switch для std::string C++

Question

Уважаемые Гуру, скажите, приемлим ли такой подход для практического применения:

#include <functional>
#include <iostream>
#include <memory>
#include <string>
#include <map>

class Base
{
public:
  Base() = default;
  virtual ~Base() = default;

  virtual void proc() = 0;
};

class Derived_1 : public Base
{
public:
  Derived_1() = default;
  virtual ~Derived_1() = default;

  virtual void proc() override 
  { return; }
};

class Derived_2 : public Base
{
public:
  Derived_2() = default;
  virtual ~Derived_2() = default;

  virtual void proc() override 
  { return; }
};

class Impl
{
  std::unique_ptr<Base> uptr_deriv;

public:
  Impl() = default;
  ~Impl() = default;

  void assign_uptr(std::string what)
  {
    using lambda = std::function<void()>;
    using msl = std::map<std::string, lambda>;

    std::unique_ptr<Base> uptr_temp;

    msl SWITCH_STR;
    SWITCH_STR["Derived_1"] =
      [&uptr_temp]()
      {
          std::cout << "Assigning Derived_1" << std::endl;
          uptr_temp = std::make_unique<Derived_1>();
      };
    SWITCH_STR["Derived_2"] =
      [&uptr_temp]()
      {
          std::cout << "Assigning Derived_2" << std::endl;
          uptr_temp = std::make_unique<Derived_2>();
      };
    SWITCH_STR[what]();

    uptr_deriv = std::move(uptr_temp);
  }
};

int main(int argc, char *argv[])
{
    Impl i;

    i.assign_uptr("Derived_1");
    i.assign_uptr("Derived_2");
    i.assign_uptr("Derived_1");
    i.assign_uptr("Derived_2");
    i.assign_uptr("Derived_1");
    i.assign_uptr("Derived_2");
}

Вывод:

Assigning Derived_1
Assigning Derived_2
Assigning Derived_1
Assigning Derived_2
Assigning Derived_1
Assigning Derived_2

Answer 1

посоревнуемся в знании толка? посоревнуемся

#include "string_case.hpp"
#include <iostream>

int
main(int const argc, char const * const * const pp_args)
{
    ::std::string some_arg{pp_args[1]};
    switch(_s, some_arg)
    {
        case "first"_s:
        {
            ::std::cout << "first case" << ::std::endl;
            break;
        }
        case "second"_s:
        {
            ::std::cout << "second case" << ::std::endl;
            break;
        }
        default:
        {
            ::std::cout << "default case" << ::std::endl;
            break;
        }
    }
    return 0;
}

online compiler

как оно работает (пишу пониже, чтобы читатель сразу не шарахался)

// string_case.hpp
#include <cstddef>
#include <string>

enum class
case_id
{   unknown
,   first
,   second
};

[[nodiscard]] constexpr auto
impl(char const * const psz) noexcept
{
    if(('f' == psz[0]) and ('i' == psz[1]) and ('r' == psz[2]) and ('s' == psz[3]) and ('t' == psz[4]) and ('\0' == psz[5]))
    {
        return case_id::first;
    }
    if(('s' == psz[0]) and ('e' == psz[1]) and ('c' == psz[2]) and ('o' == psz[3]) and ('n' == psz[4]) and ('d' == psz[5]) and ('\0' == psz[6]))
    {
        return case_id::second;
    }
    return case_id::unknown;
}

constexpr class
{
    public: [[nodiscard]] constexpr auto
    operator ,(char const * const psz) const noexcept
    {
        return impl(psz);
    }

    public: [[nodiscard]] case_id
    operator ,(::std::string const & s) const noexcept
    {
        return impl(s.c_str());
    }
} _s;

[[nodiscard]] constexpr auto 
operator ""_s(char const * const psz, [[maybe_unused]] ::std::size_t const size) noexcept
{
    return impl(psz);
}

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switch для std::string C++

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