217 lines
8.1 KiB
C++
217 lines
8.1 KiB
C++
//
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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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// -----------------------------------------------------------------------------
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// File: str_replace.h
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// -----------------------------------------------------------------------------
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//
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// This file defines `absl::StrReplaceAll()`, a general-purpose string
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// replacement function designed for large, arbitrary text substitutions,
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// especially on strings which you are receiving from some other system for
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// further processing (e.g. processing regular expressions, escaping HTML
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// entities, etc.). `StrReplaceAll` is designed to be efficient even when only
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// one substitution is being performed, or when substitution is rare.
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//
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// If the string being modified is known at compile-time, and the substitutions
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// vary, `absl::Substitute()` may be a better choice.
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//
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// Example:
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//
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// std::string html_escaped = absl::StrReplaceAll(user_input, {
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// {"&", "&"},
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// {"<", "<"},
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// {">", ">"},
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// {"\"", """},
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// {"'", "'"}});
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#ifndef ABSL_STRINGS_STR_REPLACE_H_
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#define ABSL_STRINGS_STR_REPLACE_H_
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#include <string>
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#include <utility>
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#include <vector>
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#include "absl/base/attributes.h"
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#include "absl/strings/string_view.h"
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namespace absl {
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// StrReplaceAll()
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//
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// Replaces character sequences within a given string with replacements provided
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// within an initializer list of key/value pairs. Candidate replacements are
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// considered in order as they occur within the string, with earlier matches
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// taking precedence, and longer matches taking precedence for candidates
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// starting at the same position in the string. Once a substitution is made, the
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// replaced text is not considered for any further substitutions.
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//
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// Example:
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//
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// std::string s = absl::StrReplaceAll(
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// "$who bought $count #Noun. Thanks $who!",
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// {{"$count", absl::StrCat(5)},
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// {"$who", "Bob"},
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// {"#Noun", "Apples"}});
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// EXPECT_EQ("Bob bought 5 Apples. Thanks Bob!", s);
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ABSL_MUST_USE_RESULT std::string StrReplaceAll(
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absl::string_view s,
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std::initializer_list<std::pair<absl::string_view, absl::string_view>>
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replacements);
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// Overload of `StrReplaceAll()` to accept a container of key/value replacement
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// pairs (typically either an associative map or a `std::vector` of `std::pair`
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// elements). A vector of pairs is generally more efficient.
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//
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// Examples:
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//
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// std::map<const absl::string_view, const absl::string_view> replacements;
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// replacements["$who"] = "Bob";
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// replacements["$count"] = "5";
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// replacements["#Noun"] = "Apples";
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// std::string s = absl::StrReplaceAll(
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// "$who bought $count #Noun. Thanks $who!",
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// replacements);
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// EXPECT_EQ("Bob bought 5 Apples. Thanks Bob!", s);
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//
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// // A std::vector of std::pair elements can be more efficient.
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// std::vector<std::pair<const absl::string_view, std::string>> replacements;
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// replacements.push_back({"&", "&"});
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// replacements.push_back({"<", "<"});
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// replacements.push_back({">", ">"});
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// std::string s = absl::StrReplaceAll("if (ptr < &foo)",
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// replacements);
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// EXPECT_EQ("if (ptr < &foo)", s);
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template <typename StrToStrMapping>
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std::string StrReplaceAll(absl::string_view s,
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const StrToStrMapping& replacements);
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// Overload of `StrReplaceAll()` to replace character sequences within a given
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// output string *in place* with replacements provided within an initializer
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// list of key/value pairs, returning the number of substitutions that occurred.
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//
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// Example:
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//
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// std::string s = std::string("$who bought $count #Noun. Thanks $who!");
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// int count;
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// count = absl::StrReplaceAll({{"$count", absl::StrCat(5)},
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// {"$who", "Bob"},
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// {"#Noun", "Apples"}}, &s);
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// EXPECT_EQ(count, 4);
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// EXPECT_EQ("Bob bought 5 Apples. Thanks Bob!", s);
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int StrReplaceAll(
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std::initializer_list<std::pair<absl::string_view, absl::string_view>>
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replacements,
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std::string* target);
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// Overload of `StrReplaceAll()` to replace patterns within a given output
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// string *in place* with replacements provided within a container of key/value
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// pairs.
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//
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// Example:
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//
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// std::string s = std::string("if (ptr < &foo)");
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// int count = absl::StrReplaceAll({{"&", "&"},
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// {"<", "<"},
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// {">", ">"}}, &s);
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// EXPECT_EQ(count, 2);
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// EXPECT_EQ("if (ptr < &foo)", s);
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template <typename StrToStrMapping>
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int StrReplaceAll(const StrToStrMapping& replacements, std::string* target);
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// Implementation details only, past this point.
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namespace strings_internal {
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struct ViableSubstitution {
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absl::string_view old;
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absl::string_view replacement;
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size_t offset;
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ViableSubstitution(absl::string_view old_str,
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absl::string_view replacement_str, size_t offset_val)
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: old(old_str), replacement(replacement_str), offset(offset_val) {}
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// One substitution occurs "before" another (takes priority) if either
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// it has the lowest offset, or it has the same offset but a larger size.
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bool OccursBefore(const ViableSubstitution& y) const {
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if (offset != y.offset) return offset < y.offset;
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return old.size() > y.old.size();
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}
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};
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// Build a vector of ViableSubstitutions based on the given list of
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// replacements. subs can be implemented as a priority_queue. However, it turns
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// out that most callers have small enough a list of substitutions that the
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// overhead of such a queue isn't worth it.
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template <typename StrToStrMapping>
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std::vector<ViableSubstitution> FindSubstitutions(
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absl::string_view s, const StrToStrMapping& replacements) {
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std::vector<ViableSubstitution> subs;
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subs.reserve(replacements.size());
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for (const auto& rep : replacements) {
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using std::get;
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absl::string_view old(get<0>(rep));
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size_t pos = s.find(old);
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if (pos == s.npos) continue;
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// Ignore attempts to replace "". This condition is almost never true,
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// but above condition is frequently true. That's why we test for this
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// now and not before.
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if (old.empty()) continue;
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subs.emplace_back(old, get<1>(rep), pos);
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// Insertion sort to ensure the last ViableSubstitution comes before
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// all the others.
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size_t index = subs.size();
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while (--index && subs[index - 1].OccursBefore(subs[index])) {
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std::swap(subs[index], subs[index - 1]);
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}
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}
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return subs;
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}
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int ApplySubstitutions(absl::string_view s,
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std::vector<ViableSubstitution>* subs_ptr,
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std::string* result_ptr);
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} // namespace strings_internal
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template <typename StrToStrMapping>
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std::string StrReplaceAll(absl::string_view s,
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const StrToStrMapping& replacements) {
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auto subs = strings_internal::FindSubstitutions(s, replacements);
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std::string result;
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result.reserve(s.size());
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strings_internal::ApplySubstitutions(s, &subs, &result);
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return result;
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}
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template <typename StrToStrMapping>
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int StrReplaceAll(const StrToStrMapping& replacements, std::string* target) {
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auto subs = strings_internal::FindSubstitutions(*target, replacements);
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if (subs.empty()) return 0;
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std::string result;
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result.reserve(target->size());
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int substitutions =
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strings_internal::ApplySubstitutions(*target, &subs, &result);
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target->swap(result);
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return substitutions;
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}
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} // namespace absl
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#endif // ABSL_STRINGS_STR_REPLACE_H_
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