Replace static_const with inline constexpr variables (#66)

Author: Morwenn

README.md

@@ -171,7 +171,6 @@ in [Boost.Sort](https://www.boost.org/doc/libs/1_80_0/libs/sort/doc/html/index.h
 by Francisco Jose Tapia.
 
 * [`utility::as_function`](https://github.com/Morwenn/cpp-sort/wiki/Miscellaneous-utilities#as_function),
-[`utility::static_const`](https://github.com/Morwenn/cpp-sort/wiki/Miscellaneous-utilities#static_const),
 and several projection-enhanced helper algorithms come from Eric Niebler's [Range
 v3](https://github.com/ericniebler/range-v3) library. Several ideas such as proxy
 iterators, customization points and projections, as well as a few other utility

docs/Miscellaneous-utilities.md

@@ -531,34 +531,12 @@ auto swap_index_pairs_force_unroll(RandomAccessIterator first,
 
 *New in version 1.11.0*
 
-### `static_const`
-
-```cpp
-#include <cpp-sort/utility/static_const.h>
-```
-
-***WARNING:** `utility::static_const` is removed in version 2.0.0, use [`inline` variables][inline-variables] instead.*
-
-`static_const` is a tiny utility used to instantiate function objects (for example sorters) and expose a single global instance to users of the library while avoiding ODR problems. It is taken straight from [Range-v3][range-v3]. The general pattern to instantiate function objects is as follows:
-
-```cpp
-namespace
-{
-    constexpr auto&& awesome_sort
-        = cppsort::utility::static_const<awesome_sorter>::value;
-}
-```
-
-You can read more about this instantiation pattern in [this article][eric-niebler-static-const] by Eric Niebler.
-
 
   [apply-permutation]: Miscellaneous-utilities.md#apply_permutation
   [chainable-projections]: Chainable-projections.md
   [callable]: https://en.cppreference.com/w/cpp/named_req/Callable
   [ebo]: https://en.cppreference.com/w/cpp/language/ebo
-  [eric-niebler-static-const]: https://ericniebler.com/2014/10/21/customization-point-design-in-c11-and-beyond/
   [fixed-size-sorters]: Fixed-size-sorters.md
-  [inline-variables]: https://en.cppreference.com/w/cpp/language/inline
   [is-stable]: Sorter-traits.md#is_stable
   [metrics]: Metrics.md
   [numpy-argsort]: https://numpy.org/doc/stable/reference/generated/numpy.argsort.html

docs/Writing-a-bubble_sorter.md

@@ -393,19 +393,9 @@ We use forwarding references to ensure that the range overload works with lvalue
 The sorter abstraction is useful, but most of the time we only need a sorting algorithm. Therefore, it might be a good idea to instantiate `bubble_sorter` and to have a global `bubble_sort` instance, more versatile than the original `bubble_sort` algorithm.
 
 ```cpp
-// C++14
-namespace
-{
-    constexpr auto&& bubble_sort
-        = cppsort::utility::static_const<bubble_sorter>::value;
-}
-
-// C++17
 inline constexpr bubble_sorter bubble_sort{};
 ```
 
-The combination of [`utility::static_const`][utility-static-const] with an anonymous namespace is a trick used to avoid ODR problems; you can read more about how and why it works in [Eric Niebler's original article](https://ericniebler.com/2014/10/21/customization-point-design-in-c11-and-beyond/). It is basically a poor man's substitute to compensate the lack of `inline` variables pre-C++17.
-
 ## Better error messages
 
 We now have a versatile `bubble_sorter`, able to handle many scenarios, and optimized as much as a bubble sort can be without turning it into a different algorithm. It works really well... until it doesn't. **cpp-sort** has one major drawback there: when not used correctly, the error messages are often close to unreadable; forget one `const` and embrace the hundreds of lines of cryptic SFINAE error messages, and I really mean it!. The sorter works properly, but we can still somewhat improve the way it fails.
@@ -459,5 +449,4 @@ That's it: we have covered pretty much every interesting aspect of writing a sim
   [utility-identity]: Miscellaneous-utilities.md#miscellaneous-function-objects
   [utility-iter-move]: Miscellaneous-utilities.md#iter_move-and-iter_swap
   [utility-size]: Miscellaneous-utilities.md#size
-  [utility-static-const]: Miscellaneous-utilities.md#static_const
   [writing-a-sorter]: Writing-a-sorter.md

docs/Writing-a-sorter.md

@@ -63,7 +63,7 @@ Now, let's define a set of rules to apply when writing sorters. These rules don'
 
 **Rule 1.4:** *sorters* shall be immutable and every overload of `operator()` shall explicitly be marked `const` (make sure to check twice: forgetting to `const`-qualify them can cause hundreds of lines of cryptic error messages). Some parts of the library *may* accept mutable sorters, but that's never guaranteed unless specified otherwise.
 
-**Rule 1.5:** *sorter* implementers are encouraged but not required to provide a default instance of their *sorters* for convenience. `inline` variables (C++17) or the library's [`static_const`][static-const] utility (C++14) can be used to avoid ODR-related problems.
+**Rule 1.5:** *sorter* implementers are encouraged but not required to provide a default instance of their *sorters* for convenience. `inline` variables can be used to avoid ODR-related problems.
 
 ## Category of iterators
 
@@ -579,7 +579,6 @@ In the example above, the resulting sorter will use our `low_projections_sorter`
   [sqrtsort]: https://github.com/Mrrl/SqrtSort
   [stability]: https://en.wikipedia.org/wiki/Sorting_algorithm#Stability
   [stable-adapter]: Sorter-adapters.md#stable_adapter-make_stable-and-stable_t
-  [static-const]: Miscellaneous-utilities.md#static_const
   [std-array]: https://en.cppreference.com/w/cpp/container/array
   [std-greater-void]: https://en.cppreference.com/w/cpp/utility/functional/greater_void
   [std-identity]: https://en.cppreference.com/w/cpp/utility/functional/identity

examples/bubble_sorter.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015-2021 Morwenn
+ * Copyright (c) 2015-2025 Morwenn
  * SPDX-License-Identifier: MIT
  */
 #include <cstddef>
@@ -11,7 +11,6 @@
 #include <cpp-sort/utility/as_function.h>
 #include <cpp-sort/utility/iter_move.h>
 #include <cpp-sort/utility/size.h>
-#include <cpp-sort/utility/static_const.h>
 
 namespace detail
 {
@@ -95,11 +94,8 @@ struct bubble_sorter:
     cppsort::sorter_facade<detail::bubble_sorter_impl>
 {};
 
-namespace
-{
-    constexpr auto&& bubble_sort
-        = cppsort::utility::static_const<bubble_sorter>::value;
-}
+inline constexpr bubble_sorter bubble_sort{};
+
 
 #include <algorithm>
 #include <array>

include/cpp-sort/comparators/case_insensitive_less.h

@@ -13,7 +13,6 @@
 #include <locale>
 #include <type_traits>
 #include <utility>
-#include <cpp-sort/utility/static_const.h>
 #include "../detail/type_traits.h"
 
 namespace cppsort
@@ -271,12 +270,7 @@ namespace cppsort
 
     using case_insensitive_less_t = detail::case_insensitive_less_fn;
 
-    namespace
-    {
-        constexpr auto&& case_insensitive_less = utility::static_const<
-            detail::case_insensitive_less_fn
-        >::value;
-    }
+    inline constexpr detail::case_insensitive_less_fn case_insensitive_less{};
 }
 
 #endif // CPPSORT_COMPARATORS_CASE_INSENSITIVE_LESS_H_

include/cpp-sort/comparators/natural_less.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016-2019 Morwenn
+ * Copyright (c) 2016-2025 Morwenn
  * SPDX-License-Identifier: MIT
  */
 #ifndef CPPSORT_COMPARATORS_NATURAL_LESS_H_
@@ -11,7 +11,6 @@
 #include <cctype>
 #include <iterator>
 #include <utility>
-#include <cpp-sort/utility/static_const.h>
 
 namespace cppsort
 {
@@ -113,12 +112,7 @@ namespace cppsort
 
     using natural_less_t = detail::natural_less_fn;
 
-    namespace
-    {
-        constexpr auto&& natural_less = utility::static_const<
-            detail::natural_less_fn
-        >::value;
-    }
+    inline constexpr detail::natural_less_fn natural_less{};
 }
 
 #endif // CPPSORT_COMPARATORS_NATURAL_LESS_H_

include/cpp-sort/comparators/partial_greater.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016-2021 Morwenn
+ * Copyright (c) 2016-2025 Morwenn
  * SPDX-License-Identifier: MIT
  */
 #ifndef CPPSORT_COMPARATORS_PARTIAL_GREATER_H_
@@ -12,7 +12,6 @@
 #include <utility>
 #include <cpp-sort/comparators/weak_greater.h>
 #include <cpp-sort/utility/branchless_traits.h>
-#include <cpp-sort/utility/static_const.h>
 #include "../detail/type_traits.h"
 
 namespace cppsort
@@ -59,12 +58,7 @@ namespace cppsort
 
     using partial_greater_t = detail::partial_greater_fn;
 
-    namespace
-    {
-        constexpr auto&& partial_greater = utility::static_const<
-            detail::partial_greater_fn
-        >::value;
-    }
+    inline constexpr detail::partial_greater_fn partial_greater{};
 
     // Branchless traits
 

include/cpp-sort/comparators/partial_less.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016-2021 Morwenn
+ * Copyright (c) 2016-2025 Morwenn
  * SPDX-License-Identifier: MIT
  */
 #ifndef CPPSORT_COMPARATORS_PARTIAL_LESS_H_
@@ -12,7 +12,6 @@
 #include <utility>
 #include <cpp-sort/comparators/weak_less.h>
 #include <cpp-sort/utility/branchless_traits.h>
-#include <cpp-sort/utility/static_const.h>
 #include "../detail/type_traits.h"
 
 namespace cppsort
@@ -59,12 +58,7 @@ namespace cppsort
 
     using partial_less_t = detail::partial_less_fn;
 
-    namespace
-    {
-        constexpr auto&& partial_less = utility::static_const<
-            detail::partial_less_fn
-        >::value;
-    }
+    inline constexpr detail::partial_less_fn partial_less{};
 
     // Branchless traits
 

include/cpp-sort/comparators/total_greater.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016-2022 Morwenn
+ * Copyright (c) 2016-2025 Morwenn
  * SPDX-License-Identifier: MIT
  */
 #ifndef CPPSORT_COMPARATORS_TOTAL_GREATER_H_
@@ -12,7 +12,6 @@
 #include <type_traits>
 #include <utility>
 #include <cpp-sort/utility/branchless_traits.h>
-#include <cpp-sort/utility/static_const.h>
 #include "../detail/floating_point_weight.h"
 #include "../detail/type_traits.h"
 
@@ -68,12 +67,7 @@ namespace cppsort
 
     using total_greater_t = detail::total_greater_fn;
 
-    namespace
-    {
-        constexpr auto&& total_greater = utility::static_const<
-            detail::total_greater_fn
-        >::value;
-    }
+    inline constexpr detail::total_greater_fn total_greater{};
 
     // Branchless traits