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