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IntrusivePtr: replace the "add_ref" parameter with tag structs

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Using a runtime parameter is obscure and error-prone.  Avoiding
error-prone code and getting reference counting right is the whole
point of this class.
This commit is contained in:
Max Kellermann 2020-02-19 05:48:02 +01:00
parent 7c0863dccf
commit 31b3a56740
7 changed files with 41 additions and 15 deletions
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38
src/IntrusivePtr.h
View file

@ -5,6 +5,18 @@
#include <type_traits>
#include <utility>
/**
* A tag class for the #IntrusivePtr constructor which means: adopt
* the reference from the caller.
*/
struct AdoptRef {};
/**
* A tag class for the #IntrusivePtr constructor which means: create a
* new reference to the object.
*/
struct NewRef {};
/**
* An intrusive, reference counting smart pointer implementation. Much like
* @c std::shared_ptr, this smart pointer models shared ownership of an object
@ -54,13 +66,27 @@ public:
/**
* Constructs a new intrusive pointer for managing the lifetime of the object
* pointed to by @c raw_ptr.
*
* This overload adopts the existing reference from the caller.
*
* @param raw_ptr Pointer to the shared object.
* @param add_ref Denotes whether the reference count of the object shall be
* increased during construction.
*/
IntrusivePtr(pointer raw_ptr, bool add_ref) noexcept
IntrusivePtr(AdoptRef, pointer raw_ptr) noexcept
{
setPtr(raw_ptr, add_ref);
setPtr(raw_ptr, false);
}
/**
* Constructs a new intrusive pointer for managing the lifetime of the object
* pointed to by @c raw_ptr.
*
* This overload adds a new reference.
*
* @param raw_ptr Pointer to the shared object.
*/
IntrusivePtr(NewRef, pointer raw_ptr) noexcept
{
setPtr(raw_ptr, true);
}
IntrusivePtr(IntrusivePtr&& other) noexcept : ptr_(other.release())
@ -69,8 +95,8 @@ public:
}
IntrusivePtr(const IntrusivePtr& other) noexcept
: IntrusivePtr(NewRef{}, other.get())
{
setPtr(other.get(), true);
}
template <class U, class = std::enable_if_t<std::is_convertible_v<U*, T*>>>
@ -157,7 +183,7 @@ template <class T, class... Ts>
IntrusivePtr<T> make_intrusive(Ts&&... args)
{
// Assumes that objects start with a reference count of 1!
return {new T(std::forward<Ts>(args)...), false};
return {AdoptRef{}, new T(std::forward<Ts>(args)...)};
}
// -- comparison to nullptr ----------------------------------------------------