C++: typedef & alias declaration (using)

整理自 C++ Primer, 5th Edition

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所谓 alias declaration 就是 using X = Y;，它和 typedef Y X; 是完全等价的：

class SalesItem {

};

class SalesReport {
	
};

int main() {
	typedef SalesItem SI, *PSI;
	// equivalent to:
	// typedef SalesItem SI;
	// typedef SalesItem* PSI;
	
	using SR = SalesReport;
	using PSR = SalesReport*;
	
	SI si;
	PSI psi = new SI;
	PSI psi2 = new SalesItem;
	
	SR sr;
	PSR psr = new SR;
	PSR psr2 = new SalesReport;
	
	delete psi;
	delete psi2;
	delete psr;
	delete psr2;
}

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~~~~~~~~~~ 2015-05-16 补充；来自 C++ Primer, 5th Edition ~~~~~~~~~~

Under C++11, we are able to define a type alias for a class template:

template<typename T> using twin = pair<T, T>;
twin<string> authors; // authors is a pair<string, string>

template <typename T> using partNo = pair<T, unsigned>;
partNo<string> books; // books is a pair<string, unsigned>

简单地说就是 twin<T> == pair<T, T> 和 partNo<T> == pair<T, unsigned>。注意这种语法。