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Diffstat (limited to 'absl/strings/internal/str_join_internal.h')
| -rw-r--r-- | absl/strings/internal/str_join_internal.h | 314 |
1 files changed, 314 insertions, 0 deletions
diff --git a/absl/strings/internal/str_join_internal.h b/absl/strings/internal/str_join_internal.h new file mode 100644 index 00000000..e73f1dde --- /dev/null +++ b/absl/strings/internal/str_join_internal.h @@ -0,0 +1,314 @@ +// +// 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 +// +// http://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 <cassert> +#include <iterator> +#include <memory> +#include <string> +#include <utility> + +#include "absl/strings/internal/ostringstream.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 std::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; +} + +// 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 +// 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 std::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 +// 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> +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)); + + // 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; + } + } + + 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_ |