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Fix format_as for non-const begin/end views (#3955)

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base::format does not accept rvalues, using the result of format_as
directly means it is passed one. Doesn't matter for ranges with a const
begin and end, but filter_view caches, so it only has mutable begin/end.
Use auto&& to avoid copy if format_as returns const ref
This commit is contained in:
Justin Riddell
2024-05-13 17:35:55 +01:00
committed by GitHub
parent 1f436c646e
commit 8e728044f6
2 changed files with 45 additions and 6 deletions
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4
include/fmt/format.h
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@ -4000,7 +4000,9 @@ struct formatter<T, Char, enable_if_t<detail::has_format_as<T>::value>>
template <typename FormatContext> template <typename FormatContext>
auto format(const T& value, FormatContext& ctx) const -> decltype(ctx.out()) { auto format(const T& value, FormatContext& ctx) const -> decltype(ctx.out()) {
using base = formatter<detail::format_as_t<T>, Char>; using base = formatter<detail::format_as_t<T>, Char>;
return base::format(format_as(value), ctx); // format functions expect lvalue refs, not rvalues
auto&& val = format_as(value);
return base::format(val, ctx);
} }
}; };

47
test/ranges-test.cc
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@ -7,6 +7,7 @@
#include "fmt/ranges.h" #include "fmt/ranges.h"
#include <array>
#include <list> #include <list>
#include <map> #include <map>
#include <numeric> #include <numeric>
@ -654,18 +655,18 @@ TEST(ranges_test, lvalue_qualified_begin_end) {
} }
#if !defined(__cpp_lib_ranges) || __cpp_lib_ranges <= 202106L #if !defined(__cpp_lib_ranges) || __cpp_lib_ranges <= 202106L
# define ENABLE_INPUT_RANGE_JOIN_TEST 0 # define ENABLE_STD_VIEWS_TESTS 0
#elif FMT_CLANG_VERSION #elif FMT_CLANG_VERSION
# if FMT_CLANG_VERSION > 1500 # if FMT_CLANG_VERSION > 1500
# define ENABLE_INPUT_RANGE_JOIN_TEST 1 # define ENABLE_STD_VIEWS_TESTS 1
# else # else
# define ENABLE_INPUT_RANGE_JOIN_TEST 0 # define ENABLE_STD_VIEWS_TESTS 0
# endif # endif
#else #else
# define ENABLE_INPUT_RANGE_JOIN_TEST 1 # define ENABLE_STD_VIEWS_TESTS 1
#endif #endif
#if ENABLE_INPUT_RANGE_JOIN_TEST #if ENABLE_STD_VIEWS_TESTS
TEST(ranges_test, input_range_join) { TEST(ranges_test, input_range_join) {
auto iss = std::istringstream("1 2 3 4 5"); auto iss = std::istringstream("1 2 3 4 5");
auto view = std::views::istream<std::string>(iss); auto view = std::views::istream<std::string>(iss);
@ -679,6 +680,42 @@ TEST(ranges_test, input_range_join_overload) {
"1.2.3.4.5", "1.2.3.4.5",
fmt::format("{}", fmt::join(std::views::istream<std::string>(iss), "."))); fmt::format("{}", fmt::join(std::views::istream<std::string>(iss), ".")));
} }
namespace views_filter_view_test {
struct codec_mask {
static constexpr auto kCodecs = std::array{0, 1, 2, 3};
int except{};
};
auto format_as(codec_mask mask) {
// Careful not to capture param by reference here, it will dangle
return codec_mask::kCodecs |
std::views::filter([mask](auto c) { return c != mask.except; });
}
} // namespace views_filter_view_test
TEST(ranges_test, format_as_with_ranges_mutable_begin_end) {
using namespace views_filter_view_test;
{
auto make_filter_view = []() {
return codec_mask::kCodecs |
std::views::filter([](auto c) { return c != 2; });
};
auto r = make_filter_view();
EXPECT_EQ("[0, 1, 3]", fmt::format("{}", r));
EXPECT_EQ("[0, 1, 3]", fmt::format("{}", make_filter_view()));
}
{
const codec_mask const_mask{2};
codec_mask mask{2};
EXPECT_EQ("[0, 1, 3]", fmt::format("{}", const_mask));
EXPECT_EQ("[0, 1, 3]", fmt::format("{}", mask));
EXPECT_EQ("[0, 1, 3]", fmt::format("{}", codec_mask{2}));
}
}
#endif #endif
TEST(ranges_test, std_istream_iterator_join) { TEST(ranges_test, std_istream_iterator_join) {