placeholder.hpp

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#pragma once
#include "operator_precedence.hpp"
#include "placeholder_expression.hpp"
#include <concepts>
#include <ostream>
#include <tuple>
#include <type_traits>

namespace xtd {
  namespace expressions {
    template <size_t index>
    struct placeholder : placeholder_expression {
      
      static constexpr operator_precedence precedence = operator_precedence::placeholder;

      
      placeholder() = default;

      
      template <typename... args_t>
      constexpr decltype(auto) operator()(args_t&&... args) const {
        return std::get<index - 1>(std::forward_as_tuple(std::forward<args_t>(args)...));
      }

    };

    template <size_t index>
    constexpr auto expression::placeholder() {return xtd::expressions::placeholder<index> {};}
 
    template <size_t index>
    inline auto operator <<(std::ostream& os, const placeholder<index>&) -> std::ostream& {return os << "_" << index;}
  }
}