稀奇古怪的新特性，菜鸟在此啄上一啄。
1.
When should literal classes be used in C++?
2.
int i; // not constant
const int size = i; // fine! 可以，但为什么不在这里就先判断出问题的隐患呢？
int arr[size]; // Error!
然而对于constexpr，则表明这个值不仅是constant的，而且也是编译期确定的
int i; // not constant
constexpr int size = i; // Error!
于是，constexpr修饰的变量是可以表示数组大小的。
放在 stack上的数组也是可以的，比如main中的如下：
int main()
{
int i;
cin >> i;
int arr[i];
}跟const无关，而是使用了C99的一个特性，名叫variable length array（简称VLA）。
而为什么我们需要constexpr呢？那就是为了性能。
3.
Want speed? Use constexpr meta-programming!
static的方式是最快的。
4.
When should you use constexpr capability in C++11?
Suppose it does something a little more complicated.
constexpr int MeaningOfLife ( int a, int b ) { return a * b; }
const int meaningOfLife = MeaningOfLife( 6, 7 );
使用组合！
Now you have something that can be evaluated down to a constant while maintaining good readability and allowing slightly more complex processing than just setting a constant to a number.
It basically provides a good aid to maintainability as it becomes more obvious what you are doing. Take max( a, b ) for example:
template< typename Type > constexpr Type max( Type a, Type b ) { return a < b ? b : a; }
替代模板计算的一个很好的方式！效率比模板高。
Literal Type
|
down voteaccepted |
The defintion of "literal type" is in [basic.types] (C++11 3.9):
Literal types are broadly speaking the types that are permitted to occur as and in constant expressions. There is a trait, |
是否是literal type?
// is_literal_type example
#include <iostream>
#include <type_traits>
struct A { };
struct B { ~B(){} };
int main() {
std::cout << std::boolalpha;
std::cout << "is_literal_type:" << std::endl;
std::cout << "int: " << std::is_literal_type<int>::value << std::endl;
std::cout << "int&: " << std::is_literal_type<int&>::value << std::endl;
std::cout << "int*: " << std::is_literal_type<int*>::value << std::endl;
std::cout << "A: " << std::is_literal_type<A>::value << std::endl;
std::cout << "B: " << std::is_literal_type<B>::value << std::endl;
return 0;
}
Output:
is_literal_type: int: true int&: true int*: true A: true B: false |
一些问题：
constexpr vs template for compile-time maths functions?
元编程
泛型编程
continue...