//
// 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_
