Is there life without RTTI – 3

#include <memory>
#include <vector>
#include <random>

struct Stmt_RTTI { virtual ~Stmt_RTTI() = default; };

struct IfStmt_RTTI : Stmt_RTTI { };
struct ForStmt_RTTI : Stmt_RTTI { };

struct Stmt_WithEnum
{ 
  enum Type { IfStmt, ForStmt, DoStmt, WhileStmt };
  Stmt_WithEnum(Type kind) : m_kind { kind } { }
  virtual ~Stmt_WithEnum() = default;
  Type Kind() const { return m_kind; }

private:
  const Type m_kind;
};

namespace Solution1
{
  template <Stmt_WithEnum::Type K>
  struct type_from_kind;

  template <typename T>
  struct kind_from_type;

#define MAKE_STMT_TRAITS(t, k) \
  template <> struct Solution1::type_from_kind<k> \
  { \
    using type = t; \
  }; \
  template <> struct Solution1::kind_from_type<t> \
  { \
    static constexpr auto value = k; \
  };

  template <typename T, typename Kind, typename ...Kinds>
  bool IsA(T stmt, Kind kind, Kinds ...kinds) noexcept
  {
    return stmt &&
          ((stmt->Kind() == kind) || ... || (stmt->Kind() == kinds));
  }

  template <typename To, typename From>
       requires std::is_pointer_v<To>
    && requires { static_cast<To>(std::declval<From *>()); }
  auto dyn_cast(From *p) noexcept
  {
    using ResultType = std::remove_cvref_t<
      std::remove_pointer_t< std::remove_cvref_t<To> >
    >;

    return IsA(p, kind_from_type<ResultType>::value)
             ? static_cast<To>(p)
             : nullptr;
  }
}

struct IfStmt_WithEnum : Stmt_WithEnum
{
  IfStmt_WithEnum() : Stmt_WithEnum { Stmt_WithEnum::IfStmt } {} 

  static bool classof(const Stmt_WithEnum *p) noexcept
  {
    return p && p->Kind() == Stmt_WithEnum::IfStmt;
  }
};

MAKE_STMT_TRAITS(IfStmt_WithEnum, Stmt_WithEnum::IfStmt)

struct ForStmt_WithEnum : Stmt_WithEnum
{
  ForStmt_WithEnum() : Stmt_WithEnum { Stmt_WithEnum::ForStmt } {}

  static bool classof(const Stmt_WithEnum *p) noexcept
  {
    return p && p->Kind() == Stmt_WithEnum::ForStmt;
  }
};

MAKE_STMT_TRAITS(ForStmt_WithEnum, Stmt_WithEnum::ForStmt)

namespace Solution2
{
  template <typename To, typename From>
  bool IsA(From *p) noexcept
  {
    using ResultType = std::remove_cvref_t<
      std::remove_pointer_t< std::remove_cvref_t<To> >
    >;

    return ResultType::classof(p);
  }

  template <typename To, typename From>
       requires std::is_pointer_v<To>
    && requires { static_cast<To>(std::declval<From *>()); }
  auto dyn_cast(From *p) noexcept
  {
    using ResultType = std::remove_cvref_t<
      std::remove_pointer_t< std::remove_cvref_t<To> >
    >;

    return IsA<ResultType>(p) ? static_cast<To>(p) : nullptr;
  }
}

std::unique_ptr<Stmt_RTTI> factory_1()
{
  static std::mt19937_64 Generator { 0 };
  std::uniform_int_distribution d { 0, 1 };
  switch (d(Generator))
  {
  case 0:
    return std::make_unique<IfStmt_RTTI>();
  case 1:
    return std::make_unique<ForStmt_RTTI>();
  }

  std::terminate();
}

std::unique_ptr<Stmt_WithEnum> factory_2()
{
  static std::mt19937_64 Generator { 0 };
  std::uniform_int_distribution d { 0, 1 };
  switch (d(Generator))
  {
  case 0:
    return std::make_unique<IfStmt_WithEnum>();
  case 1:
    return std::make_unique<ForStmt_WithEnum>();
  }

  std::terminate();
}

static void StmtRTTI_Benchmark(benchmark::State& state) {
  std::vector<std::unique_ptr<Stmt_RTTI>> vec;
  const auto size = 1'000'000u;
  
  vec.reserve(size);
  for (size_t i = 0; i < size; ++i)
  {
    vec.push_back(factory_1());
  }

  // Code inside this loop is measured repeatedly
  for (auto _ : state)
  {
    for (const auto &stmt : vec)
    {
      if (auto ifStmt = dynamic_cast<const IfStmt_RTTI *>(stmt.get()))
      {
        // Make sure the variable is not optimized away by compiler
        benchmark::DoNotOptimize(ifStmt);
      }
      else if (auto forStmt = dynamic_cast<const ForStmt_RTTI *>(stmt.get()))
      {
        // Make sure the variable is not optimized away by compiler
        benchmark::DoNotOptimize(forStmt);
      }
    }
  }
}
// Register the function as a benchmark
BENCHMARK(StmtRTTI_Benchmark);

static void StmtWithEnum_Benchmark_1(benchmark::State& state) {
  std::vector<std::unique_ptr<Stmt_WithEnum>> vec;
  const auto size = 1'000'000u;
  
  vec.reserve(size);
  for (size_t i = 0; i < size; ++i)
  {
    vec.push_back(factory_2());
  }

  // Code inside this loop is measured repeatedly
  for (auto _ : state)
  {
    for (const auto &stmt : vec)
    {
      if (auto ifStmt = 
                 Solution1::dyn_cast<const IfStmt_WithEnum *>(stmt.get()))
      {
        // Make sure the variable is not optimized away by compiler
        benchmark::DoNotOptimize(ifStmt);
      }
      else if (auto forStmt = 
                 Solution1::dyn_cast<const ForStmt_WithEnum *>(stmt.get()))
      {
        // Make sure the variable is not optimized away by compiler
        benchmark::DoNotOptimize(forStmt);
      }
    }
  }
}
BENCHMARK(StmtWithEnum_Benchmark_1);

static void StmtWithEnum_Benchmark_2(benchmark::State& state) 
{
  std::vector<std::unique_ptr<Stmt_WithEnum>> vec;
  const auto size = 1'000'000u;
  
  vec.reserve(size);
  for (size_t i = 0; i < size; ++i)
  {
    vec.push_back(factory_2());
  }

  // Code inside this loop is measured repeatedly
  for (auto _ : state)
  {
    for (const auto &stmt : vec)
    {
      if (auto ifStmt = Solution2::dyn_cast<
                                     const IfStmt_WithEnum *>(stmt.get()))
      {
        // Make sure the variable is not optimized away by compiler
        benchmark::DoNotOptimize(ifStmt);
      }
      else if (auto forStmt = 
                 Solution2::dyn_cast<const ForStmt_WithEnum *>(stmt.get()))
      {
        // Make sure the variable is not optimized away by compiler
        benchmark::DoNotOptimize(forStmt);
      }
    }
  }
}
BENCHMARK(StmtWithEnum_Benchmark_2);