Usage of C++ function transfer ownership parameters

In C, a function can use a transfer ownership parameter (declared with the && reference character) to transfer ownership of an object from the caller to the callee. This ownership transfer method improves efficiency and avoids unnecessary copy operations. For example, in the StringPool class, the intern() method can receive a string via an rvalue or lvalue argument to be destroyed and transfer ownership of the string to the pool.

Usage of C function transfer ownership parameters

Introduction

In C , the function can receive parameters of different ownership types. The transfer ownership parameter is an efficient and safe mechanism to transfer ownership of an object from the caller to the callee. This article explores how to use the Transfer Ownership parameter and provides a practical example to demonstrate its use.

Function signature

To declare a function that accepts a transfer ownership argument, use the && quoting notation:

void take_ownership(string&& str);

function The formal parameter is a reference and is declared as &&, indicating that the reference is bound to an rvalue or an lvalue that is about to be destroyed.

Semantics

When a function receives a transfer ownership parameter, ownership of the passed object is transferred to the function. The caller no longer owns the object, and the function is responsible for destroying it. This transfer of ownership helps improve efficiency because unnecessary copy operations are avoided.

Practical case

Suppose there is a StringPool class that manages a set of strings. This class has an intern() method that adds a string to the pool. The string should not be copied to the pool, but its ownership should be transferred to the pool.

class StringPool {
public:
    void intern(string&& str) {
        // 将字符串添加到池中
        strings_.emplace_back(move(str));
    }

private:
    vector<string> strings_;
};

In the intern() method, the && reference parameter transfers string ownership to the StringPool. The move() function is used to extract a value from str and transfer it to the internal string vector of StringPool.

Using

To use the transfer-ownership argument, pass an rvalue or an lvalue to be destroyed as the argument. For example:

StringPool pool;
pool.intern("Hello"); // 创建 "Hello" 的唯一所有权副本，并转移到池中

By using the transfer ownership parameter, the intern() method can efficiently add strings to the pool while avoiding unnecessary string copies.

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