Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p><strong>Edit:</strong> This answer is wrong, even though, strictly speaking, the code works. I'm only leaving it here because the discussion under it is too useful. This other answer is the best answer given at the time I last edited this: <a href="https://stackoverflow.com/questions/8114276/how-passing-a-unique-ptr-as-argument-of-a-constructor-or-a-method/8114339#8114339">How do I pass a unique_ptr argument to a constructor or a function?</a></p> <p>The basic idea of <code>::std::move</code> is that people who are passing you the <code>unique_ptr</code> should be using it to express the knowledge that they know the <code>unique_ptr</code> they're passing in will lose ownership.</p> <p>This means you should be using an rvalue reference to a <code>unique_ptr</code> in your methods, not a <code>unique_ptr</code> itself. This won't work anyway because passing in a plain old <code>unique_ptr</code> would require making a copy, and that's explicitly forbidden in the interface for <code>unique_ptr</code>. Interestingly enough, using a named rvalue reference turns it back into an lvalue again, so you need to use <code>::std::move</code> <strong>inside</strong> your methods as well.</p> <p>This means your two methods should look like this:</p> <pre><code>Base(Base::UPtr &amp;&amp;n) : next(::std::move(n)) {} // Spaces for readability void setNext(Base::UPtr &amp;&amp;n) { next = ::std::move(n); } </code></pre> <p>Then people using the methods would do this:</p> <pre><code>Base::UPtr objptr{ new Base; } Base::UPtr objptr2{ new Base; } Base fred(::std::move(objptr)); // objptr now loses ownership fred.setNext(::std::move(objptr2)); // objptr2 now loses ownership </code></pre> <p>As you see, the <code>::std::move</code> expresses that the pointer is going to lose ownership at the point where it's most relevant and helpful to know. If this happened invisibly, it would be very confusing for people using your class to have <code>objptr</code> suddenly lose ownership for no readily apparent reason.</p>
    singulars
    1. This table or related slice is empty.
    1. POHow do I pass a unique_ptr argument to a constructor or a function?
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USCommunity
    1. USOmnifarious
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. CONamed rvalue references are lvalues.
      singulars
      1. PO
      1. USR. Martinho Fernandes
    2. COare you sure it's `Base fred(::std::move(objptr));` and not `Base::UPtr fred(::std::move(objptr));` ?
      singulars
      1. PO
      1. UScodablank1
    3. COTo add to my previous comment: this code won't compile. You still need to use `std::move` in the implementation of both the constructor and the method. And even when you pass by value, the caller must still use `std::move` to pass lvalues. The main difference being that with pass-by-value that interface makes it clear ownership will be lost. See Nicol Bolas comment on another answer.
      singulars
      1. PO
      1. USR. Martinho Fernandes
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload