//############################################################################
/* Named Parameter Idiom */
/* 主要解决的问题
C++函数只支持位置参数，不支持像Python那样的命名参数
*/
class OpenFile {
public:
OpenFile(string filename, bool readonly=true, bool appendWhenWriting=false,
int blockSize=256, bool unbuffered=true, bool exclusiveAccess=false);
}
//像下面的函数调用，我得记得每个参数的意思和位置，非常不方便，可读性差，而且不灵活
OpenFile pf = OpenFile("foo.txt", true, false, 1024, true, true);
// 理想的情况是像下面这样的:
OpenFile pf = OpenFile(.filename("foo.txt"), .blockSize(1024) );
/* 解决方法 1 */
class OpenFile {
public:
OpenFile(std::string const& filename);
OpenFile& readonly(bool ro) { readonly_ = ro; return *this; }
OpenFile& createIfNotExist(bool c) { createIfNotExist_ = c; return *this; }
OpenFile& blockSize(unsigned nbytes) { blockSize_ = nbytes; return *this; }
...
};
OpenFile f = OpenFile("foo.txt")
.blockSize(1024)
.createIfNotExist(true)
.appendWhenWriting(true)
.unbuffered(false)
.readonly(true)
.exclusiveAccess(false);
OpenFile f = OpenFile("foo.txt").blockSize(1024);
/* 问题:
* 如果是非成员函数呢?
*/
/* 方法 2: 使用类型*/
void setBirthDate(int month, int day, int year);
setBirthDate(3, 1, 2012); // 1月3日还是3月1日？
//定义结构体类型
struct Day {
explicit Day(int d):val(d){} //设置为explicit，不能隐式转换
int val;
}
struct Month {
explicit Month(int d):val(d){} //设置为explicit，不能隐式转换
int val;
}
struct Year {
explicit Year(int d):val(d){} //设置为explicit，不能隐式转换
int val;
}
void setBirthDate(Month m, Day d, Year y);
setBirthDate(Month(3), Day(1), Year(2010)); //正确
setBirthDate(3, 1, 2010); // 编译不过，很难使用出错
//############################################################################
/* Template Specialization for STL
*
* Specialize the standard library templates' behavior for our class
*
* std:: is a special namespace where we are not allowed to alter its contents
* But we can specialize them for our types
*/
class collar;
class dog {
collar* pCollar;
dog(string name = "Bob") {pCollar = new collar(); cout << name << " is born." << endl; }
}
int main() {
dog dog1("Henry");
dog dog2("Boq");
std::swap(dog1, dog2);
}