--- /dev/null
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+// This file declares INTERNAL parts of the Join API that are inlined/templated
+// or otherwise need to be available at compile time. The main abstractions
+// defined in this file are:
+//
+// - A handful of default Formatters
+// - JoinAlgorithm() overloads
+// - JoinRange() overloads
+// - JoinTuple()
+//
+// DO NOT INCLUDE THIS FILE DIRECTLY. Use this file by including
+// absl/strings/str_join.h
+//
+// IWYU pragma: private, include "absl/strings/str_join.h"
+
+#ifndef ABSL_STRINGS_INTERNAL_STR_JOIN_INTERNAL_H_
+#define ABSL_STRINGS_INTERNAL_STR_JOIN_INTERNAL_H_
+
+#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 {
+namespace strings_internal {
+
+//
+// Formatter objects
+//
+// The following are implementation classes for standard Formatter objects. The
+// factory functions that users will call to create and use these formatters are
+// defined and documented in strings/join.h.
+//
+
+// The default formatter. Converts alpha-numeric types to strings.
+struct AlphaNumFormatterImpl {
+ // This template is needed in order to support passing in a dereferenced
+ // vector<bool>::iterator
+ template <typename T>
+ void operator()(std::string* out, const T& t) const {
+ StrAppend(out, AlphaNum(t));
+ }
+
+ void operator()(std::string* out, const AlphaNum& t) const {
+ StrAppend(out, t);
+ }
+};
+
+// A type that's used to overload the JoinAlgorithm() function (defined below)
+// for ranges that do not require additional formatting (e.g., a range of
+// strings).
+
+struct NoFormatter : public AlphaNumFormatterImpl {};
+
+// Formats types to strings using the << operator.
+class StreamFormatterImpl {
+ public:
+ // The method isn't const because it mutates state. Making it const will
+ // render StreamFormatterImpl thread-hostile.
+ template <typename T>
+ void operator()(std::string* out, const T& t) {
+ // The stream is created lazily to avoid paying the relatively high cost
+ // of its construction when joining an empty range.
+ if (strm_) {
+ strm_->clear(); // clear the bad, fail and eof bits in case they were set
+ strm_->str(out);
+ } else {
+ strm_.reset(new strings_internal::OStringStream(out));
+ }
+ *strm_ << t;
+ }
+
+ private:
+ std::unique_ptr<strings_internal::OStringStream> strm_;
+};
+
+// Formats a std::pair<>. The 'first' member is formatted using f1_ and the
+// 'second' member is formatted using f2_. sep_ is the separator.
+template <typename F1, typename F2>
+class PairFormatterImpl {
+ public:
+ PairFormatterImpl(F1 f1, absl::string_view sep, F2 f2)
+ : f1_(std::move(f1)), sep_(sep), f2_(std::move(f2)) {}
+
+ template <typename T>
+ void operator()(std::string* out, const T& p) {
+ f1_(out, p.first);
+ out->append(sep_);
+ f2_(out, p.second);
+ }
+
+ template <typename T>
+ void operator()(std::string* out, const T& p) const {
+ f1_(out, p.first);
+ out->append(sep_);
+ f2_(out, p.second);
+ }
+
+ private:
+ F1 f1_;
+ std::string sep_;
+ F2 f2_;
+};
+
+// Wraps another formatter and dereferences the argument to operator() then
+// passes the dereferenced argument to the wrapped formatter. This can be
+// useful, for example, to join a std::vector<int*>.
+template <typename Formatter>
+class DereferenceFormatterImpl {
+ public:
+ DereferenceFormatterImpl() : f_() {}
+ explicit DereferenceFormatterImpl(Formatter&& f)
+ : f_(std::forward<Formatter>(f)) {}
+
+ template <typename T>
+ void operator()(std::string* out, const T& t) {
+ f_(out, *t);
+ }
+
+ template <typename T>
+ void operator()(std::string* out, const T& t) const {
+ f_(out, *t);
+ }
+
+ private:
+ Formatter f_;
+};
+
+// DefaultFormatter<T> is a traits class that selects a default Formatter to use
+// for the given type T. The ::Type member names the Formatter to use. This is
+// used by the strings::Join() functions that do NOT take a Formatter argument,
+// in which case a default Formatter must be chosen.
+//
+// AlphaNumFormatterImpl is the default in the base template, followed by
+// specializations for other types.
+template <typename ValueType>
+struct DefaultFormatter {
+ typedef AlphaNumFormatterImpl Type;
+};
+template <>
+struct DefaultFormatter<const char*> {
+ typedef AlphaNumFormatterImpl Type;
+};
+template <>
+struct DefaultFormatter<char*> {
+ typedef AlphaNumFormatterImpl Type;
+};
+template <>
+struct DefaultFormatter<std::string> {
+ typedef NoFormatter Type;
+};
+template <>
+struct DefaultFormatter<absl::string_view> {
+ typedef NoFormatter Type;
+};
+template <typename ValueType>
+struct DefaultFormatter<ValueType*> {
+ typedef DereferenceFormatterImpl<typename DefaultFormatter<ValueType>::Type>
+ Type;
+};
+
+template <typename ValueType>
+struct DefaultFormatter<std::unique_ptr<ValueType>>
+ : public DefaultFormatter<ValueType*> {};
+
+//
+// JoinAlgorithm() functions
+//
+
+// The main joining algorithm. This simply joins the elements in the given
+// iterator range, each separated by the given separator, into an output string,
+// and formats each element using the provided Formatter object.
+template <typename Iterator, typename Formatter>
+std::string JoinAlgorithm(Iterator start, Iterator end, absl::string_view s,
+ Formatter&& f) {
+ std::string result;
+ absl::string_view sep("");
+ for (Iterator it = start; it != end; ++it) {
+ result.append(sep.data(), sep.size());
+ f(&result, *it);
+ sep = s;
+ }
+ return result;
+}
+
+// A joining algorithm that's optimized for a forward iterator range of
+// string-like objects that do not need any additional formatting. This is to
+// optimize the common case of joining, say, a std::vector<string> or a
+// std::vector<absl::string_view>.
+//
+// This is an overload of the previous JoinAlgorithm() function. Here the
+// Formatter argument is of type NoFormatter. Since NoFormatter is an internal
+// type, this overload is only invoked when strings::Join() is called with a
+// range of string-like objects (e.g., std::string, absl::string_view), and an
+// explicit Formatter argument was NOT specified.
+//
+// The optimization is that the needed space will be reserved in the output
+// 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 string.
+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) {
+ // Sums size
+ size_t result_size = start->size();
+ for (Iterator it = start; ++it != end;) {
+ result_size += s.size();
+ result_size += it->size();
+ }
+
+ if (result_size > 0) {
+ STLStringResizeUninitialized(&result, result_size);
+
+ // Joins strings
+ 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();
+ }
+ }
+ }
+
+ return result;
+}
+
+// JoinTupleLoop implements a loop over the elements of a std::tuple, which
+// are heterogeneous. The primary template matches the tuple interior case. It
+// continues the iteration after appending a separator (for nonzero indices)
+// and formatting an element of the tuple. The specialization for the I=N case
+// matches the end-of-tuple, and terminates the iteration.
+template <size_t I, size_t N>
+struct JoinTupleLoop {
+ template <typename Tup, typename Formatter>
+ void operator()(std::string* out, const Tup& tup, absl::string_view sep,
+ Formatter&& fmt) {
+ if (I > 0) out->append(sep.data(), sep.size());
+ fmt(out, std::get<I>(tup));
+ JoinTupleLoop<I + 1, N>()(out, tup, sep, fmt);
+ }
+};
+template <size_t N>
+struct JoinTupleLoop<N, N> {
+ template <typename Tup, typename Formatter>
+ void operator()(std::string*, const Tup&, absl::string_view, Formatter&&) {}
+};
+
+template <typename... T, typename Formatter>
+std::string JoinAlgorithm(const std::tuple<T...>& tup, absl::string_view sep,
+ Formatter&& fmt) {
+ std::string result;
+ JoinTupleLoop<0, sizeof...(T)>()(&result, tup, sep, fmt);
+ return result;
+}
+
+template <typename Iterator>
+std::string JoinRange(Iterator first, Iterator last,
+ absl::string_view separator) {
+ // No formatter was explicitly given, so a default must be chosen.
+ typedef typename std::iterator_traits<Iterator>::value_type ValueType;
+ typedef typename DefaultFormatter<ValueType>::Type Formatter;
+ return JoinAlgorithm(first, last, separator, Formatter());
+}
+
+template <typename Range, typename Formatter>
+std::string JoinRange(const Range& range, absl::string_view separator,
+ Formatter&& fmt) {
+ using std::begin;
+ using std::end;
+ return JoinAlgorithm(begin(range), end(range), separator, fmt);
+}
+
+template <typename Range>
+std::string JoinRange(const Range& range, absl::string_view separator) {
+ using std::begin;
+ using std::end;
+ return JoinRange(begin(range), end(range), separator);
+}
+
+} // namespace strings_internal
+} // namespace absl
+
+#endif // ABSL_STRINGS_INTERNAL_STR_JOIN_INTERNAL_H_
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