checked_pointer.hpp

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#pragma once
 
/// @file userver/utils/checked_pointer.hpp
/// @brief @copybrief utils::CheckedPtr
 
#include <cstdlib>
#include <stdexcept>
 
#include <userver/utils/assert.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace utils {
 
/// @ingroup userver_universal userver_containers
///
/// @brief Utility template for returning a pointer to an object that
/// is owned by someone else; throws std::runtime_error if nullptr is stored
///
/// Useful for returning cache search result.
template <typename T>
class CheckedPtr {
public:
    /* implicit */ constexpr CheckedPtr(std::nullptr_t) noexcept : ptr_{nullptr} {}
    explicit constexpr CheckedPtr(T* ptr) noexcept : ptr_{ptr} {}
 
    explicit constexpr operator bool() const noexcept {
#ifndef NDEBUG
        checked_ = true;
#endif
        return ptr_;
    }
 
    T* Get() const& {
        CheckPointer();
        return ptr_;
    }
 
    T* Get() && { RvalueDisabled(); }
 
    T* operator->() const& { return Get(); }
    T* operator->() && { RvalueDisabled(); }
 
    T& operator*() const& { return *Get(); }
    T& operator*() && { RvalueDisabled(); }
 
private:
    [[noreturn]] void RvalueDisabled() {
        static_assert(!sizeof(T), "Don't use temporary CheckedPtr, check it first, then dereference");
        std::abort();
    }
    void CheckPointer() const {
#ifndef NDEBUG
        UASSERT_MSG(checked_, "CheckedPtr contents were not checked before dereferencing");
#endif
        if (!ptr_) throw std::runtime_error{"Empty checked_pointer"};
    }
#ifndef NDEBUG
    mutable bool checked_{false};
#endif
    T* ptr_;
};
 
template <typename T>
class CheckedPtr<T&> {
    static_assert(!sizeof(T), "Don't use CheckedPointer for references");
};
 
template <typename T>
constexpr CheckedPtr<T> MakeCheckedPtr(T* ptr) noexcept {
    return CheckedPtr<T>{ptr};
}
 
}  // namespace utils
 
USERVER_NAMESPACE_END