C++核心準(zhǔn)則C.80:如果明確希望使用默認(rèn)語義,使用=default

黃鐵礦晶簇

C.80: Use =default if you have to be explicit about using the default semantics

C.80:如果明確希望使用默認(rèn)語義，使用=default

The compiler is more likely to get the default semantics right and you cannot implement these functions better than the compiler.

編譯器更有可能正確地處理默認(rèn)函數(shù)的語義，你無法比編譯器做得更好。

class Tracer {
 ? ?string message;
public:
 ? ?Tracer(const string& m) : message{m} { cerr << "entering " << message << '\n'; }
 ? ?~Tracer() { cerr << "exiting " << message << '\n'; }

 ? ?Tracer(const Tracer&) = default;
 ? ?Tracer& operator=(const Tracer&) = default;
 ? ?Tracer(Tracer&&) = default;
 ? ?Tracer& operator=(Tracer&&) = default;
};

Because we defined the destructor, we must define the copy and move operations. The = default is the best and simplest way of doing that.

因?yàn)槎x了析構(gòu)函數(shù)，我們必須定義拷貝和移動操作。使用=default是達(dá)到相同效果的最好、最簡單的方式。

class Tracer2 {
 ? ?string message;
public:
 ? ?Tracer2(const string& m) : message{m} { cerr << "entering " << message << '\n'; }
 ? ?~Tracer2() { cerr << "exiting " << message << '\n'; }

 ? ?Tracer2(const Tracer2& a) : message{a.message} {}
 ? ?Tracer2& operator=(const Tracer2& a) { message = a.message; return *this; }
 ? ?Tracer2(Tracer2&& a) :message{a.message} {}
 ? ?Tracer2& operator=(Tracer2&& a) { message = a.message; return *this; }
};

Writing out the bodies of the copy and move operations is verbose, tedious, and error-prone. A compiler does it better.

實(shí)際實(shí)現(xiàn)拷貝和移動操作的工作冗長、乏味且易錯。編譯器會做得更好。

(Moderate) The body of a special operation should not have the same accessibility and semantics as the compiler-generated version, because that would be redundant

(中等)實(shí)現(xiàn)和編譯器生成版本相同的可訪問性和語義的特殊函數(shù)是多余的工作。

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