//
// Copyright 2017 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// -----------------------------------------------------------------------------
// any.h
// -----------------------------------------------------------------------------
//
// This header file define the `absl::any` type for holding a type-safe value
// of any type. The 'absl::any` type is useful for providing a way to hold
// something that is, as yet, unspecified. Such unspecified types
// traditionally are passed between API boundaries until they are later cast to
// their "destination" types. To cast to such a destination type, use
// `absl::any_cast()`. Note that when casting an `absl::any`, you must cast it
// to an explicit type; implicit conversions will throw.
//
// Example:
//
// auto a = absl::any(65);
// absl::any_cast<int>(a); // 65
// absl::any_cast<char>(a); // throws absl::bad_any_cast
// absl::any_cast<std::string>(a); // throws absl::bad_any_cast
//
// `absl::any` is a C++11 compatible version of the C++17 `std::any` abstraction
// and is designed to be a drop-in replacement for code compliant with C++17.
//
// Traditionally, the behavior of casting to a temporary unspecified type has
// been accomplished with the `void *` paradigm, where the pointer was to some
// other unspecified type. `absl::any` provides an "owning" version of `void *`
// that avoids issues of pointer management.
//
// Note: just as in the case of `void *`, use of `absl::any` (and its C++17
// version `std::any`) is a code smell indicating that your API might not be
// constructed correctly. We have seen that most uses of `any` are unwarranted,
// and `absl::any`, like `std::any`, is difficult to use properly. Before using
// this abstraction, make sure that you should not instead be rewriting your
// code to be more specific.
//
// Abseil expects to release an `absl::variant` type shortly (a C++11 compatible
// version of the C++17 `std::variant), which is generally preferred for use
// over `absl::any`.
#ifndef ABSL_TYPES_ANY_H_
#define ABSL_TYPES_ANY_H_
#include "absl/base/config.h"
#include "absl/utility/utility.h"
#ifdef ABSL_HAVE_STD_ANY
#include <any>
namespace absl {
using std::any;
using std::any_cast;
using std::bad_any_cast;
using std::make_any;
} // namespace absl
#else // ABSL_HAVE_STD_ANY
#include <algorithm>
#include <cstddef>
#include <initializer_list>
#include <memory>
#include <stdexcept>
#include <type_traits>
#include <typeinfo>
#include <utility>
#include "absl/base/macros.h"
#include "absl/meta/type_traits.h"
#include "absl/types/bad_any_cast.h"
// NOTE: This macro is an implementation detail that is undefined at the bottom
// of the file. It is not intended for expansion directly from user code.
#ifdef ABSL_ANY_DETAIL_HAS_RTTI
#error ABSL_ANY_DETAIL_HAS_RTTI cannot be directly set
#elif !defined(__GNUC__) || defined(__GXX_RTTI)
#define ABSL_ANY_DETAIL_HAS_RTTI 1
#endif // !defined(__GNUC__) || defined(__GXX_RTTI)
namespace absl {
namespace any_internal {
// FastTypeId<Type>() evaluates at compile/link-time to a unique integer for the
// passed in type. Their values are neither contiguous nor small, making them
// unfit for using as an index into a vector, but a good match for keys into
// maps or straight up comparisons.
// Note that on 64-bit (unix) systems size_t is 64-bit while int is 32-bit and
// the compiler will happily and quietly assign such a 64-bit value to a
// 32-bit integer. While a client should never do that it SHOULD still be safe,
// assuming the BSS segment doesn't span more than 4GiB.
template<typename Type>
inline size_t FastTypeId() {
static_assert(sizeof(char*) <= sizeof(size_t),
"ptr size too large for size_t");
// This static variable isn't actually used, only its address, so there are
// no concurrency issues.
static char dummy_var;
return reinterpret_cast<size_t>(&dummy_var);
}
} // namespace any_internal
class any;
// swap()
//
// Swaps two `absl::any` values. Equivalent to `x.swap(y) where `x` and `y` are
// `absl::any` types.
void swap(any& x, any& y) noexcept;
// make_any()
//
// Constructs an `absl::any` of type `T` with the given arguments.
template <typename T, typename... Args>
any make_any(Args&&... args);
// Overload of `absl::make_any()` for constructing an `absl::any` type from an
// initializer list.
template <typename T, typename U, typename... Args>
any make_any(std::initializer_list<U> il, Args&&... args);
// any_cast()
//
// Statically casts the value of a `const absl::any` type to the given type.
// This function will throw `absl::bad_any_cast` if the stored value type of the
// `absl::any` does not match the cast.
//
// `any_cast()` can also be used to get a reference to the internal storage iff
// a reference type is passed as its `ValueType`:
//
// Example:
//
// absl::any my_any = std::vector<int>();
// absl::any_cast<std::vector<int>&>(my_any).push_back(42);
template <typename ValueType>
ValueType any_cast(const any& operand);
// Overload of `any_cast()` to statically cast the value of a non-const
// `absl::any` type to the given type. This function will throw
// `absl::bad_any_cast` if the stored value type of the `absl::any` does not
// match the cast.
template <typename ValueType>
ValueType any_cast(any& operand); // NOLINT(runtime/references)
// Overload of `any_cast()` to statically cast the rvalue of an `absl::any`
// type. This function will throw `absl::bad_any_cast` if the stored value type
// of the `absl::any` does not match the cast.
template <typename ValueType>
ValueType any_cast(any&& operand);
// Overload of `any_cast()` to statically cast the value of a const pointer
// `absl::any` type to the given pointer type, or `nullptr` if the stored value
// type of the `absl::any` does not match the cast.
template <typename ValueType>
const ValueType* any_cast(const any* operand) noexcept;
// Overload of `any_cast()` to statically cast the value of a pointer
// `absl::any` type to the given pointer type, or `nullptr` if the stored value
// type of the `absl::any` does not match the cast.
template <typename ValueType>
ValueType* any_cast(any* operand) noexcept;
// any
//
// An `absl::any` object provides the facility to either store an instance of a
// type, known as the "contained object", or no value. An `absl::any` is used to
// store values of types that are unknown at compile time. The `absl::any`
// object, when containing a value, must contain a value type; storing a
// reference type is neither desired nor supported.
//
// An `absl::any` can only store a type that is copy-constructable; move-only
// types are not allowed within an `any` object.
//
// Example:
//
// auto a = absl::any(65); // Literal, copyable
// auto b = absl::any(std::vector<int>()); // Default-initialized, copyable
// std::unique_ptr<Foo> my_foo;
// auto c = absl::any(std::move(my_foo)); // Error, not copy-constructable
//
// Note that `absl::any` makes use of decayed types (`absl::decay_t` in this
// context) to remove const-volative qualifiers (known as "cv qualifiers"),
// decay functions to function pointers, etc. We essentially "decay" a given
// type into its essential type.
//
// `absl::any` makes use of decayed types when determing the basic type `T` of
// the value to store in the any's contained object. In the documentation below,
// we explcitly denote this by using the phrase "a decayed type of `T`".
//
// Example:
//
// const int a = 4;
// absl::any foo(a); // Decay ensures we store an "int", not a "const int&".
//
// void my_function() {}
// absl::any bar(my_function); // Decay ensures we store a function pointer.
//
// `absl::any` is a C++11 compatible version of the C++17 `std::any` abstraction
// and is designed to be a drop-in replacement for code compliant with C++17.
class any {
private:
template <typename T>
struct IsInPlaceType;
public:
// Constructors
// Constructs an empty `absl::any` object (`any::has_value()` will return
// `false`).
constexpr any() noexcept;
// Copy constructs an `absl::any` object with a "contained object" of the
// passed type of `other` (or an empty `absl::any` if `other.has_value()` is
// `false`.
any(const any& other)
: obj_(other.has_value() ? other.obj_->Clone()
: std::unique_ptr<ObjInterface>()) {}
// Move constructs an `absl::any` object with a "contained object" of the
// passed type of `other` (or an empty `absl::any` if `other.has_value()` is
// `false`).
any(any&& other) noexcept = default;
// Constructs an `absl::any` object with a "contained object" of the decayed
// type of `T`, which is initialized via `std::forward<T>(value)`.
//
// This constructor will not participate in overload resolution if the
// decayed type of `T` is not copy-constructible.
template <
typename T, typename VT = absl::decay_t<T>,
absl::enable_if_t<!absl::disjunction<
std::is_same<any, VT>, IsInPlaceType<VT>,
absl::negation<std::is_copy_constructible<VT> > >::value>* = nullptr>
any(T&& value) : obj_(new Obj<VT>(in_place, std::forward<T>(value))) {}
// Constructs an `absl::any` object with a "contained object" of the decayed
// type of `T`, which is initialized via `std::forward<T>(value)`.
template <typename T, typename... Args, typename VT = absl::decay_t<T>,
absl::enable_if_t<absl::conjunction<
std::is_copy_constructible<VT>,
std::is_constructible<VT, Args...>>::value>* = nullptr>
explicit any(in_place_type_t<T> /*tag*/, Args&&... args)
: obj_(new Obj<VT>(in_place, std::forward<Args>(args)...)) {}
// Constructs an `absl::any` object with a "contained object" of the passed
// type `VT` as a decayed type of `T`. `VT` is initialized as if
// direct-non-list-initializing an object of type `VT` with the arguments
// `initializer_list, std::forward<Args>(args)...`.
template <
typename T, typename U, typename... Args, typename VT = absl::decay_t<T>,
absl::enable_if_t<
absl::conjunction<std::is_copy_constructible<VT>,
std::is_constructible<VT, std::initializer_list<U>&,
Args...>>::value>* = nullptr>
explicit any(in_place_type_t<T> /*tag*/, std::initializer_list<U> ilist,
Args&&... args)
: obj_(new Obj<VT>(in_place, ilist, std::forward<Args>(args)...)) {}
// Assignment operators
// Copy assigns an `absl::any` object with a "contained object" of the
// passed type.
any& operator=(const any& rhs) {
any(rhs).swap(*this);
return *this;
}
// Move assigns an `absl::any` object with a "contained object" of the
// passed type. `rhs` is left in a valid but otherwise unspecified state.
any& operator=(any&& rhs) noexcept {
any(std::move(rhs)).swap(*this);
return *this;
}
// Assigns an `absl::any` object with a "contained object" of the passed type.
template <typename T, typename VT = absl::decay_t<T>,
absl::enable_if_t<absl::conjunction<
absl::negation<std::is_same<VT, any>>,
std::is_copy_constructible<VT>>::value>* = nullptr>
any& operator=(T&& rhs) {
any tmp(in_place_type_t<VT>(), std::forward<T>(rhs));
tmp.swap(*this);
return *this;
}
// Modifiers
// any::emplace()
//
// Emplaces a value within an `absl::any` object by calling `any::reset()`,
// initializing the contained value as if direct-non-list-initializing an
// object of type `VT` with the arguments `std::forward<Args>(args)...`, and
// returning a reference to the new contained value.
//
// Note: If an exception is thrown during the call to `VT`’s constructor,
// `*this` does not contain a value, and any previously contained value has
// been destroyed.
template <
typename T, typename... Args, typename VT = absl::decay_t<T>,
absl::enable_if_t<std::is_copy_constructible<VT>::value &&
std::is_constructible<VT, Args...>::value>* = nullptr>
VT& emplace(Args&&... args) {
reset(); // NOTE: reset() is required here even in the world of exceptions.
Obj<VT>* const object_ptr =
new Obj<VT>(in_place, std::forward<Args>(args)...);
obj_ = std::unique_ptr<ObjInterface>(object_ptr);
return object_ptr->value;
}
// Overload of `any::emplace()` to emplace a value within an `absl::any`
// object by calling `any::reset()`, initializing the contained value as if
// direct-non-list-initializing an object of type `VT` with the arguments
// `initilizer_list, std::forward<Args>(args)...`, and returning a reference
// to the new contained value.
//
// Note: If an exception is thrown during the call to `VT`’s constructor,
// `*this` does not contain a value, and any previously contained value has
// been destroyed. The function shall not participate in overload resolution
// unless `is_copy_constructible_v<VT>` is `true` and
// `is_constructible_v<VT, initializer_list<U>&, Args...>` is `true`.
template <
typename T, typename U, typename... Args, typename VT = absl::decay_t<T>,
absl::enable_if_t<std::is_copy_constructible<VT>::value &&
std::is_constructible<VT, std::initializer_list<U>&,
Args...>::value>* = nullptr>
VT& emplace(std::initializer_list<U> ilist, Args&&... args) {
reset(); // NOTE: reset() is required here even in the world of exceptions.
Obj<VT>* const object_ptr =
new Obj<VT>(in_place, ilist, std::forward<Args>(args)...);
obj_ = std::unique_ptr<ObjInterface>(object_ptr);
return object_ptr->value;
}
// any::reset()
//
// Resets the state of the `absl::any` object, destroying the contained object
// if present.
void reset() noexcept { obj_ = nullptr; }
// any::swap()
//
// Swaps the passed value and the value of this `absl::any` object.
void swap(any& other) noexcept { obj_.swap(other.obj_); }
// Observors
// any::has_value()
//
// Returns `true` if the `any` object has a contained value, otherwise
// returns `false`.
bool has_value() const noexcept { return obj_ != nullptr; }
#if ABSL_ANY_DETAIL_HAS_RTTI
// Returns: typeid(T) if *this has a contained object of type T, otherwise
// typeid(void).
const std::type_info& type() const noexcept {
if (has_value()) {
return obj_->Type();
}
return typeid(void);
}
#endif // ABSL_ANY_DETAIL_HAS_RTTI
private:
// Tagged type-erased abstraction for holding a cloneable object.
class ObjInterface {
public:
virtual ~ObjInterface() = default;
virtual std::unique_ptr<ObjInterface> Clone() const = 0;
virtual size_t type_id() const noexcept = 0;
#if ABSL_ANY_DETAIL_HAS_RTTI
virtual const std::type_info& Type() const noexcept = 0;
#endif // ABSL_ANY_DETAIL_HAS_RTTI
};
// Hold a value of some queryable type, with an ability to Clone it.
template <typename T>
class Obj : public ObjInterface {
public:
template <typename... Args>
explicit Obj(in_place_t /*tag*/, Args&&... args)
: value(std::forward<Args>(args)...) {}
std::unique_ptr<ObjInterface> Clone() const final {
return std::unique_ptr<ObjInterface>(new Obj(in_place, value));
}
size_t type_id() const noexcept final { return IdForType<T>(); }
#if ABSL_ANY_DETAIL_HAS_RTTI
const std::type_info& Type() const noexcept final { return typeid(T); }
#endif // ABSL_ANY_DETAIL_HAS_RTTI
T value;
};
std::unique_ptr<ObjInterface> CloneObj() const {
if (!obj_) return nullptr;
return obj_->Clone();
}
template <typename T>
static size_t IdForType() {
// Note: This type dance is to make the behavior consistent with typeid.
using NormalizedType =
typename std::remove_cv<typename std::remove_reference<T>::type>::type;
return any_internal::FastTypeId<NormalizedType>();
}
size_t GetObjTypeId() const {
return obj_ == nullptr ? any_internal::FastTypeId<void>() : obj_->type_id();
}
// `absl::any` nonmember functions //
// Description at the declaration site (top of file).
template <typename ValueType>
friend ValueType any_cast(const any& operand);
// Description at the declaration site (top of file).
template <typename ValueType>
friend ValueType any_cast(any& operand); // NOLINT(runtime/references)
// Description at the declaration site (top of file).
template <typename T>
friend const T* any_cast(const any* operand) noexcept;
// Description at the declaration site (top of file).
template <typename T>
friend T* any_cast(any* operand) noexcept;
std::unique_ptr<ObjInterface> obj_;
};
// -----------------------------------------------------------------------------
// Implementation Details
// -----------------------------------------------------------------------------
constexpr any::any() noexcept = default;
template <typename T>
struct any::IsInPlaceType : std::false_type {};
template <typename T>
struct any::IsInPlaceType<in_place_type_t<T>> : std::true_type {};
inline void swap(any& x, any& y) noexcept { x.swap(y); }
// Description at the declaration site (top of file).
template <typename T, typename... Args>
any make_any(Args&&... args) {
return any(in_place_type_t<T>(), std::forward<Args>(args)...);
}
// Description at the declaration site (top of file).
template <typename T, typename U, typename... Args>
any make_any(std::initializer_list<U> il, Args&&... args) {
return any(in_place_type_t<T>(), il, std::forward<Args>(args)...);
}
// Description at the declaration site (top of file).
template <typename ValueType>
ValueType any_cast(const any& operand) {
using U = typename std::remove_cv<
typename std::remove_reference<ValueType>::type>::type;
static_assert(std::is_constructible<ValueType, const U&>::value,
"Invalid ValueType");
auto* const result = (any_cast<U>)(&operand);
if (result == nullptr) {
any_internal::ThrowBadAnyCast();
}
return static_cast<ValueType>(*result);
}
// Description at the declaration site (top of file).
template <typename ValueType>
ValueType any_cast(any& operand) { // NOLINT(runtime/references)
using U = typename std::remove_cv<
typename std::remove_reference<ValueType>::type>::type;
static_assert(std::is_constructible<ValueType, U&>::value,
"Invalid ValueType");
auto* result = (any_cast<U>)(&operand);
if (result == nullptr) {
any_internal::ThrowBadAnyCast();
}
return static_cast<ValueType>(*result);
}
// Description at the declaration site (top of file).
template <typename ValueType>
ValueType any_cast(any&& operand) {
using U = typename std::remove_cv<
typename std::remove_reference<ValueType>::type>::type;
static_assert(std::is_constructible<ValueType, U>::value,
"Invalid ValueType");
return static_cast<ValueType>(std::move((any_cast<U&>)(operand)));
}
// Description at the declaration site (top of file).
template <typename T>
const T* any_cast(const any* operand) noexcept {
return operand && operand->GetObjTypeId() == any::IdForType<T>()
? std::addressof(
static_cast<const any::Obj<T>*>(operand->obj_.get())->value)
: nullptr;
}
// Description at the declaration site (top of file).
template <typename T>
T* any_cast(any* operand) noexcept {
return operand && operand->GetObjTypeId() == any::IdForType<T>()
? std::addressof(
static_cast<any::Obj<T>*>(operand->obj_.get())->value)
: nullptr;
}
} // namespace absl
#undef ABSL_ANY_DETAIL_HAS_RTTI
#endif // ABSL_HAVE_STD_ANY
#endif // ABSL_TYPES_ANY_H_
