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Enable fmt::join for uncopyable iterators
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If iterator not copyable mutate the underlying iterator
Notably std::ranges::basic_istream_view::__iterator
Addresses issue (#3802)
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Arghnews committed May 5, 2024
1 parent 16cec4f commit 7013466
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Showing 2 changed files with 73 additions and 4 deletions.
24 changes: 20 additions & 4 deletions include/fmt/ranges.h
Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@
# include <iterator>
# include <tuple>
# include <type_traits>
# include <utility>
#endif

#include "format.h"
Expand Down Expand Up @@ -611,7 +612,7 @@ struct join_view : detail::view {
basic_string_view<Char> sep;

join_view(It b, Sentinel e, basic_string_view<Char> s)
: begin(b), end(e), sep(s) {}
: begin(std::move(b)), end(e), sep(s) {}
};

template <typename It, typename Sentinel, typename Char>
Expand All @@ -631,10 +632,25 @@ struct formatter<join_view<It, Sentinel, Char>, Char> {
return value_formatter_.parse(ctx);
}

template <typename FormatContext>
auto format(const join_view<It, Sentinel, Char>& value,
template <typename FormatContext, typename Iter,
FMT_ENABLE_IF(std::is_copy_constructible<Iter>::value)>
auto format(const join_view<Iter, Sentinel, Char>& value,
FormatContext& ctx) const -> decltype(ctx.out()) {
auto it = value.begin;
return do_format(value, ctx, it);
}

template <typename FormatContext, typename Iter,
FMT_ENABLE_IF(!std::is_copy_constructible<Iter>::value)>
auto format(join_view<Iter, Sentinel, Char>& value, FormatContext& ctx) const
-> decltype(ctx.out()) {
return do_format(value, ctx, value.begin);
}

private:
template <typename FormatContext>
auto do_format(const join_view<It, Sentinel, Char>& value,
FormatContext& ctx, It& it) const -> decltype(ctx.out()) {
auto out = ctx.out();
if (it != value.end) {
out = value_formatter_.format(*it, ctx);
Expand All @@ -656,7 +672,7 @@ struct formatter<join_view<It, Sentinel, Char>, Char> {
*/
template <typename It, typename Sentinel>
auto join(It begin, Sentinel end, string_view sep) -> join_view<It, Sentinel> {
return {begin, end, sep};
return {std::move(begin), end, sep};
}

/**
Expand Down
53 changes: 53 additions & 0 deletions test/ranges-test.cc
Original file line number Diff line number Diff line change
Expand Up @@ -652,3 +652,56 @@ struct lvalue_qualified_begin_end {
TEST(ranges_test, lvalue_qualified_begin_end) {
EXPECT_EQ(fmt::format("{}", lvalue_qualified_begin_end{}), "[1, 2, 3, 4, 5]");
}

#if !defined(__cpp_lib_ranges) || __cpp_lib_ranges <= 202106L
# define ENABLE_INPUT_RANGE_JOIN_TEST 0
#elif FMT_CLANG_VERSION
# if FMT_CLANG_VERSION > 1500
# define ENABLE_INPUT_RANGE_JOIN_TEST 1
# else
# define ENABLE_INPUT_RANGE_JOIN_TEST 0
# endif
#else
# define ENABLE_INPUT_RANGE_JOIN_TEST 1
#endif

#if ENABLE_INPUT_RANGE_JOIN_TEST
TEST(ranges_test, input_range_join) {
std::istringstream iss("1 2 3 4 5");
auto view = std::views::istream<std::string>(iss);
auto joined_view = fmt::join(view.begin(), view.end(), ", ");
EXPECT_EQ("1, 2, 3, 4, 5", fmt::format("{}", std::move(joined_view)));
}

TEST(ranges_test, input_range_join_overload) {
std::istringstream iss("1 2 3 4 5");
EXPECT_EQ(
"1.2.3.4.5",
fmt::format("{}", fmt::join(std::views::istream<std::string>(iss), ".")));
}
#endif

TEST(ranges_test, std_istream_iterator_join) {
std::istringstream iss("1 2 3 4 5");
std::istream_iterator<int> first{iss};
std::istream_iterator<int> last{};
auto joined_view = fmt::join(first, last, ", ");
EXPECT_EQ("1, 2, 3, 4, 5", fmt::format("{}", std::move(joined_view)));
}

TEST(ranges_test, movable_only_istream_iter_join) {
// Mirrors c++20 std::ranges::basic_istream_view::iterator
struct UncopyableIstreamIter : std::istream_iterator<int> {
explicit UncopyableIstreamIter(std::istringstream& iss)
: std::istream_iterator<int>{iss} {}
UncopyableIstreamIter(const UncopyableIstreamIter&) = delete;
UncopyableIstreamIter(UncopyableIstreamIter&&) = default;
};
static_assert(!std::is_copy_constructible<UncopyableIstreamIter>::value, "");

std::istringstream iss("1 2 3 4 5");
UncopyableIstreamIter first{iss};
std::istream_iterator<int> last{};
auto joined_view = fmt::join(std::move(first), last, ", ");
EXPECT_EQ("1, 2, 3, 4, 5", fmt::format("{}", std::move(joined_view)));
}

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