traits: add is_contiguous query for containers

test/traits.cpp

@@ -1,6 +1,8 @@
 #include <cruft/util/tap.hpp>
 #include <cruft/util/types/traits.hpp>
 
+#include <list>
+
 
 ///////////////////////////////////////////////////////////////////////////////
 template <typename FuncT>
@@ -56,4 +58,10 @@ main (void)
                 "complex function type");
 
     tap.expect (!has_return_type<int>::value, "integer is not applicable to func_traits");
+
+
+    tap.expect (is_contiguous_v<std::vector<char>>, "vector is contiguous");
+    tap.expect (is_contiguous_v<std::array<char,4>>, "array is contiguous");
+    tap.expect (!is_contiguous_v<std::list<char>>, "list is not contiguous");
+    return tap.status ();
 }

types/traits.hpp

@@ -270,4 +270,24 @@ template <std::size_t N, typename FuncT>
 using nth_argument_t = typename nth_argument<N, FuncT>::type;
 
 
+///////////////////////////////////////////////////////////////////////////////
+#include <string>
+#include <array>
+#include <vector>
+
+template <typename T>
+struct is_contiguous : public std::false_type {};
+
+template <typename CharT, typename Traits, typename Allocator>
+struct is_contiguous<std::basic_string<CharT, Traits, Allocator>> : public std::true_type {};
+
+template <typename T, std::size_t N>
+struct is_contiguous<std::array<T,N>>: public std::true_type {};
+
+template <typename T, typename Allocator>
+struct is_contiguous<std::vector<T,Allocator>>: public std::true_type {};
+
+template <typename T>
+constexpr auto is_contiguous_v = is_contiguous<T>::value;
+
 #endif