本篇介绍
本篇继续c 20的学习
传参
都知道在传递比较复杂的参数的时候，最好用const &，如果要支持左值应用和右值引用，那么就需要写一对函数支持重载了:
代码语言：javascript复制class DataHolder {
public:
void setData(const std::vector<int>& data) { m_data = data; }
void setData(std::vector<int>&& data) { m_data = std::move(data); }
private:
std::vector<int> m_data;
};这时候如果要简化，那么就可以按值传递:
代码语言：javascript复制class DataHolder {
public:
void setData(std::vector<int> data) { m_data = std::move(data); }
private:
std::vector<int> m_data;
};按左值引用传递会拷贝一次，按右值引用不拷贝，但是函数需要重载，而按值传递，也是左值引用传递会拷贝一次，按右值引用不拷贝，效果一样，而且还更简单。
Ref-Qualified
有时候有的方法希望是临时对象调用的，有的方法希望是非临时对象调用的，这时候可以按照如下方式操作:
代码语言：javascript复制class TextHolder {
public:
TextHolder(string text) : m_text { move(text) } {} const string& getText() const & { return m_text; } string&& getText() && { return move(m_text); }
private:
string m_text;
};inline
Since C 17, you can declare your static data members as inline. The benefit of this is that you do not have to allocate space for them in a source file
代码语言：javascript复制export class Spreadsheet {
// Omitted for brevity
private:
static inline size_t ms_counter { 0 };
};bit_cast
It effectively interprets the bits of the source object as if they are the bits of the target object. bit_cast() requires that the size of the source and target objects are the same and that both are trivially copyable
代码语言：javascript复制float asFloat { 1.23f };
auto asUint { bit_cast<unsigned int>(asFloat) };
if (bit_cast<float>(asUint) == asFloat) { cout << "Roundtrip success." << endl; }
