Can we use parameter packs as std::vector initializers?
c++11, stdvector, variadic-templates
Solution
Yes, it is possible to use pack expansions inside initialiser lists. C++11 [temp.variadic]§4 allows this:
... Pack expansions can occur in the following contexts: ...
- In an initializer-list (8.5); the pattern is an initializer-clause.
No, there's no way to make a non-template typesafe variadic function. What you have is OK. There was a question about this recently.
Problem
I'm experimenting with C++11 (I've used old C++ so far) and I wrote the following code: ``` #include <iostream> #include <vector> #include <type_traits> using namespace std; constexpr bool all_true(){ return true; } template <typename Head, typename... Tail> constexpr bool all_true(Head head, Tail... tail){ static_assert( is_convertible<bool, Head>::value, "all_true arguments must be convertible to bool!"); return static_cast<bool>(head) && all_true(tail...); } template<typename T, typename... Args> void print_as(Args... args){ static_assert( all_true(is_convertible<T,Args>::value...), "all arguments must be convertible to the specified type!"); vector<T> v {static_cast<T>(args)...}; for(T i : v) cout << i << endl; } int main(){ print_as<bool>(1, 2, 0, 4.1); } ``` The code compiles and runs as expected (I used gcc 4.6). I would like to aks the following questions: - I initialized a std::vector with an expanded parameter pack ( vector v {static_cast(args)...}; ). Is this correct C++11? I haven't found this feature explained anywhere. I don't like too much the declaration of all_true because I know the type but I use templates. Is it possible to use something similar to the following? ``` constexpr bool all_true(bool head, bool... tail){...} // This code doesn't compile ``` Thanks!