mirror of
https://github.com/facebook/react-native.git
synced 2025-11-01 09:14:26 +00:00
Samuel Susla
5fa6c5a941
Summary: changelog: [internal] You can read more about this rule on https://clang.llvm.org/extra/clang-tidy/checks/modernize-pass-by-value.html # Isn't it wasteful to copy? Isn't reference more efficient? This rule of thumb is no longer true since C++11 with move semantics. Let's look at some examples. # Option one ``` class TextHolder { public: TextBox(std::string const &text) : text_(text) {} private: std::string text_; }; ``` By using reference here, we prevent the caller from using rvalue to and avoiding copy. Regardless of what the caller passes in, copy always happens. # Option two ``` class TextHolder { public: TextBox(std::string const &text) : text_(text) {} TextBox(std::string &&text) : text_(std::move(text)) {} private: std::string text_; }; ``` Here, we provide two constructors, one for const reference and one for rvalue reference. This gives the caller option to avoid copy. But now we have two constructors, which is not ideal. # Option three (what we do in this diff) ``` class TextHolder { public: TextBox(std::string text) : text_(std::move(text)) {} private: std::string text_; }; ``` Here, the caller has option to avoid copy and we only have single constructor. Reviewed By: fkgozali, JoshuaGross Differential Revision: D33276841 fbshipit-source-id: 619d5123d2e28937b22874650366629f24f20a63
81 lines
2.4 KiB
C++
81 lines
2.4 KiB
C++
/*
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* Copyright (c) Facebook, Inc. and its affiliates.
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*
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* This source code is licensed under the MIT license found in the
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* LICENSE file in the root directory of this source tree.
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*/
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#pragma once
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#include <memory>
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#include <react/renderer/attributedstring/AttributedString.h>
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namespace facebook {
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namespace react {
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/*
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* Represents an object storing a shared `AttributedString` or a shared pointer
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* to some opaque platform-specific object that can be used as an attributed
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* string. The class serves two main purposes:
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* - Represent type-erased attributed string entity (which can be
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* platform-specific or platform-independent);
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* - Represent a container that can be copied with constant complexity.
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*/
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class AttributedStringBox final {
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public:
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enum class Mode { Value, OpaquePointer };
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/*
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* Default constructor constructs an empty string.
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*/
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AttributedStringBox();
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/*
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* Custom explicit constructors.
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*/
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explicit AttributedStringBox(AttributedString const &value);
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explicit AttributedStringBox(std::shared_ptr<void> opaquePointer);
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/*
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* Movable, Copyable, Assignable.
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*/
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AttributedStringBox(AttributedStringBox const &other) = default;
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AttributedStringBox(AttributedStringBox &&other) noexcept;
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AttributedStringBox &operator=(AttributedStringBox const &other) = default;
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AttributedStringBox &operator=(AttributedStringBox &&other);
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/*
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* Getters.
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*/
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Mode getMode() const;
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AttributedString const &getValue() const;
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std::shared_ptr<void> getOpaquePointer() const;
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private:
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Mode mode_;
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std::shared_ptr<AttributedString const> value_;
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std::shared_ptr<void> opaquePointer_;
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};
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bool operator==(AttributedStringBox const &lhs, AttributedStringBox const &rhs);
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bool operator!=(AttributedStringBox const &lhs, AttributedStringBox const &rhs);
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} // namespace react
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} // namespace facebook
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template <>
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struct std::hash<facebook::react::AttributedStringBox> {
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size_t operator()(
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facebook::react::AttributedStringBox const &attributedStringBox) const {
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switch (attributedStringBox.getMode()) {
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case facebook::react::AttributedStringBox::Mode::Value:
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return std::hash<facebook::react::AttributedString>()(
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attributedStringBox.getValue());
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case facebook::react::AttributedStringBox::Mode::OpaquePointer:
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return std::hash<std::shared_ptr<void>>()(
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attributedStringBox.getOpaquePointer());
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}
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}
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};
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