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2d68b2c593
The `str()` method must be non-const because it may need to internally mutate the representation of the string in order to have an owned `std::string` instance holding the exact string (not a superstring). This is inconvenient in contexts where we can ensure that no mutation is needed to get a `std::string const&`. Add a `str_if_stable() const` method that returns `std::string const*` so we can return `nullptr` if if mutation would be necessary to get a `std::string const&`. Add supporting `is_stable() const` and `stabilize()` methods to check and enforce stable availability of `std::string const&`. These can be used to create `String const` instances from which we can still get a `std::string const&` via `*str_if_stable()` by maintaining the stability invariant at runtime.
153 lines
3.4 KiB
C++
153 lines
3.4 KiB
C++
/* Distributed under the OSI-approved BSD 3-Clause License. See accompanying
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file Copyright.txt or https://cmake.org/licensing for details. */
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#define _SCL_SECURE_NO_WARNINGS
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#include "cmString.hxx"
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#include <memory>
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#include <ostream>
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#include <stdexcept>
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#include <string>
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#include <type_traits>
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namespace cm {
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static std::string const empty_string_;
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void String::internally_mutate_to_stable_string()
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{
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// We assume that only one thread mutates this instance at
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// a time even if we point to a shared string buffer refernced
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// by other threads.
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*this = String(data(), size());
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}
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bool String::is_stable() const
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{
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return str_if_stable() != nullptr;
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}
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void String::stabilize()
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{
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if (is_stable()) {
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return;
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}
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this->internally_mutate_to_stable_string();
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}
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std::string const* String::str_if_stable() const
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{
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if (!data()) {
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// We view no string.
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// This is stable for the lifetime of our current value.
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return &empty_string_;
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}
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if (string_ && data() == string_->data() && size() == string_->size()) {
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// We view an entire string.
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// This is stable for the lifetime of our current value.
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return string_.get();
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}
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return nullptr;
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}
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std::string const& String::str()
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{
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if (std::string const* s = str_if_stable()) {
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return *s;
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}
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// Mutate to hold a std::string that is stable for the lifetime
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// of our current value.
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this->internally_mutate_to_stable_string();
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return *string_;
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}
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const char* String::c_str()
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{
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const char* c = data();
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if (c == nullptr) {
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return c;
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}
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// We always point into a null-terminated string so it is safe to
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// access one past the end. If it is a null byte then we can use
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// the pointer directly.
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if (c[size()] == '\0') {
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return c;
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}
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// Mutate to hold a std::string so we can get a null terminator.
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this->internally_mutate_to_stable_string();
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c = string_->c_str();
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return c;
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}
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String& String::insert(size_type index, size_type count, char ch)
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{
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std::string s;
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s.reserve(size() + count);
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s.assign(data(), size());
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s.insert(index, count, ch);
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return *this = std::move(s);
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}
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String& String::erase(size_type index, size_type count)
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{
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if (index > size()) {
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throw std::out_of_range("Index out of range in String::erase");
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}
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size_type const rcount = std::min(count, size() - index);
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size_type const rindex = index + rcount;
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std::string s;
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s.reserve(size() - rcount);
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s.assign(data(), index);
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s.append(data() + rindex, size() - rindex);
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return *this = std::move(s);
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}
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String String::substr(size_type pos, size_type count) const
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{
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if (pos > size()) {
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throw std::out_of_range("Index out of range in String::substr");
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}
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return String(*this, pos, count);
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}
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String::String(std::string&& s, Private)
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: string_(std::make_shared<std::string>(std::move(s)))
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, view_(string_->data(), string_->size())
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{
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}
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String::size_type String::copy(char* dest, size_type count,
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size_type pos) const
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{
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return view_.copy(dest, count, pos);
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}
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std::ostream& operator<<(std::ostream& os, String const& s)
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{
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return os.write(s.data(), s.size());
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}
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std::string& operator+=(std::string& self, String const& s)
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{
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return self += s.view();
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}
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String IntoString<char*>::into_string(const char* s)
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{
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if (!s) {
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return String();
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}
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return std::string(s);
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}
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string_view AsStringView<String>::view(String const& s)
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{
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return s.view();
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}
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} // namespace cm
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