src/hb-meta.hh

/*
 * Copyright © 2018  Google, Inc.
 *
 *  This is part of HarfBuzz, a text shaping library.
 *
 * Permission is hereby granted, without written agreement and without
 * license or royalty fees, to use, copy, modify, and distribute this
 * software and its documentation for any purpose, provided that the
 * above copyright notice and the following two paragraphs appear in
 * all copies of this software.
 *
 * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
 * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
 * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
 * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
 * DAMAGE.
 *
 * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
 * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
 * FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
 * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
 * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
 *
 * Google Author(s): Behdad Esfahbod
 */

#ifndef HB_META_HH
#define HB_META_HH

#include "hb.hh"


/*
 * C++ template meta-programming & fundamentals used with them.
 */

/* Void!  For when we need a expression-type of void. */
struct hb_empty_t {};

/* https://en.cppreference.com/w/cpp/types/void_t */
template<typename... Ts> struct _hb_void_t { typedef void type; };
template<typename... Ts> using hb_void_t = typename _hb_void_t<Ts...>::type;

template<typename Head, typename... Ts> struct _hb_head_t { typedef Head type; };
template<typename... Ts> using hb_head_t = typename _hb_head_t<Ts...>::type;

template <typename T, T v> struct hb_integral_constant { static constexpr T value = v; };
template <bool b> using hb_bool_constant = hb_integral_constant<bool, b>;
using hb_true_type = hb_bool_constant<true>;
using hb_false_type = hb_bool_constant<false>;

/* Static-assert as expression. */
template <bool cond> struct static_assert_expr;
template <> struct static_assert_expr<true> : hb_false_type {};
#define static_assert_expr(C) static_assert_expr<C>::value

/* Basic type SFINAE. */

template <bool B, typename T = void> struct hb_enable_if {};
template <typename T>                struct hb_enable_if<true, T> { typedef T type; };
#define hb_enable_if(Cond) typename hb_enable_if<(Cond)>::type* = nullptr
/* Concepts/Requires alias: */
#define hb_requires(Cond) hb_enable_if((Cond))

template <typename T, typename T2> struct hb_is_same : hb_false_type {};
template <typename T>              struct hb_is_same<T, T> : hb_true_type {};
#define hb_is_same(T, T2) hb_is_same<T, T2>::value

/* Function overloading SFINAE and priority. */

#define HB_RETURN(Ret, E) -> hb_head_t<Ret, decltype ((E))> { return (E); }
#define HB_AUTO_RETURN(E) -> decltype ((E)) { return (E); }
#define HB_VOID_RETURN(E) -> hb_void_t<decltype ((E))> { (E); }

template <unsigned Pri> struct hb_priority : hb_priority<Pri - 1> {};
template <>             struct hb_priority<0> {};
#define hb_prioritize hb_priority<16> ()

#define HB_FUNCOBJ(x) static_const x HB_UNUSED


template <typename T> struct hb_type_identity_t { typedef T type; };
template <typename T> using hb_type_identity = typename hb_type_identity_t<T>::type;

struct
{
  template <typename T> constexpr T*
  operator () (T& arg) const
  {
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wcast-align"
    /* https://en.cppreference.com/w/cpp/memory/addressof */
    return reinterpret_cast<T*> (
	     &const_cast<char&> (
		reinterpret_cast<const volatile char&> (arg)));
#pragma GCC diagnostic pop
  }
}
HB_FUNCOBJ (hb_addressof);

template <typename T> static inline T hb_declval ();
#define hb_declval(T) (hb_declval<T> ())

template <typename T> struct hb_match_const		: hb_type_identity_t<T>, hb_false_type	{};
template <typename T> struct hb_match_const<const T>	: hb_type_identity_t<T>, hb_true_type	{};
template <typename T> using hb_remove_const = typename hb_match_const<T>::type;
template <typename T> using hb_add_const = const T;
#define hb_is_const(T) hb_match_const<T>::value
template <typename T> struct hb_match_reference		: hb_type_identity_t<T>, hb_false_type	{};
template <typename T> struct hb_match_reference<T &>	: hb_type_identity_t<T>, hb_true_type	{};
template <typename T> struct hb_match_reference<T &&>	: hb_type_identity_t<T>, hb_true_type	{};
template <typename T> using hb_remove_reference = typename hb_match_reference<T>::type;
template <typename T> auto _hb_try_add_lvalue_reference (hb_priority<1>) -> hb_type_identity<T&>;
template <typename T> auto _hb_try_add_lvalue_reference (hb_priority<0>) -> hb_type_identity<T>;
template <typename T> using hb_add_lvalue_reference = decltype (_hb_try_add_lvalue_reference<T> (hb_prioritize));
template <typename T> auto _hb_try_add_rvalue_reference (hb_priority<1>) -> hb_type_identity<T&&>;
template <typename T> auto _hb_try_add_rvalue_reference (hb_priority<0>) -> hb_type_identity<T>;
template <typename T> using hb_add_rvalue_reference = decltype (_hb_try_add_rvalue_reference<T> (hb_prioritize));
#define hb_is_reference(T) hb_match_reference<T>::value
template <typename T> struct hb_match_pointer		: hb_type_identity_t<T>, hb_false_type	{};
template <typename T> struct hb_match_pointer<T *>	: hb_type_identity_t<T>, hb_true_type	{};
template <typename T> using hb_remove_pointer = typename hb_match_pointer<T>::type;
template <typename T> auto _hb_try_add_pointer (hb_priority<1>) -> hb_type_identity<hb_remove_reference<T>*>;
template <typename T> auto _hb_try_add_pointer (hb_priority<1>) -> hb_type_identity<T>;
template <typename T> using hb_add_pointer = decltype (_hb_try_add_pointer<T> (hb_prioritize));
#define hb_is_pointer(T) hb_match_pointer<T>::value


/* TODO Add feature-parity to std::decay. */
template <typename T> using hb_decay = hb_remove_const<hb_remove_reference<T>>;


template<bool B, class T, class F>
struct _hb_conditional { typedef T type; };
template<class T, class F>
struct _hb_conditional<false, T, F> { typedef F type; };
template<bool B, class T, class F>
using hb_conditional = typename _hb_conditional<B, T, F>::type;


template <typename From, typename To>
struct hb_is_convertible
{
  private:
  static constexpr bool   from_void = hb_is_same (void, hb_decay<From>);
  static constexpr bool     to_void = hb_is_same (void, hb_decay<To>  );
  static constexpr bool either_void = from_void || to_void;
  static constexpr bool   both_void = from_void && to_void;

  static hb_true_type impl2 (hb_conditional<to_void, int, To>);

  template <typename T>
  static auto impl (hb_priority<1>) -> decltype (impl2 (hb_declval (T)));
  template <typename T>
  static hb_false_type impl (hb_priority<0>);
  public:
  static constexpr bool value = both_void ||
		       (!either_void &&
			decltype (impl<hb_conditional<from_void, int, From>> (hb_prioritize))::value);
};
#define hb_is_convertible(From,To) hb_is_convertible<From, To>::value

template <typename Base, typename Derived>
using hb_is_base_of = hb_is_convertible<hb_decay<Derived> *, hb_decay<Base> *>;
#define hb_is_base_of(Base,Derived) hb_is_base_of<Base, Derived>::value

template <typename From, typename To>
using hb_is_cr_convertible = hb_bool_constant<
  hb_is_same (hb_decay<From>, hb_decay<To>) &&
  (!hb_is_const (From) || hb_is_const (To)) &&
  (!hb_is_reference (To) || hb_is_const (To) || hb_is_reference (To))
>;
#define hb_is_cr_convertible(From,To) hb_is_cr_convertible<From, To>::value

/* std::move and std::forward */

template <typename T>
static constexpr hb_remove_reference<T>&& hb_move (T&& t) { return (hb_remove_reference<T>&&) (t); }

template <typename T>
static constexpr T&& hb_forward (hb_remove_reference<T>& t) { return (T&&) t; }
template <typename T>
static constexpr T&& hb_forward (hb_remove_reference<T>&& t) { return (T&&) t; }

struct
{
  template <typename T> constexpr auto
  operator () (T&& v) const HB_AUTO_RETURN (hb_forward<T> (v))

  template <typename T> constexpr auto
  operator () (T *v) const HB_AUTO_RETURN (*v)
}
HB_FUNCOBJ (hb_deref);

struct
{
  template <typename T> constexpr auto
  operator () (T&& v) const HB_AUTO_RETURN (hb_forward<T> (v))

  template <typename T> constexpr auto
  operator () (T& v) const HB_AUTO_RETURN (hb_addressof (v))
}
HB_FUNCOBJ (hb_ref);

template <typename T>
struct hb_reference_wrapper
{
  hb_reference_wrapper (T v) : v (v) {}
  bool operator == (const hb_reference_wrapper& o) const { return v == o.v; }
  bool operator != (const hb_reference_wrapper& o) const { return v != o.v; }
  operator T () const { return v; }
  T get () const { return v; }
  T v;
};
template <typename T>
struct hb_reference_wrapper<T&>
{
  hb_reference_wrapper (T& v) : v (hb_addressof (v)) {}
  bool operator == (const hb_reference_wrapper& o) const { return v == o.v; }
  bool operator != (const hb_reference_wrapper& o) const { return v != o.v; }
  operator T& () const { return *v; }
  T& get () const { return *v; }
  T* v;
};


/* Type traits */

template <typename T>
using hb_is_integral = hb_bool_constant<
  hb_is_same (hb_decay<T>, char) ||
  hb_is_same (hb_decay<T>, signed char) ||
  hb_is_same (hb_decay<T>, unsigned char) ||
  hb_is_same (hb_decay<T>, signed int) ||
  hb_is_same (hb_decay<T>, unsigned int) ||
  hb_is_same (hb_decay<T>, signed short) ||
  hb_is_same (hb_decay<T>, unsigned short) ||
  hb_is_same (hb_decay<T>, signed long) ||
  hb_is_same (hb_decay<T>, unsigned long) ||
  hb_is_same (hb_decay<T>, signed long long) ||
  hb_is_same (hb_decay<T>, unsigned long long) ||
  false
>;
#define hb_is_integral(T) hb_is_integral<T>::value
template <typename T>
using hb_is_floating_point = hb_bool_constant<
  hb_is_same (hb_decay<T>, float) ||
  hb_is_same (hb_decay<T>, double) ||
  hb_is_same (hb_decay<T>, long double) ||
  false
>;
#define hb_is_floating_point(T) hb_is_floating_point<T>::value
template <typename T>
using hb_is_arithmetic = hb_bool_constant<
  hb_is_integral (T) ||
  hb_is_floating_point (T) ||
  false
>;
#define hb_is_arithmetic(T) hb_is_arithmetic<T>::value


template <typename T, bool is_arithmetic> struct hb_is_signed_;
template <typename T> struct hb_is_signed_<T, false>	: hb_false_type {};
template <typename T> struct hb_is_signed_<T, true>	: hb_bool_constant<(T) -1 < (T) 0> {};
template <typename T> struct hb_is_signed : hb_is_signed_<T, hb_is_arithmetic (T)> {};
#define hb_is_signed(T) hb_is_signed<T>::value
template <typename T, bool is_arithmetic> struct hb_is_unsigned_;
template <typename T> struct hb_is_unsigned_<T, false>	: hb_false_type {};
template <typename T> struct hb_is_unsigned_<T, true>	: hb_bool_constant<(T) 0 < (T) -1> {};
template <typename T> struct hb_is_unsigned : hb_is_unsigned_<T, hb_is_arithmetic (T)> {};
#define hb_is_unsigned(T) hb_is_unsigned<T>::value

template <typename T> struct hb_int_min;
template <> struct hb_int_min<char>			: hb_integral_constant<char,			CHAR_MIN>	{};
template <> struct hb_int_min<signed char>		: hb_integral_constant<signed char,		SCHAR_MIN>	{};
template <> struct hb_int_min<unsigned char>		: hb_integral_constant<unsigned char,		0>		{};
template <> struct hb_int_min<signed short>		: hb_integral_constant<signed short,		SHRT_MIN>	{};
template <> struct hb_int_min<unsigned short>		: hb_integral_constant<unsigned short,		0>		{};
template <> struct hb_int_min<signed int>		: hb_integral_constant<signed int,		INT_MIN>	{};
template <> struct hb_int_min<unsigned int>		: hb_integral_constant<unsigned int,		0>		{};
template <> struct hb_int_min<signed long>		: hb_integral_constant<signed long,		LONG_MIN>	{};
template <> struct hb_int_min<unsigned long>		: hb_integral_constant<unsigned long,		0>		{};
template <> struct hb_int_min<signed long long>		: hb_integral_constant<signed long long,	LLONG_MIN>	{};
template <> struct hb_int_min<unsigned long long>	: hb_integral_constant<unsigned long long,	0>		{};
template <typename T> struct hb_int_min<T *>		: hb_integral_constant<T *,			nullptr>	{};
#define hb_int_min(T) hb_int_min<T>::value
template <typename T> struct hb_int_max;
template <> struct hb_int_max<char>			: hb_integral_constant<char,			CHAR_MAX>	{};
template <> struct hb_int_max<signed char>		: hb_integral_constant<signed char,		SCHAR_MAX>	{};
template <> struct hb_int_max<unsigned char>		: hb_integral_constant<unsigned char,		UCHAR_MAX>	{};
template <> struct hb_int_max<signed short>		: hb_integral_constant<signed short,		SHRT_MAX>	{};
template <> struct hb_int_max<unsigned short>		: hb_integral_constant<unsigned short,		USHRT_MAX>	{};
template <> struct hb_int_max<signed int>		: hb_integral_constant<signed int,		INT_MAX>	{};
template <> struct hb_int_max<unsigned int>		: hb_integral_constant<unsigned int,		UINT_MAX>	{};
template <> struct hb_int_max<signed long>		: hb_integral_constant<signed long,		LONG_MAX>	{};
template <> struct hb_int_max<unsigned long>		: hb_integral_constant<unsigned long,		ULONG_MAX>	{};
template <> struct hb_int_max<signed long long>		: hb_integral_constant<signed long long,	LLONG_MAX>	{};
template <> struct hb_int_max<unsigned long long>	: hb_integral_constant<unsigned long long,	ULLONG_MAX>	{};
#define hb_int_max(T) hb_int_max<T>::value


/* Class traits. */

#define HB_DELETE_COPY_ASSIGN(TypeName) \
  TypeName(const TypeName&) = delete; \
  void operator=(const TypeName&) = delete
#define HB_DELETE_CREATE_COPY_ASSIGN(TypeName) \
  TypeName() = delete; \
  TypeName(const TypeName&) = delete; \
  void operator=(const TypeName&) = delete

template <typename T, typename>
struct _hb_is_destructible : hb_false_type {};
template <typename T>
struct _hb_is_destructible<T, hb_void_t<decltype (hb_declval (T).~T ())>> : hb_true_type {};
template <typename T>
using hb_is_destructible = _hb_is_destructible<T, void>;
#define hb_is_destructible(T) hb_is_destructible<T>::value

template <typename T, typename, typename ...Ts>
struct _hb_is_constructible : hb_false_type {};
template <typename T, typename ...Ts>
struct _hb_is_constructible<T, hb_void_t<decltype (T (hb_declval (Ts)...))>, Ts...> : hb_true_type {};
template <typename T, typename ...Ts>
using hb_is_constructible = _hb_is_constructible<T, void, Ts...>;
#define hb_is_constructible(...) hb_is_constructible<__VA_ARGS__>::value

template <typename T>
using hb_is_default_constructible = hb_is_constructible<T>;
#define hb_is_default_constructible(T) hb_is_default_constructible<T>::value

template <typename T>
using hb_is_copy_constructible = hb_is_constructible<T, hb_add_lvalue_reference<hb_add_const<T>>>;
#define hb_is_copy_constructible(T) hb_is_copy_constructible<T>::value

template <typename T>
using hb_is_move_constructible = hb_is_constructible<T, hb_add_rvalue_reference<hb_add_const<T>>>;
#define hb_is_move_constructible(T) hb_is_move_constructible<T>::value

template <typename T, typename U, typename>
struct _hb_is_assignable : hb_false_type {};
template <typename T, typename U>
struct _hb_is_assignable<T, U, hb_void_t<decltype (hb_declval (T) = hb_declval (U))>> : hb_true_type {};
template <typename T, typename U>
using hb_is_assignable = _hb_is_assignable<T, U, void>;
#define hb_is_assignable(T,U) hb_is_assignable<T, U>::value

template <typename T>
using hb_is_copy_assignable = hb_is_assignable<hb_add_lvalue_reference<T>,
					       hb_add_lvalue_reference<hb_add_const<T>>>;
#define hb_is_copy_assignable(T) hb_is_copy_assignable<T>::value

template <typename T>
using hb_is_move_assignable = hb_is_assignable<hb_add_lvalue_reference<T>,
					       hb_add_rvalue_reference<T>>;
#define hb_is_move_assignable(T) hb_is_move_assignable<T>::value

/* Trivial versions. */

template <typename T> union hb_trivial { T value; };

template <typename T>
using hb_is_trivially_destructible= hb_is_destructible<hb_trivial<T>>;
#define hb_is_trivially_destructible(T) hb_is_trivially_destructible<T>::value

/* Don't know how to do the following. */
//template <typename T, typename ...Ts>
//using hb_is_trivially_constructible= hb_is_constructible<hb_trivial<T>, hb_trivial<Ts>...>;
//#define hb_is_trivially_constructible(...) hb_is_trivially_constructible<__VA_ARGS__>::value

template <typename T>
using hb_is_trivially_default_constructible= hb_is_default_constructible<hb_trivial<T>>;
#define hb_is_trivially_default_constructible(T) hb_is_trivially_default_constructible<T>::value

template <typename T>
using hb_is_trivially_copy_constructible= hb_is_copy_constructible<hb_trivial<T>>;
#define hb_is_trivially_copy_constructible(T) hb_is_trivially_copy_constructible<T>::value

template <typename T>
using hb_is_trivially_move_constructible= hb_is_move_constructible<hb_trivial<T>>;
#define hb_is_trivially_move_constructible(T) hb_is_trivially_move_constructible<T>::value

/* Don't know how to do the following. */
//template <typename T, typename U>
//using hb_is_trivially_assignable= hb_is_assignable<hb_trivial<T>, hb_trivial<U>>;
//#define hb_is_trivially_assignable(T,U) hb_is_trivially_assignable<T, U>::value

template <typename T>
using hb_is_trivially_copy_assignable= hb_is_copy_assignable<hb_trivial<T>>;
#define hb_is_trivially_copy_assignable(T) hb_is_trivially_copy_assignable<T>::value

template <typename T>
using hb_is_trivially_move_assignable= hb_is_move_assignable<hb_trivial<T>>;
#define hb_is_trivially_move_assignable(T) hb_is_trivially_move_assignable<T>::value

template <typename T>
using hb_is_trivially_copyable= hb_bool_constant<
  hb_is_trivially_destructible (T) &&
  (!hb_is_move_assignable (T) || hb_is_trivially_move_assignable (T)) &&
  (!hb_is_move_constructible (T) || hb_is_trivially_move_constructible (T)) &&
  (!hb_is_copy_assignable (T) || hb_is_trivially_copy_assignable (T)) &&
  (!hb_is_copy_constructible (T) || hb_is_trivially_copy_constructible (T)) &&
  true
>;
#define hb_is_trivially_copyable(T) hb_is_trivially_copyable<T>::value

template <typename T>
using hb_is_trivial= hb_bool_constant<
  hb_is_trivially_copyable (T) &&
  hb_is_trivially_default_constructible (T)
>;
#define hb_is_trivial(T) hb_is_trivial<T>::value

/* hb_unwrap_type (T)
 * If T has no T::type, returns T. Otherwise calls itself on T::type recursively.
 */

template <typename T, typename>
struct _hb_unwrap_type : hb_type_identity_t<T> {};
template <typename T>
struct _hb_unwrap_type<T, hb_void_t<typename T::type>> : _hb_unwrap_type<typename T::type, void> {};
template <typename T>
using hb_unwrap_type = _hb_unwrap_type<T, void>;
#define hb_unwrap_type(T) typename hb_unwrap_type<T>::type

#endif /* HB_META_HH */