RAII

这个太多例子了，不细说

公开Base的内容

#include <iostream>
using namespace std;struct Base
{Base(){container++;}
protected:int container = 0;
};struct Derived:public Base
{Derived(Base b):Base(b){}using Base::container;
};int main()
{Base a;cout<<Derived(a).container<<endl;
}

举个实际的例子

// Extracts a reference to the container from back_insert_iterator.
template <typename Container>
inline auto get_container(std::back_insert_iterator<Container> it)-> Container& {using base = std::back_insert_iterator<Container>;struct accessor : base {accessor(base b) : base(b) {}using base::container;};return *accessor(it).container;
}

对泛化类模板进行特化以达到编译期约束

template <typename T> struct is_char : std::false_type {};
template <> struct is_char<char> : std::true_type {}; 

对泛化类模板进行继承以达到编译期约束

struct compile_string {};
template <typename S>
struct is_compile_string : std::is_base_of<compile_string, S> {};

对返回值进行SFINAE达到编译期约束

#include <iostream>
#include <type_traits>template <typename T>
typename std::enable_if<std::is_integral<T>::value, void>::type
printValue(T value) {std::cout << "Integral value: " << value << std::endl;
}template <typename T>
typename std::enable_if<std::is_floating_point<T>::value, void>::type
printValue(T value) {std::cout << "Floating point value: " << value << std::endl;
}int main() {printValue(42);       // 调用第一个重载，输出：Integral value: 42printValue(3.14);     // 调用第二个重载，输出：Floating point value: 3.14printValue("hello");  // 不匹配任何重载，编译时不会产生错误return 0;
}

区分编译期与运行期

template <typename Char, typename InputIt, typename OutputIt>
constexpr auto copy_str(InputIt begin, InputIt end, OutputIt out)-> OutputIt {while (begin != end) *out++ = static_cast<Char>(*begin++);return out;
}template <typename Char, typename T, typename U,std::enable_if_t<std::is_same<remove_const_t<T>, U>::value&& is_char<U>::value>>
constexpr auto copy_str(T* begin, T* end, U* out) -> U* {if (is_constant_evaluated()) return copy_str<Char, T*, U*>(begin, end, out);auto size = to_unsigned(end - begin);if (size > 0) memcpy(out, begin, size * sizeof(U));return out + size;
}

对类模板进行调用达到接口约束

template <typename Char, typename Handler>
FMT_CONSTEXPR auto parse_replacement_field(const Char* begin, const Char* end,Handler&& handler) -> const Char* {struct id_adapter {Handler& handler;int arg_id;FMT_CONSTEXPR void on_auto() { arg_id = handler.on_arg_id(); }FMT_CONSTEXPR void on_index(int id) { arg_id = handler.on_arg_id(id); }FMT_CONSTEXPR void on_name(basic_string_view<Char> id) {arg_id = handler.on_arg_id(id);}};++begin;if (begin == end) return handler.on_error("invalid format string"), end;if (*begin == '}') {handler.on_replacement_field(handler.on_arg_id(), begin);} else if (*begin == '{') {handler.on_text(begin, begin + 1);} else {auto adapter = id_adapter{handler, 0};

只是这一段，对于Handler的接口约束就有很多了，而且都是必须实现的。