vec_concat.hpp

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#ifndef STAN_MATH_PRIM_FUN_VEC_CONCAT_HPP
#define STAN_MATH_PRIM_FUN_VEC_CONCAT_HPP
 
#include <stan/math/prim/meta.hpp>
#include <type_traits>
#include <vector>
 
namespace stan {
namespace math {
namespace internal {
inline auto sum_vector_sizes() { return 0; }
template <typename Vec, typename... VecArgs>
inline auto sum_vector_sizes(const Vec& x, const VecArgs&... args) {
  return x.size() + sum_vector_sizes(args...);
}
template <typename VecInOut>
inline void append_vectors(VecInOut& x) {}
template <typename VecInOut, typename VecIn, typename... VecArgs>
inline void append_vectors(VecInOut& x, const VecIn& y,
                           const VecArgs&... args) {
  for (auto& yy : y) {
    x.push_back(yy);
  }
  append_vectors(x, args...);
}
}  // namespace internal
 
template <typename Vec, typename... Args>
inline auto vec_concat(const Vec& v1, const Args&... args) {
  Vec vec;
  vec.reserve(internal::sum_vector_sizes(v1, args...));
  internal::append_vectors(vec, v1, args...);
  return vec;
}
 
}  // namespace math
}  // namespace stan
 
#endif