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//===- Any.h - Generic type erased holder of any type -----------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
///
/// \file
/// This file provides Any, a non-template class modeled in the spirit of
/// std::any. The idea is to provide a type-safe replacement for C's void*.
/// It can hold a value of any copy-constructible copy-assignable type
///
//===----------------------------------------------------------------------===//
#ifndef LLVM_ADT_ANY_H
#define LLVM_ADT_ANY_H
#include "llvm/ADT/STLForwardCompat.h"
#include "llvm/Support/Compiler.h"
#include <cassert>
#include <memory>
#include <type_traits>
namespace llvm {
class LLVM_EXTERNAL_VISIBILITY Any {
// The `Typeid<T>::Id` static data member below is a globally unique
// identifier for the type `T`. It is explicitly marked with default
// visibility so that when `-fvisibility=hidden` is used, the loader still
// merges duplicate definitions across DSO boundaries.
// We also cannot mark it as `const`, otherwise msvc merges all definitions
// when lto is enabled, making any comparison return true.
template <typename T> struct TypeId { static char Id; };
struct StorageBase {
virtual ~StorageBase() = default;
virtual std::unique_ptr<StorageBase> clone() const = 0;
virtual const void *id() const = 0;
};
template <typename T> struct StorageImpl : public StorageBase {
explicit StorageImpl(const T &Value) : Value(Value) {}
explicit StorageImpl(T &&Value) : Value(std::move(Value)) {}
std::unique_ptr<StorageBase> clone() const override {
return std::make_unique<StorageImpl<T>>(Value);
}
const void *id() const override { return &TypeId<T>::Id; }
T Value;
private:
StorageImpl &operator=(const StorageImpl &Other) = delete;
StorageImpl(const StorageImpl &Other) = delete;
};
public:
Any() = default;
Any(const Any &Other)
: Storage(Other.Storage ? Other.Storage->clone() : nullptr) {}
// When T is Any or T is not copy-constructible we need to explicitly disable
// the forwarding constructor so that the copy constructor gets selected
// instead.
template <typename T,
std::enable_if_t<
std::conjunction<
std::negation<std::is_same<std::decay_t<T>, Any>>,
// We also disable this overload when an `Any` object can be
// converted to the parameter type because in that case,
// this constructor may combine with that conversion during
// overload resolution for determining copy
// constructibility, and then when we try to determine copy
// constructibility below we may infinitely recurse. This is
// being evaluated by the standards committee as a potential
// DR in `std::any` as well, but we're going ahead and
// adopting it to work-around usage of `Any` with types that
// need to be implicitly convertible from an `Any`.
std::negation<std::is_convertible<Any, std::decay_t<T>>>,
std::is_copy_constructible<std::decay_t<T>>>::value,
int> = 0>
Any(T &&Value) {
Storage =
std::make_unique<StorageImpl<std::decay_t<T>>>(std::forward<T>(Value));
}
Any(Any &&Other) : Storage(std::move(Other.Storage)) {}
Any &swap(Any &Other) {
std::swap(Storage, Other.Storage);
return *this;
}
Any &operator=(Any Other) {
Storage = std::move(Other.Storage);
return *this;
}
bool has_value() const { return !!Storage; }
void reset() { Storage.reset(); }
private:
// Only used for the internal llvm::Any implementation
template <typename T> bool isa() const {
if (!Storage)
return false;
return Storage->id() == &Any::TypeId<remove_cvref_t<T>>::Id;
}
template <class T> friend T any_cast(const Any &Value);
template <class T> friend T any_cast(Any &Value);
template <class T> friend T any_cast(Any &&Value);
template <class T> friend const T *any_cast(const Any *Value);
template <class T> friend T *any_cast(Any *Value);
template <typename T> friend bool any_isa(const Any &Value);
std::unique_ptr<StorageBase> Storage;
};
// Define the type id and initialize with a non-zero value.
// Initializing with a zero value means the variable can end up in either the
// .data or the .bss section. This can lead to multiple definition linker errors
// when some object files are compiled with a compiler that puts the variable
// into .data but they are linked to object files from a different compiler that
// put the variable into .bss. To prevent this issue from happening, initialize
// the variable with a non-zero value, which forces it to land in .data (because
// .bss is zero-initialized).
// See also https://github.com/llvm/llvm-project/issues/62270
template <typename T> char Any::TypeId<T>::Id = 1;
template <class T> T any_cast(const Any &Value) {
assert(Value.isa<T>() && "Bad any cast!");
return static_cast<T>(*any_cast<remove_cvref_t<T>>(&Value));
}
template <class T> T any_cast(Any &Value) {
assert(Value.isa<T>() && "Bad any cast!");
return static_cast<T>(*any_cast<remove_cvref_t<T>>(&Value));
}
template <class T> T any_cast(Any &&Value) {
assert(Value.isa<T>() && "Bad any cast!");
return static_cast<T>(std::move(*any_cast<remove_cvref_t<T>>(&Value)));
}
template <class T> const T *any_cast(const Any *Value) {
using U = remove_cvref_t<T>;
if (!Value || !Value->isa<U>())
return nullptr;
return &static_cast<Any::StorageImpl<U> &>(*Value->Storage).Value;
}
template <class T> T *any_cast(Any *Value) {
using U = std::decay_t<T>;
if (!Value || !Value->isa<U>())
return nullptr;
return &static_cast<Any::StorageImpl<U> &>(*Value->Storage).Value;
}
} // end namespace llvm
#endif // LLVM_ADT_ANY_H
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