diff options
Diffstat (limited to 'absl/strings/internal/str_join_internal.h')
-rw-r--r-- | absl/strings/internal/str_join_internal.h | 57 |
1 files changed, 26 insertions, 31 deletions
diff --git a/absl/strings/internal/str_join_internal.h b/absl/strings/internal/str_join_internal.h index e73f1dde403d..c5fdc287cbab 100644 --- a/absl/strings/internal/str_join_internal.h +++ b/absl/strings/internal/str_join_internal.h @@ -31,13 +31,15 @@ #ifndef ABSL_STRINGS_INTERNAL_STR_JOIN_INTERNAL_H_ #define ABSL_STRINGS_INTERNAL_STR_JOIN_INTERNAL_H_ -#include <cassert> +#include <cstring> #include <iterator> #include <memory> #include <string> +#include <type_traits> #include <utility> #include "absl/strings/internal/ostringstream.h" +#include "absl/strings/internal/resize_uninitialized.h" #include "absl/strings/str_cat.h" namespace absl { @@ -202,28 +204,9 @@ std::string JoinAlgorithm(Iterator start, Iterator end, absl::string_view s, return result; } -// No-op placeholder for input iterators which can not be iterated over. -template <typename Iterator> -size_t GetResultSize(Iterator, Iterator, size_t, std::input_iterator_tag) { - return 0; -} - -// Calculates space to reserve, if the iterator supports multiple passes. -template <typename Iterator> -size_t GetResultSize(Iterator it, Iterator end, size_t separator_size, - std::forward_iterator_tag) { - assert(it != end); - size_t length = it->size(); - while (++it != end) { - length += separator_size; - length += it->size(); - } - return length; -} - -// A joining algorithm that's optimized for an iterator range of std::string-like -// objects that do not need any additional formatting. This is to optimize the -// common case of joining, say, a std::vector<std::string> or a +// A joining algorithm that's optimized for a forward iterator range of +// std::string-like objects that do not need any additional formatting. This is to +// optimize the common case of joining, say, a std::vector<std::string> or a // std::vector<absl::string_view>. // // This is an overload of the previous JoinAlgorithm() function. Here the @@ -236,20 +219,32 @@ size_t GetResultSize(Iterator it, Iterator end, size_t separator_size, // std::string to avoid the need to resize while appending. To do this, the iterator // range will be traversed twice: once to calculate the total needed size, and // then again to copy the elements and delimiters to the output std::string. -template <typename Iterator> +template <typename Iterator, + typename = typename std::enable_if<std::is_convertible< + typename std::iterator_traits<Iterator>::iterator_category, + std::forward_iterator_tag>::value>::type> std::string JoinAlgorithm(Iterator start, Iterator end, absl::string_view s, NoFormatter) { std::string result; if (start != end) { - typename std::iterator_traits<Iterator>::iterator_category iterator_tag; - result.reserve(GetResultSize(start, end, s.size(), iterator_tag)); + // Sums size + size_t result_size = start->size(); + for (Iterator it = start; ++it != end;) { + result_size += s.size(); + result_size += it->size(); + } + + STLStringResizeUninitialized(&result, result_size); // Joins strings - absl::string_view sep("", 0); - for (Iterator it = start; it != end; ++it) { - result.append(sep.data(), sep.size()); - result.append(it->data(), it->size()); - sep = s; + char* result_buf = &*result.begin(); + memcpy(result_buf, start->data(), start->size()); + result_buf += start->size(); + for (Iterator it = start; ++it != end;) { + memcpy(result_buf, s.data(), s.size()); + result_buf += s.size(); + memcpy(result_buf, it->data(), it->size()); + result_buf += it->size(); } } |