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Document refcount-saving hack

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Steven Dee (Jōshin) 2024-09-17 13:38:43 -07:00
parent e409c773e0
commit 1122f6a9d0
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1 changed files with 6 additions and 1 deletions
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7
ctl/shared_ptr.h
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@ -536,9 +536,14 @@ template<typename T, typename... Args>
shared_ptr<T>
make_shared(Args&&... args)
{
auto rc = __::shared_emplace<T>::make();
unique_ptr rc = __::shared_emplace<T>::make();
if constexpr (is_base_of_v<weak_self_base, T> &&
is_constructible_v<T, const weak_ptr<T>&, Args...>) {
// A __::shared_ref has a virtual weak reference that is owned by all of
// the shared references. We can avoid some unnecessary refcount changes
// by "borrowing" that reference and passing it to the constructor, then
// promoting it to a shared reference by swapping it with the shared_ptr
// that we return.
weak_ptr<T> w;
w.p = &rc->t;
w.rc = rc.get();