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Don't copy non-const-iterable ranges

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This commit is contained in:
Victor Zverovich
2021-08-07 07:27:20 -07:00
parent d6e882ed84
commit 111de881fa
1 changed files with 8 additions and 29 deletions
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37
include/fmt/ranges.h
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@ -160,30 +160,6 @@ template <typename T>
struct is_range_<T, void> struct is_range_<T, void>
: std::integral_constant<bool, (has_const_begin_end<T>::value || : std::integral_constant<bool, (has_const_begin_end<T>::value ||
has_mutable_begin_end<T>::value)> {}; has_mutable_begin_end<T>::value)> {};
template <typename T, typename Enable = void> struct range_to_view;
template <typename T>
struct range_to_view<T, enable_if_t<has_const_begin_end<T>::value>> {
struct view_t {
const T* m_range_ptr;
auto begin() const FMT_DECLTYPE_RETURN(detail::range_begin(*m_range_ptr));
auto end() const FMT_DECLTYPE_RETURN(detail::range_end(*m_range_ptr));
};
static auto view(const T& range) -> view_t { return {&range}; }
};
template <typename T>
struct range_to_view<T, enable_if_t<!has_const_begin_end<T>::value &&
has_mutable_begin_end<T>::value>> {
struct view_t {
T m_range_copy;
auto begin() FMT_DECLTYPE_RETURN(detail::range_begin(m_range_copy));
auto end() FMT_DECLTYPE_RETURN(detail::range_end(m_range_copy));
};
static auto view(const T& range) -> view_t { return {range}; }
};
# undef FMT_DECLTYPE_RETURN # undef FMT_DECLTYPE_RETURN
#endif #endif
@ -347,13 +323,16 @@ struct formatter<
return formatting.parse(ctx); return formatting.parse(ctx);
} }
template <typename FormatContext> template <
typename FormatContext::iterator format(const T& values, FormatContext& ctx) { typename FormatContext, typename U,
FMT_ENABLE_IF(
std::is_same<U, conditional_t<detail::has_const_begin_end<T>::value,
const T, T>>::value)>
auto format(U& values, FormatContext& ctx) -> decltype(ctx.out()) {
auto out = detail::copy(formatting.prefix, ctx.out()); auto out = detail::copy(formatting.prefix, ctx.out());
size_t i = 0; size_t i = 0;
auto view = detail::range_to_view<T>::view(values); auto it = detail::range_begin(values);
auto it = view.begin(); auto end = detail::range_end(values);
auto end = view.end();
for (; it != end; ++it) { for (; it != end; ++it) {
if (i > 0) out = detail::write_delimiter(out); if (i > 0) out = detail::write_delimiter(out);
out = detail::write_range_entry<Char>(out, *it); out = detail::write_range_entry<Char>(out, *it);