Implement natural_less as a customization point (issue #81)

The default version works with any forward sequence of char, including
std::string, std::vector<char> or char[]. It might work with other types
of characters than char, but it isn't guaranteed since it uses
std::isdigit.

include/cpp-sort/comparators/natural_less.h

@@ -0,0 +1,139 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2016 Morwenn
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+#ifndef CPPSORT_COMPARATORS_NATURAL_LESS_H_
+#define CPPSORT_COMPARATORS_NATURAL_LESS_H_
+
+////////////////////////////////////////////////////////////
+// Headers
+////////////////////////////////////////////////////////////
+#include <cctype>
+#include <iterator>
+#include <utility>
+#include <cpp-sort/utility/static_const.h>
+
+namespace cppsort
+{
+    namespace detail
+    {
+        ////////////////////////////////////////////////////////////
+        // Natural order for char sequences
+
+        template<typename ForwardIterator>
+        auto natural_less_impl(ForwardIterator begin1, ForwardIterator end1,
+                               ForwardIterator begin2, ForwardIterator end2)
+            -> bool
+        {
+            while (begin1 != end1 && begin2 != end2) {
+                auto last1 = begin1;
+                auto last2 = begin2;
+                do {
+                    if (not std::isdigit(*last1)) break;
+                    ++last1;
+                } while (last1 != end1);
+                do {
+                    if (not std::isdigit(*last2)) break;
+                    ++last2;
+                } while (last2 != end2);
+
+                if (last1 != begin1 && last2 != begin2) {
+                    // Skip leading zeros
+                    do {
+                        if (*begin1 != '0') break;
+                        ++begin1;
+                    } while (begin1 != last1);
+                    do {
+                        if (*begin2 != '0') break;
+                        ++begin2;
+                    } while (begin2 != last2);
+
+                    // Compare numbers
+                    auto size1 = std::distance(begin1, last1);
+                    auto size2 = std::distance(begin2, last2);
+                    if (size1 != size2) {
+                        return size1 < size2;
+                    }
+                    if (size1 == 0) {
+                        return false;
+                    }
+
+                    // Sizes are equal and not 0
+                    while (begin1 != end1) {
+                        if (*begin1 != *begin2) {
+                            return *begin1 < *begin2;
+                        }
+                        ++begin1;
+                        ++begin2;
+                    }
+                }
+
+                if (begin1 == end1) {
+                    return begin2 != end2;
+                }
+                if (begin2 == end2) {
+                    return false;
+                }
+
+                if (*begin1 != *begin2) {
+                    return *begin1 < *begin2;
+                }
+
+                ++begin1;
+                ++begin2;
+            }
+
+            return begin1 == end1 && begin2 != end2;
+        }
+
+        template<typename T>
+        auto natural_less(const T& lhs, const T& rhs)
+            -> bool
+        {
+            return natural_less_impl(std::begin(lhs), std::end(lhs),
+                                     std::begin(rhs), std::end(rhs));
+        }
+
+        ////////////////////////////////////////////////////////////
+        // Customization point
+
+        struct natural_less_fn
+        {
+            template<typename T, typename U>
+            constexpr auto operator()(T&& lhs, U&& rhs) const
+                noexcept(noexcept(natural_less(std::forward<T>(lhs), std::forward<U>(rhs))))
+                -> decltype(natural_less(std::forward<T>(lhs), std::forward<U>(rhs)))
+            {
+                return natural_less(std::forward<T>(lhs), std::forward<U>(rhs));
+            }
+        };
+    }
+
+    namespace
+    {
+        constexpr auto&& natural_less = utility::static_const<
+            detail::natural_less_fn
+        >::value;
+    }
+}
+
+#endif // CPPSORT_COMPARATORS_NATURAL_LESS_H_

testsuite/CMakeLists.txt

@@ -28,6 +28,7 @@ set(
 set(
     COMPARATORS_TESTS
 
+    comparators/natural_less.cpp
     comparators/total_less.cpp
 )
 

testsuite/comparators/natural_less.cpp

@@ -0,0 +1,54 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2016 Morwenn
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+#include <array>
+#include <string>
+#include <catch.hpp>
+#include <cpp-sort/comparators/natural_less.h>
+#include <cpp-sort/sort.h>
+
+TEST_CASE( "string natural sort with natural_less" )
+{
+    std::array<std::string, 7> array = {
+        "Yay",
+        "Yay 32 lol",
+        "Yuy 32 lol",
+        "Yay 045",
+        "Yay 01245 huhuhu",
+        "Yay 45",
+        "Yay 1234"
+    };
+    cppsort::sort(array, cppsort::natural_less);
+
+    std::array<std::string, 7> expected = {
+        "Yay",
+        "Yay 32 lol",
+        "Yay 45",
+        "Yay 045",
+        "Yay 1234",
+        "Yay 01245 huhuhu",
+        "Yuy 32 lol"
+    };
+    CHECK( array == expected );
+}
+