C++: Complex copy-construction & How to prevent copy-construction (thus preventing pass-by-value)

整理自：Thinking in C++

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Complex copy-construction

这里说的 complex，意思是包含 object 的 object。比如：

class T {
	...
};

class V {
private: 
	T t;
	...
};

int main() {
	T t;
	V v(t);
}

那么在 copy v 的时候，t 的 copy 由谁来负责呢？其实不用担心，v 的 copy-constructor 会自动调用 t 的 copy-constructor，形成 copy-constructor 的 chain。

Preventing copy-construction

There’s a simple technique for preventing pass-by-value: declare a private copy-constructor.

class T {
	T(const T&); // Prevent copy-construction
};

No definition is necessary because it never gets called, unless one of your member functions or a friend function needs to perform a pass-by-value.