optional.h

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/*
 * Copyright (c) 2020 Roc Streaming authors
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */
 
//! @file roc_core/optional.h
//! @brief Optionally constructed object.
 
#ifndef ROC_CORE_OPTIONAL_H_
#define ROC_CORE_OPTIONAL_H_
 
#include "roc_core/aligned_storage.h"
#include "roc_core/attributes.h"
#include "roc_core/noncopyable.h"
#include "roc_core/panic.h"
#include "roc_core/stddefs.h"
 
namespace roc {
namespace core {
 
//! Optionally constructed object.
template <class T, size_t Size = sizeof(T)> class Optional : public NonCopyable<> {
public:
    Optional()
        : ptr_(NULL) {
    }
 
    ~Optional() {
        if (ptr_) {
            ptr_->~T();
        }
    }
 
    //! Set pointer to the newly created object, destroy old pointed object if set.
    //! @pre
    //!  @p ptr should be returned by associated placement new.
    void reset(T* ptr = NULL) {
        if (ptr_) {
            ptr_->~T();
        }
        if (ptr && (void*)ptr != storage_.memory()) {
            roc_panic("optional: attempt to set incorrect object");
        }
        ptr_ = ptr;
    }
 
    //! Get underlying object.
    T* get() const {
        return ptr_;
    }
 
    //! Get underlying object.
    T* operator->() const {
        if (ptr_ == NULL) {
            roc_panic("optional: attempt to dereference uninitialized object");
        }
        return ptr_;
    }
 
    //! Get underlying reference.
    T& operator*() const {
        if (ptr_ == NULL) {
            roc_panic("optional: attempt to dereference uninitialized object");
        }
        return *ptr_;
    }
 
    //! Convert to bool.
    operator const struct unspecified_bool *() const {
        return (const unspecified_bool*)ptr_;
    }
 
    //! Get object memory.
    //! @pre
    //!  Should be called before object is actually allocated.
    void* unallocated_memory() {
        if (ptr_) {
            roc_panic("optional: attempt to get memory after the object was created");
        }
        return storage_.memory();
    }
 
private:
    T* ptr_;
    AlignedStorage<Size> storage_;
};
 
} // namespace core
} // namespace roc
 
//! Placement new for core::Optional.
//! @note
//!  nothrow forces compiler to check for NULL return value before calling ctor.
template <class T, size_t Size>
inline void* operator new(size_t size, roc::core::Optional<T, Size>& opt) throw() {
    roc_panic_if_not(size <= Size);
    return opt.unallocated_memory();
}
 
//! Placement delete for core::Optional.
//! @note
//!  Compiler calls this if ctor throws in a placement new expression.
template <class T, size_t Size>
inline void operator delete(void*, roc::core::Optional<T, Size>&) throw() {
}
 
#endif // ROC_CORE_OPTIONAL_H_