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TMessagesProj/jni/voip/webrtc/absl/strings/string_view.h

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+//
+// 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.
+//
+// -----------------------------------------------------------------------------
+// File: string_view.h
+// -----------------------------------------------------------------------------
+//
+// This file contains the definition of the `absl::string_view` class. A
+// `string_view` points to a contiguous span of characters, often part or all of
+// another `std::string`, double-quoted string literal, character array, or even
+// another `string_view`.
+//
+// This `absl::string_view` abstraction is designed to be a drop-in
+// replacement for the C++17 `std::string_view` abstraction.
+#ifndef ABSL_STRINGS_STRING_VIEW_H_
+#define ABSL_STRINGS_STRING_VIEW_H_
+
+#include <algorithm>
+#include <cassert>
+#include <cstddef>
+#include <cstring>
+#include <iosfwd>
+#include <iterator>
+#include <limits>
+#include <string>
+
+#include "absl/base/attributes.h"
+#include "absl/base/nullability.h"
+#include "absl/base/config.h"
+#include "absl/base/internal/throw_delegate.h"
+#include "absl/base/macros.h"
+#include "absl/base/optimization.h"
+#include "absl/base/port.h"
+
+#ifdef ABSL_USES_STD_STRING_VIEW
+
+#include <string_view>  // IWYU pragma: export
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+using string_view = std::string_view;
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#else  // ABSL_USES_STD_STRING_VIEW
+
+#if ABSL_HAVE_BUILTIN(__builtin_memcmp) ||        \
+    (defined(__GNUC__) && !defined(__clang__)) || \
+    (defined(_MSC_VER) && _MSC_VER >= 1928)
+#define ABSL_INTERNAL_STRING_VIEW_MEMCMP __builtin_memcmp
+#else  // ABSL_HAVE_BUILTIN(__builtin_memcmp)
+#define ABSL_INTERNAL_STRING_VIEW_MEMCMP memcmp
+#endif  // ABSL_HAVE_BUILTIN(__builtin_memcmp)
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+// absl::string_view
+//
+// A `string_view` provides a lightweight view into the string data provided by
+// a `std::string`, double-quoted string literal, character array, or even
+// another `string_view`. A `string_view` does *not* own the string to which it
+// points, and that data cannot be modified through the view.
+//
+// You can use `string_view` as a function or method parameter anywhere a
+// parameter can receive a double-quoted string literal, `const char*`,
+// `std::string`, or another `absl::string_view` argument with no need to copy
+// the string data. Systematic use of `string_view` within function arguments
+// reduces data copies and `strlen()` calls.
+//
+// Because of its small size, prefer passing `string_view` by value:
+//
+//   void MyFunction(absl::string_view arg);
+//
+// If circumstances require, you may also pass one by const reference:
+//
+//   void MyFunction(const absl::string_view& arg);  // not preferred
+//
+// Passing by value generates slightly smaller code for many architectures.
+//
+// In either case, the source data of the `string_view` must outlive the
+// `string_view` itself.
+//
+// A `string_view` is also suitable for local variables if you know that the
+// lifetime of the underlying object is longer than the lifetime of your
+// `string_view` variable. However, beware of binding a `string_view` to a
+// temporary value:
+//
+//   // BAD use of string_view: lifetime problem
+//   absl::string_view sv = obj.ReturnAString();
+//
+//   // GOOD use of string_view: str outlives sv
+//   std::string str = obj.ReturnAString();
+//   absl::string_view sv = str;
+//
+// Due to lifetime issues, a `string_view` is sometimes a poor choice for a
+// return value and usually a poor choice for a data member. If you do use a
+// `string_view` this way, it is your responsibility to ensure that the object
+// pointed to by the `string_view` outlives the `string_view`.
+//
+// A `string_view` may represent a whole string or just part of a string. For
+// example, when splitting a string, `std::vector<absl::string_view>` is a
+// natural data type for the output.
+//
+// For another example, a Cord is a non-contiguous, potentially very
+// long string-like object.  The Cord class has an interface that iteratively
+// provides string_view objects that point to the successive pieces of a Cord
+// object.
+//
+// When constructed from a source which is NUL-terminated, the `string_view`
+// itself will not include the NUL-terminator unless a specific size (including
+// the NUL) is passed to the constructor. As a result, common idioms that work
+// on NUL-terminated strings do not work on `string_view` objects. If you write
+// code that scans a `string_view`, you must check its length rather than test
+// for nul, for example. Note, however, that nuls may still be embedded within
+// a `string_view` explicitly.
+//
+// You may create a null `string_view` in two ways:
+//
+//   absl::string_view sv;
+//   absl::string_view sv(nullptr, 0);
+//
+// For the above, `sv.data() == nullptr`, `sv.length() == 0`, and
+// `sv.empty() == true`. Also, if you create a `string_view` with a non-null
+// pointer then `sv.data() != nullptr`. Thus, you can use `string_view()` to
+// signal an undefined value that is different from other `string_view` values
+// in a similar fashion to how `const char* p1 = nullptr;` is different from
+// `const char* p2 = "";`. However, in practice, it is not recommended to rely
+// on this behavior.
+//
+// Be careful not to confuse a null `string_view` with an empty one. A null
+// `string_view` is an empty `string_view`, but some empty `string_view`s are
+// not null. Prefer checking for emptiness over checking for null.
+//
+// There are many ways to create an empty string_view:
+//
+//   const char* nullcp = nullptr;
+//   // string_view.size() will return 0 in all cases.
+//   absl::string_view();
+//   absl::string_view(nullcp, 0);
+//   absl::string_view("");
+//   absl::string_view("", 0);
+//   absl::string_view("abcdef", 0);
+//   absl::string_view("abcdef" + 6, 0);
+//
+// All empty `string_view` objects whether null or not, are equal:
+//
+//   absl::string_view() == absl::string_view("", 0)
+//   absl::string_view(nullptr, 0) == absl::string_view("abcdef"+6, 0)
+class ABSL_ATTRIBUTE_VIEW string_view {
+ public:
+  using traits_type = std::char_traits<char>;
+  using value_type = char;
+  using pointer = absl::Nullable<char*>;
+  using const_pointer = absl::Nullable<const char*>;
+  using reference = char&;
+  using const_reference = const char&;
+  using const_iterator = absl::Nullable<const char*>;
+  using iterator = const_iterator;
+  using const_reverse_iterator = std::reverse_iterator<const_iterator>;
+  using reverse_iterator = const_reverse_iterator;
+  using size_type = size_t;
+  using difference_type = std::ptrdiff_t;
+  using absl_internal_is_view = std::true_type;
+
+  static constexpr size_type npos = static_cast<size_type>(-1);
+
+  // Null `string_view` constructor
+  constexpr string_view() noexcept : ptr_(nullptr), length_(0) {}
+
+  // Implicit constructors
+
+  template <typename Allocator>
+  string_view(  // NOLINT(runtime/explicit)
+      const std::basic_string<char, std::char_traits<char>, Allocator>& str
+          ABSL_ATTRIBUTE_LIFETIME_BOUND) noexcept
+      // This is implemented in terms of `string_view(p, n)` so `str.size()`
+      // doesn't need to be reevaluated after `ptr_` is set.
+      // The length check is also skipped since it is unnecessary and causes
+      // code bloat.
+      : string_view(str.data(), str.size(), SkipCheckLengthTag{}) {}
+
+  // Implicit constructor of a `string_view` from NUL-terminated `str`. When
+  // accepting possibly null strings, use `absl::NullSafeStringView(str)`
+  // instead (see below).
+  // The length check is skipped since it is unnecessary and causes code bloat.
+  constexpr string_view(  // NOLINT(runtime/explicit)
+      absl::Nonnull<const char*> str)
+      : ptr_(str), length_(str ? StrlenInternal(str) : 0) {}
+
+  // Constructor of a `string_view` from a `const char*` and length.
+  constexpr string_view(absl::Nullable<const char*> data, size_type len)
+      : ptr_(data), length_(CheckLengthInternal(len)) {}
+
+  constexpr string_view(const string_view&) noexcept = default;
+  string_view& operator=(const string_view&) noexcept = default;
+
+  // Iterators
+
+  // string_view::begin()
+  //
+  // Returns an iterator pointing to the first character at the beginning of the
+  // `string_view`, or `end()` if the `string_view` is empty.
+  constexpr const_iterator begin() const noexcept { return ptr_; }
+
+  // string_view::end()
+  //
+  // Returns an iterator pointing just beyond the last character at the end of
+  // the `string_view`. This iterator acts as a placeholder; attempting to
+  // access it results in undefined behavior.
+  constexpr const_iterator end() const noexcept { return ptr_ + length_; }
+
+  // string_view::cbegin()
+  //
+  // Returns a const iterator pointing to the first character at the beginning
+  // of the `string_view`, or `end()` if the `string_view` is empty.
+  constexpr const_iterator cbegin() const noexcept { return begin(); }
+
+  // string_view::cend()
+  //
+  // Returns a const iterator pointing just beyond the last character at the end
+  // of the `string_view`. This pointer acts as a placeholder; attempting to
+  // access its element results in undefined behavior.
+  constexpr const_iterator cend() const noexcept { return end(); }
+
+  // string_view::rbegin()
+  //
+  // Returns a reverse iterator pointing to the last character at the end of the
+  // `string_view`, or `rend()` if the `string_view` is empty.
+  const_reverse_iterator rbegin() const noexcept {
+    return const_reverse_iterator(end());
+  }
+
+  // string_view::rend()
+  //
+  // Returns a reverse iterator pointing just before the first character at the
+  // beginning of the `string_view`. This pointer acts as a placeholder;
+  // attempting to access its element results in undefined behavior.
+  const_reverse_iterator rend() const noexcept {
+    return const_reverse_iterator(begin());
+  }
+
+  // string_view::crbegin()
+  //
+  // Returns a const reverse iterator pointing to the last character at the end
+  // of the `string_view`, or `crend()` if the `string_view` is empty.
+  const_reverse_iterator crbegin() const noexcept { return rbegin(); }
+
+  // string_view::crend()
+  //
+  // Returns a const reverse iterator pointing just before the first character
+  // at the beginning of the `string_view`. This pointer acts as a placeholder;
+  // attempting to access its element results in undefined behavior.
+  const_reverse_iterator crend() const noexcept { return rend(); }
+
+  // Capacity Utilities
+
+  // string_view::size()
+  //
+  // Returns the number of characters in the `string_view`.
+  constexpr size_type size() const noexcept { return length_; }
+
+  // string_view::length()
+  //
+  // Returns the number of characters in the `string_view`. Alias for `size()`.
+  constexpr size_type length() const noexcept { return size(); }
+
+  // string_view::max_size()
+  //
+  // Returns the maximum number of characters the `string_view` can hold.
+  constexpr size_type max_size() const noexcept { return kMaxSize; }
+
+  // string_view::empty()
+  //
+  // Checks if the `string_view` is empty (refers to no characters).
+  constexpr bool empty() const noexcept { return length_ == 0; }
+
+  // string_view::operator[]
+  //
+  // Returns the ith element of the `string_view` using the array operator.
+  // Note that this operator does not perform any bounds checking.
+  constexpr const_reference operator[](size_type i) const {
+    ABSL_HARDENING_ASSERT(i < size());
+    return ptr_[i];
+  }
+
+  // string_view::at()
+  //
+  // Returns the ith element of the `string_view`. Bounds checking is performed,
+  // and an exception of type `std::out_of_range` will be thrown on invalid
+  // access.
+  constexpr const_reference at(size_type i) const {
+    if (ABSL_PREDICT_FALSE(i >= size())) {
+      base_internal::ThrowStdOutOfRange("absl::string_view::at");
+    }
+    return ptr_[i];
+  }
+
+  // string_view::front()
+  //
+  // Returns the first element of a `string_view`.
+  constexpr const_reference front() const {
+    ABSL_HARDENING_ASSERT(!empty());
+    return ptr_[0];
+  }
+
+  // string_view::back()
+  //
+  // Returns the last element of a `string_view`.
+  constexpr const_reference back() const {
+    ABSL_HARDENING_ASSERT(!empty());
+    return ptr_[size() - 1];
+  }
+
+  // string_view::data()
+  //
+  // Returns a pointer to the underlying character array (which is of course
+  // stored elsewhere). Note that `string_view::data()` may contain embedded nul
+  // characters, but the returned buffer may or may not be NUL-terminated;
+  // therefore, do not pass `data()` to a routine that expects a NUL-terminated
+  // string.
+  constexpr const_pointer data() const noexcept { return ptr_; }
+
+  // Modifiers
+
+  // string_view::remove_prefix()
+  //
+  // Removes the first `n` characters from the `string_view`. Note that the
+  // underlying string is not changed, only the view.
+  constexpr void remove_prefix(size_type n) {
+    ABSL_HARDENING_ASSERT(n <= length_);
+    ptr_ += n;
+    length_ -= n;
+  }
+
+  // string_view::remove_suffix()
+  //
+  // Removes the last `n` characters from the `string_view`. Note that the
+  // underlying string is not changed, only the view.
+  constexpr void remove_suffix(size_type n) {
+    ABSL_HARDENING_ASSERT(n <= length_);
+    length_ -= n;
+  }
+
+  // string_view::swap()
+  //
+  // Swaps this `string_view` with another `string_view`.
+  constexpr void swap(string_view& s) noexcept {
+    auto t = *this;
+    *this = s;
+    s = t;
+  }
+
+  // Explicit conversion operators
+
+  // Converts to `std::basic_string`.
+  template <typename A>
+  explicit operator std::basic_string<char, traits_type, A>() const {
+    if (!data()) return {};
+    return std::basic_string<char, traits_type, A>(data(), size());
+  }
+
+  // string_view::copy()
+  //
+  // Copies the contents of the `string_view` at offset `pos` and length `n`
+  // into `buf`.
+  size_type copy(char* buf, size_type n, size_type pos = 0) const {
+    if (ABSL_PREDICT_FALSE(pos > length_)) {
+      base_internal::ThrowStdOutOfRange("absl::string_view::copy");
+    }
+    size_type rlen = (std::min)(length_ - pos, n);
+    if (rlen > 0) {
+      const char* start = ptr_ + pos;
+      traits_type::copy(buf, start, rlen);
+    }
+    return rlen;
+  }
+
+  // string_view::substr()
+  //
+  // Returns a "substring" of the `string_view` (at offset `pos` and length
+  // `n`) as another string_view. This function throws `std::out_of_bounds` if
+  // `pos > size`.
+  // Use absl::ClippedSubstr if you need a truncating substr operation.
+  constexpr string_view substr(size_type pos = 0, size_type n = npos) const {
+    if (ABSL_PREDICT_FALSE(pos > length_)) {
+      base_internal::ThrowStdOutOfRange("absl::string_view::substr");
+    }
+    return string_view(ptr_ + pos, Min(n, length_ - pos));
+  }
+
+  // string_view::compare()
+  //
+  // Performs a lexicographical comparison between this `string_view` and
+  // another `string_view` `x`, returning a negative value if `*this` is less
+  // than `x`, 0 if `*this` is equal to `x`, and a positive value if `*this`
+  // is greater than `x`.
+  constexpr int compare(string_view x) const noexcept {
+    return CompareImpl(length_, x.length_,
+                       Min(length_, x.length_) == 0
+                           ? 0
+                           : ABSL_INTERNAL_STRING_VIEW_MEMCMP(
+                                 ptr_, x.ptr_, Min(length_, x.length_)));
+  }
+
+  // Overload of `string_view::compare()` for comparing a substring of the
+  // 'string_view` and another `absl::string_view`.
+  constexpr int compare(size_type pos1, size_type count1, string_view v) const {
+    return substr(pos1, count1).compare(v);
+  }
+
+  // Overload of `string_view::compare()` for comparing a substring of the
+  // `string_view` and a substring of another `absl::string_view`.
+  constexpr int compare(size_type pos1, size_type count1, string_view v,
+                        size_type pos2, size_type count2) const {
+    return substr(pos1, count1).compare(v.substr(pos2, count2));
+  }
+
+  // Overload of `string_view::compare()` for comparing a `string_view` and a
+  // a different C-style string `s`.
+  constexpr int compare(absl::Nonnull<const char*> s) const {
+    return compare(string_view(s));
+  }
+
+  // Overload of `string_view::compare()` for comparing a substring of the
+  // `string_view` and a different string C-style string `s`.
+  constexpr int compare(size_type pos1, size_type count1,
+                        absl::Nonnull<const char*> s) const {
+    return substr(pos1, count1).compare(string_view(s));
+  }
+
+  // Overload of `string_view::compare()` for comparing a substring of the
+  // `string_view` and a substring of a different C-style string `s`.
+  constexpr int compare(size_type pos1, size_type count1,
+                        absl::Nonnull<const char*> s, size_type count2) const {
+    return substr(pos1, count1).compare(string_view(s, count2));
+  }
+
+  // Find Utilities
+
+  // string_view::find()
+  //
+  // Finds the first occurrence of the substring `s` within the `string_view`,
+  // returning the position of the first character's match, or `npos` if no
+  // match was found.
+  size_type find(string_view s, size_type pos = 0) const noexcept;
+
+  // Overload of `string_view::find()` for finding the given character `c`
+  // within the `string_view`.
+  size_type find(char c, size_type pos = 0) const noexcept;
+
+  // Overload of `string_view::find()` for finding a substring of a different
+  // C-style string `s` within the `string_view`.
+  size_type find(absl::Nonnull<const char*> s, size_type pos,
+                 size_type count) const {
+    return find(string_view(s, count), pos);
+  }
+
+  // Overload of `string_view::find()` for finding a different C-style string
+  // `s` within the `string_view`.
+  size_type find(absl::Nonnull<const char *> s, size_type pos = 0) const {
+    return find(string_view(s), pos);
+  }
+
+  // string_view::rfind()
+  //
+  // Finds the last occurrence of a substring `s` within the `string_view`,
+  // returning the position of the first character's match, or `npos` if no
+  // match was found.
+  size_type rfind(string_view s, size_type pos = npos) const noexcept;
+
+  // Overload of `string_view::rfind()` for finding the last given character `c`
+  // within the `string_view`.
+  size_type rfind(char c, size_type pos = npos) const noexcept;
+
+  // Overload of `string_view::rfind()` for finding a substring of a different
+  // C-style string `s` within the `string_view`.
+  size_type rfind(absl::Nonnull<const char*> s, size_type pos,
+                  size_type count) const {
+    return rfind(string_view(s, count), pos);
+  }
+
+  // Overload of `string_view::rfind()` for finding a different C-style string
+  // `s` within the `string_view`.
+  size_type rfind(absl::Nonnull<const char*> s, size_type pos = npos) const {
+    return rfind(string_view(s), pos);
+  }
+
+  // string_view::find_first_of()
+  //
+  // Finds the first occurrence of any of the characters in `s` within the
+  // `string_view`, returning the start position of the match, or `npos` if no
+  // match was found.
+  size_type find_first_of(string_view s, size_type pos = 0) const noexcept;
+
+  // Overload of `string_view::find_first_of()` for finding a character `c`
+  // within the `string_view`.
+  size_type find_first_of(char c, size_type pos = 0) const noexcept {
+    return find(c, pos);
+  }
+
+  // Overload of `string_view::find_first_of()` for finding a substring of a
+  // different C-style string `s` within the `string_view`.
+  size_type find_first_of(absl::Nonnull<const char*> s, size_type pos,
+                          size_type count) const {
+    return find_first_of(string_view(s, count), pos);
+  }
+
+  // Overload of `string_view::find_first_of()` for finding a different C-style
+  // string `s` within the `string_view`.
+  size_type find_first_of(absl::Nonnull<const char*> s,
+                          size_type pos = 0) const {
+    return find_first_of(string_view(s), pos);
+  }
+
+  // string_view::find_last_of()
+  //
+  // Finds the last occurrence of any of the characters in `s` within the
+  // `string_view`, returning the start position of the match, or `npos` if no
+  // match was found.
+  size_type find_last_of(string_view s, size_type pos = npos) const noexcept;
+
+  // Overload of `string_view::find_last_of()` for finding a character `c`
+  // within the `string_view`.
+  size_type find_last_of(char c, size_type pos = npos) const noexcept {
+    return rfind(c, pos);
+  }
+
+  // Overload of `string_view::find_last_of()` for finding a substring of a
+  // different C-style string `s` within the `string_view`.
+  size_type find_last_of(absl::Nonnull<const char*> s, size_type pos,
+                         size_type count) const {
+    return find_last_of(string_view(s, count), pos);
+  }
+
+  // Overload of `string_view::find_last_of()` for finding a different C-style
+  // string `s` within the `string_view`.
+  size_type find_last_of(absl::Nonnull<const char*> s,
+                         size_type pos = npos) const {
+    return find_last_of(string_view(s), pos);
+  }
+
+  // string_view::find_first_not_of()
+  //
+  // Finds the first occurrence of any of the characters not in `s` within the
+  // `string_view`, returning the start position of the first non-match, or
+  // `npos` if no non-match was found.
+  size_type find_first_not_of(string_view s, size_type pos = 0) const noexcept;
+
+  // Overload of `string_view::find_first_not_of()` for finding a character
+  // that is not `c` within the `string_view`.
+  size_type find_first_not_of(char c, size_type pos = 0) const noexcept;
+
+  // Overload of `string_view::find_first_not_of()` for finding a substring of a
+  // different C-style string `s` within the `string_view`.
+  size_type find_first_not_of(absl::Nonnull<const char*> s, size_type pos,
+                              size_type count) const {
+    return find_first_not_of(string_view(s, count), pos);
+  }
+
+  // Overload of `string_view::find_first_not_of()` for finding a different
+  // C-style string `s` within the `string_view`.
+  size_type find_first_not_of(absl::Nonnull<const char*> s,
+                              size_type pos = 0) const {
+    return find_first_not_of(string_view(s), pos);
+  }
+
+  // string_view::find_last_not_of()
+  //
+  // Finds the last occurrence of any of the characters not in `s` within the
+  // `string_view`, returning the start position of the last non-match, or
+  // `npos` if no non-match was found.
+  size_type find_last_not_of(string_view s,
+                             size_type pos = npos) const noexcept;
+
+  // Overload of `string_view::find_last_not_of()` for finding a character
+  // that is not `c` within the `string_view`.
+  size_type find_last_not_of(char c, size_type pos = npos) const noexcept;
+
+  // Overload of `string_view::find_last_not_of()` for finding a substring of a
+  // different C-style string `s` within the `string_view`.
+  size_type find_last_not_of(absl::Nonnull<const char*> s, size_type pos,
+                             size_type count) const {
+    return find_last_not_of(string_view(s, count), pos);
+  }
+
+  // Overload of `string_view::find_last_not_of()` for finding a different
+  // C-style string `s` within the `string_view`.
+  size_type find_last_not_of(absl::Nonnull<const char*> s,
+                             size_type pos = npos) const {
+    return find_last_not_of(string_view(s), pos);
+  }
+
+#if ABSL_INTERNAL_CPLUSPLUS_LANG >= 202002L
+  // string_view::starts_with()
+  //
+  // Returns true if the `string_view` starts with the prefix `s`.
+  //
+  // This method only exists when targeting at least C++20.
+  // If support for C++ prior to C++20 is required, use `absl::StartsWith()`
+  // from `//absl/strings/match.h` for compatibility.
+  constexpr bool starts_with(string_view s) const noexcept {
+    return s.empty() ||
+           (size() >= s.size() &&
+            ABSL_INTERNAL_STRING_VIEW_MEMCMP(data(), s.data(), s.size()) == 0);
+  }
+
+  // Overload of `string_view::starts_with()` that returns true if `c` is the
+  // first character of the `string_view`.
+  constexpr bool starts_with(char c) const noexcept {
+    return !empty() && front() == c;
+  }
+
+  // Overload of `string_view::starts_with()` that returns true if the
+  // `string_view` starts with the C-style prefix `s`.
+  constexpr bool starts_with(const char* s) const {
+    return starts_with(string_view(s));
+  }
+
+  // string_view::ends_with()
+  //
+  // Returns true if the `string_view` ends with the suffix `s`.
+  //
+  // This method only exists when targeting at least C++20.
+  // If support for C++ prior to C++20 is required, use `absl::EndsWith()`
+  // from `//absl/strings/match.h` for compatibility.
+  constexpr bool ends_with(string_view s) const noexcept {
+    return s.empty() || (size() >= s.size() && ABSL_INTERNAL_STRING_VIEW_MEMCMP(
+                                                   data() + (size() - s.size()),
+                                                   s.data(), s.size()) == 0);
+  }
+
+  // Overload of `string_view::ends_with()` that returns true if `c` is the
+  // last character of the `string_view`.
+  constexpr bool ends_with(char c) const noexcept {
+    return !empty() && back() == c;
+  }
+
+  // Overload of `string_view::ends_with()` that returns true if the
+  // `string_view` ends with the C-style suffix `s`.
+  constexpr bool ends_with(const char* s) const {
+    return ends_with(string_view(s));
+  }
+#endif  // ABSL_INTERNAL_CPLUSPLUS_LANG >= 202002L
+
+ private:
+  // The constructor from std::string delegates to this constructor.
+  // See the comment on that constructor for the rationale.
+  struct SkipCheckLengthTag {};
+  string_view(absl::Nullable<const char*> data, size_type len,
+              SkipCheckLengthTag) noexcept
+      : ptr_(data), length_(len) {}
+
+  static constexpr size_type kMaxSize =
+      (std::numeric_limits<difference_type>::max)();
+
+  static constexpr size_type CheckLengthInternal(size_type len) {
+    ABSL_HARDENING_ASSERT(len <= kMaxSize);
+    return len;
+  }
+
+  static constexpr size_type StrlenInternal(absl::Nonnull<const char*> str) {
+#if defined(_MSC_VER) && !defined(__clang__)
+    // MSVC 2017+ can evaluate this at compile-time.
+    const char* begin = str;
+    while (*str != '\0') ++str;
+    return str - begin;
+#elif ABSL_HAVE_BUILTIN(__builtin_strlen) || \
+    (defined(__GNUC__) && !defined(__clang__))
+    // GCC has __builtin_strlen according to
+    // https://gcc.gnu.org/onlinedocs/gcc-4.7.0/gcc/Other-Builtins.html, but
+    // ABSL_HAVE_BUILTIN doesn't detect that, so we use the extra checks above.
+    // __builtin_strlen is constexpr.
+    return __builtin_strlen(str);
+#else
+    return str ? strlen(str) : 0;
+#endif
+  }
+
+  static constexpr size_t Min(size_type length_a, size_type length_b) {
+    return length_a < length_b ? length_a : length_b;
+  }
+
+  static constexpr int CompareImpl(size_type length_a, size_type length_b,
+                                   int compare_result) {
+    return compare_result == 0 ? static_cast<int>(length_a > length_b) -
+                                     static_cast<int>(length_a < length_b)
+                               : (compare_result < 0 ? -1 : 1);
+  }
+
+  absl::Nullable<const char*> ptr_;
+  size_type length_;
+};
+
+// This large function is defined inline so that in a fairly common case where
+// one of the arguments is a literal, the compiler can elide a lot of the
+// following comparisons.
+constexpr bool operator==(string_view x, string_view y) noexcept {
+  return x.size() == y.size() &&
+         (x.empty() ||
+          ABSL_INTERNAL_STRING_VIEW_MEMCMP(x.data(), y.data(), x.size()) == 0);
+}
+
+constexpr bool operator!=(string_view x, string_view y) noexcept {
+  return !(x == y);
+}
+
+constexpr bool operator<(string_view x, string_view y) noexcept {
+  return x.compare(y) < 0;
+}
+
+constexpr bool operator>(string_view x, string_view y) noexcept {
+  return y < x;
+}
+
+constexpr bool operator<=(string_view x, string_view y) noexcept {
+  return !(y < x);
+}
+
+constexpr bool operator>=(string_view x, string_view y) noexcept {
+  return !(x < y);
+}
+
+// IO Insertion Operator
+std::ostream& operator<<(std::ostream& o, string_view piece);
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#undef ABSL_INTERNAL_STRING_VIEW_MEMCMP
+
+#endif  // ABSL_USES_STD_STRING_VIEW
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+// ClippedSubstr()
+//
+// Like `s.substr(pos, n)`, but clips `pos` to an upper bound of `s.size()`.
+// Provided because std::string_view::substr throws if `pos > size()`
+inline string_view ClippedSubstr(string_view s, size_t pos,
+                                 size_t n = string_view::npos) {
+  pos = (std::min)(pos, static_cast<size_t>(s.size()));
+  return s.substr(pos, n);
+}
+
+// NullSafeStringView()
+//
+// Creates an `absl::string_view` from a pointer `p` even if it's null-valued.
+// This function should be used where an `absl::string_view` can be created from
+// a possibly-null pointer.
+constexpr string_view NullSafeStringView(absl::Nullable<const char*> p) {
+  return p ? string_view(p) : string_view();
+}
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_STRING_VIEW_H_