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Provide reasonable default definition for is_contiguous

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Signed-off-by: Vladislav Shchapov <vladislav@shchapov.ru>
This commit is contained in:
Vladislav Shchapov 2026-05-14 00:38:26 +05:00
parent 2f18a88e68
commit 83c3684a8e
2 changed files with 24 additions and 1 deletions
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15
include/fmt/base.h
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@ -593,7 +593,20 @@ template <typename T> class basic_appender;
using appender = basic_appender<char>;
// Checks whether T is a container with contiguous storage.
template <typename T> struct is_contiguous : std::false_type {};
namespace detail {
template <typename T, typename Enable = void>
struct is_contiguous_ : std::false_type {};
template <typename T>
struct is_contiguous_<T, void_t<decltype(std::declval<T&>().data()),
decltype(std::declval<T&>().size()),
decltype(std::declval<T&>()[size_t{}])>>
: std::true_type {};
} // namespace detail
template <typename T> struct is_contiguous : detail::is_contiguous_<T> {};
class context;
template <typename OutputIt, typename Char> class generic_context;

10
test/base-test.cc
View File

@ -21,8 +21,10 @@
#include <functional> // std::equal_to
#include <iterator> // std::back_insert_iterator, std::distance
#include <limits> // std::numeric_limits
#include <list> // std::list
#include <string> // std::string
#include <type_traits> // std::is_same
#include <vector> // std::vector
#include "gmock/gmock.h"
@ -876,6 +878,14 @@ FMT_BEGIN_NAMESPACE
template <> struct is_contiguous<custom_container> : std::true_type {};
FMT_END_NAMESPACE
TEST(base_test, is_contiguous) {
EXPECT_TRUE((fmt::is_contiguous<custom_container>::value));
EXPECT_TRUE((fmt::is_contiguous<std::string>::value));
EXPECT_TRUE((fmt::is_contiguous<fmt::string_view>::value));
EXPECT_TRUE((fmt::is_contiguous<std::vector<char>>::value));
EXPECT_FALSE((fmt::is_contiguous<std::list<char>>::value));
}
TEST(base_test, format_to_custom_container) {
auto c = custom_container();
fmt::format_to(std::back_inserter(c), "");