Dereference-Pattern.cpp

#include "matchit.h"
#include <iostream>
#include <memory>

struct Node
{
  int value;
  std::unique_ptr<Node> lhs, rhs;
};

bool operator==(Node const &lhs, Node const &rhs)
{
  return lhs.value == rhs.value && lhs.lhs == rhs.lhs && lhs.rhs == rhs.rhs;
}

void print_leftmost(const Node &node)
{
  auto deref = [](auto &&e) -> decltype(auto)
  { return *e; };
  using namespace matchit;
  Id<int> v;
  Id<Node> l;

  using N = Node;
  match(node)(
      pattern | and_(app(&N::value, v),
                     app(&N::lhs, nullptr)) = [&]
      { std::cout << *v << '\n'; },
      pattern | app(&N::lhs, app(deref, l)) = [&]
      { print_leftmost(*l); }
      //                                ˆˆˆˆˆˆˆˆˆˆˆˆˆ dereference pattern
  );
}

int32_t main()
{
  const auto n = Node{4, {}, {}};
  print_leftmost(n);

  return 0;
}