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This seems to be a very simple question: How does one remove the first (the n-th) type in a std::tuple?
Example:
typedef std::tuple<int, short, double> tuple1; typedef std::tuple<short, double> tuple2; The operation described above would transform tuple1 into tuple2. Is it possible?
235
Class template std::tuple is a fixed-size collection of heterogeneous values. It is a generalization of std::pair. If std::is_trivially_destructible<Ti>::value is true for every Ti in Types , the destructor of tuple is trivial.
Tuples are immutable. Lists are mutable. Tuples can contain different data types. Lists consist of a singular data type.
Tuples are convenient in many circumstances. For instance, tuples make it easy to define functions that return more than one value. Some programming languages, such as ML, Python and Haskell, have built-in tuple constructs. Unfortunately C++ does not.
get(): get() is used to access the tuple values and modify them, it accepts the index and tuple name as arguments to access a particular tuple element. 2. make_tuple(): make_tuple() is used to assign tuple with values. The values passed should be in order with the values declared in the tuple.
You can use a simple type function based on partial specialization of a class template:
#include <type_traits> #include <tuple> using namespace std; template<typename T> struct remove_first_type { }; template<typename T, typename... Ts> struct remove_first_type<tuple<T, Ts...>> { typedef tuple<Ts...> type; }; int main() { typedef tuple<int, bool, double> my_tuple; typedef remove_first_type<my_tuple>::type my_tuple_wo_first_type; static_assert( is_same<my_tuple_wo_first_type, tuple<bool, double>>::value, "Error!" ); } Also, this solution can be easily generalized to remove the i-th type of a tuple:
#include <type_traits> #include <tuple> using namespace std; template<size_t I, typename T> struct remove_ith_type { }; template<typename T, typename... Ts> struct remove_ith_type<0, tuple<T, Ts...>> { typedef tuple<Ts...> type; }; template<size_t I, typename T, typename... Ts> struct remove_ith_type<I, tuple<T, Ts...>> { typedef decltype( tuple_cat( declval<tuple<T>>(), declval<typename remove_ith_type<I - 1, tuple<Ts...>>::type>() ) ) type; }; int main() { typedef tuple<int, bool, double> my_tuple; typedef remove_ith_type<1, my_tuple>::type my_tuple_wo_2nd_type; static_assert( is_same<my_tuple_wo_2nd_type, tuple<int, double>>::value, "Error!" ); } If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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