list.hpp

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#pragma once
 
#include "imports.h"
 
#include <iterator>
#include <type_traits>
 
namespace cppgres {
 
template <typename T = void *> struct list {
  explicit list(::List *l) : list_(l) {}
 
  struct iterator {
    using iterator_category = std::forward_iterator_tag;
    using value_type = T;
    using difference_type = std::ptrdiff_t;
 
    ::ListCell *cell = nullptr;
 
    T operator*() const {
      if constexpr (std::is_pointer_v<T>) {
        return static_cast<T>(lfirst(cell));
      } else if constexpr (std::is_same_v<T, ::Oid>) {
        return lfirst_oid(cell);
      } else {
        static_assert(std::is_same_v<T, int>, "unsupported list element type");
        return lfirst_int(cell);
      }
    }
 
    iterator &operator++() {
      ++cell;
      return *this;
    }
    iterator operator++(int) {
      auto ret = *this;
      ++cell;
      return ret;
    }
    bool operator==(const iterator &) const = default;
  };
 
  iterator begin() const { return {list_ == NIL ? nullptr : &list_->elements[0]}; }
  iterator end() const { return {list_ == NIL ? nullptr : &list_->elements[list_->length]}; }
 
  size_t size() const { return list_ == NIL ? 0 : static_cast<size_t>(list_->length); }
  bool empty() const { return list_ == NIL; }
 
  operator ::List *() const { return list_; }
 
private:
  ::List *list_;
};
 
} // namespace cppgres