dim_one> && is_same_v<unit, ::units::one>))
+  quantity(const Value& v) : value_(v) {}
 
   template<safe_castable_to_<quantity> Q>
-  constexpr quantity(const Q& q) : value_(quantity_cast<quantity>(q).count()) {}
+  constexpr explicit(false) quantity(const Q& q) : value_(quantity_cast<quantity>(q).count()) {}
 
   template<QuantityLike Q>
     requires safe_castable_to_<quantity_like_type<Q>, quantity>
-  explicit constexpr quantity(const Q& q) : quantity(quantity_like_type<Q>(quantity_like_traits<Q>::count(q))) {}
+  constexpr explicit quantity(const Q& q) : quantity(quantity_like_type<Q>(quantity_like_traits<Q>::count(q))) {}
 
   quantity& operator=(const quantity&) = default;
   quantity& operator=(quantity&&) = default;

src/include/units/quantity_point.h

@@ -70,7 +70,7 @@ public:
 
   template<QuantityPoint QP2>
     requires std::is_convertible_v<typename QP2::quantity_type, quantity_type>
-  constexpr quantity_point(const QP2& qp) : q_{qp.relative()} {}
+  constexpr explicit(false) quantity_point(const QP2& qp) : q_{qp.relative()} {}
 
   quantity_point& operator=(const quantity_point&) = default;
   quantity_point& operator=(quantity_point&&) = default;

src/include/units/ratio.h

@@ -51,7 +51,7 @@ struct ratio {
   std::intmax_t den;
   std::intmax_t exp;
 
-  explicit constexpr ratio(std::intmax_t n, std::intmax_t d = 1, std::intmax_t e = 0): num(n), den(d), exp(e)
+  constexpr explicit ratio(std::intmax_t n, std::intmax_t d = 1, std::intmax_t e = 0): num(n), den(d), exp(e)
   {
     gsl_Expects(den != 0);
     detail::normalize(num, den, exp);

test/unit_test/static/custom_rep_test_min_expl.cpp

@@ -44,7 +44,7 @@ public:
   min_expl() requires (Mode != 1) = default;
 
   // construction from std::int64_t
-  explicit constexpr min_expl(std::intmax_t v) noexcept requires (Mode != 2) : value_(v) {}
+  constexpr explicit min_expl(std::intmax_t v) noexcept requires (Mode != 2) : value_(v) {}
 
   // copy construction
   min_expl(const min_expl&) requires (Mode != 3) = default;