R.21: Prefer unique_ptr over shared_ptr unless you need to share ownership
R.21:不需要共享所有權時應該使用unique_ptr而不是shared_ptr
Reason(原因)
A unique_ptr is conceptually simpler and more predictable (you know when destruction happens) and faster (you don't implicitly maintain a use count).
unique_ptr從概念上更簡單,動作更加可預見(你知道析構動作什麼時候發生)而且更快(不需要隱式維護使用計數)。
Example, bad(反面示例)
This needlessly adds and maintains a reference count.
不必要地增加和維護參照計數。
void f()
{
shared_ptr<Base> base = make_shared<Derived>();
// use base locally, without copying it -- refcount never exceeds 1
} // destroy base
Example(示例)
This is more efficient:
下面的代碼更高效:
void f()
{
unique_ptr<Base> base = make_unique<Derived>();
// use base locally
} // destroy base
Enforcement(實施建議)
(Simple) Warn if a function uses a Shared_pointer with an object allocated within the function, but never returns the Shared_pointer or passes it to a function requiring a Shared_pointer&. Suggest using unique_ptr instead.
(簡單)如果函數使用shared_ptr管理其內局部分配的對象,但是從來沒有返回該智能指針或者將其傳遞個一個需要shared_ptr&的函數,發出警告。建議使用unique_ptr。
原文鏈接
https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#r21-prefer-unique_ptr-over-shared_ptr-unless-you-need-to-share-ownership
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