Comments on: Rvalue reference pitfalls, an update https://codesynthesis.com/~boris/blog//2012/03/14/rvalue-reference-pitfalls-update/ Boris Kolpackov's blog about software Wed, 29 Apr 2026 18:48:50 +0000 http://wordpress.org/?v=2.2.2 By: JJ https://codesynthesis.com/~boris/blog//2012/03/14/rvalue-reference-pitfalls-update/#comment-1923 JJ Thu, 15 Mar 2012 10:24:19 +0000 https://codesynthesis.com/~boris/blog//2012/03/14/rvalue-reference-pitfalls-update/#comment-1923 got it. quite tricky indeed. Thx for your answer! got it. quite tricky indeed. Thx for your answer!

]]> By: Boris Kolpackov https://codesynthesis.com/~boris/blog//2012/03/14/rvalue-reference-pitfalls-update/#comment-1922 Boris Kolpackov Thu, 15 Mar 2012 09:21:57 +0000 https://codesynthesis.com/~boris/blog//2012/03/14/rvalue-reference-pitfalls-update/#comment-1922 JJ, someone asked this question in the reddit's discussion of this post: http://www.reddit.com/r/cpp/comments/qw786/rvalue_reference_pitfalls_an_update/ I have also provided an answer there. JJ, someone asked this question in the reddit’s discussion of this post:

http://www.reddit.com/r/cpp/comments/qw786/rvalue_reference_pitfalls_an_update/

I have also provided an answer there.

]]> By: Boris Kolpackov https://codesynthesis.com/~boris/blog//2012/03/14/rvalue-reference-pitfalls-update/#comment-1921 Boris Kolpackov Thu, 15 Mar 2012 09:19:27 +0000 https://codesynthesis.com/~boris/blog//2012/03/14/rvalue-reference-pitfalls-update/#comment-1921 Anonymous, no, in this case the second constructor will be selected since its second argument becomes an lvalue reference. Anonymous, no, in this case the second constructor will be selected since its second argument becomes an lvalue reference.

]]> By: JJ https://codesynthesis.com/~boris/blog//2012/03/14/rvalue-reference-pitfalls-update/#comment-1920 JJ Thu, 15 Mar 2012 09:03:33 +0000 https://codesynthesis.com/~boris/blog//2012/03/14/rvalue-reference-pitfalls-update/#comment-1920 As for this: "If you are wondering why this is a problem (after all, the first two constructors accomplish essentially the same), consider that while the first constructor’s hypothetical implementation will use a copy constructor to initialize the id, the second constructor will most likely use the move constructor to accomplish the same." Then, how about having only the second, perfect-forwarding one, and in it using std::forward() instead of std::move()? Wouldn't this solve the issue better than your solution involving enable_if? As for this: “If you are wondering why this is a problem (after all, the first two constructors accomplish essentially the same), consider that while the first constructor’s hypothetical implementation will use a copy constructor to initialize the id, the second constructor will most likely use the move constructor to accomplish the same.”

Then, how about having only the second, perfect-forwarding one, and in it using std::forward() instead of std::move()? Wouldn’t this solve the issue better than your solution involving enable_if?

]]> By: Anonymous https://codesynthesis.com/~boris/blog//2012/03/14/rvalue-reference-pitfalls-update/#comment-1919 Anonymous Thu, 15 Mar 2012 08:13:16 +0000 https://codesynthesis.com/~boris/blog//2012/03/14/rvalue-reference-pitfalls-update/#comment-1919 I have a feeling you meant 'fourth' instead of 'second' here where you refer to the constructor selected. "Instead of selecting the third constructor, the overload resolution rules select the second because the rvalue reference in its second argument becomes an lvalue reference (see the original post for details on why this happens)." I have a feeling you meant ‘fourth’ instead of ’second’ here where you refer to the constructor selected.

“Instead of selecting the third constructor, the overload resolution rules select the second because the rvalue reference in its second argument becomes an lvalue reference (see the original post for details on why this happens).”

]]> By: Boris Kolpackov https://codesynthesis.com/~boris/blog//2012/03/14/rvalue-reference-pitfalls-update/#comment-1917 Boris Kolpackov Wed, 14 Mar 2012 18:07:36 +0000 https://codesynthesis.com/~boris/blog//2012/03/14/rvalue-reference-pitfalls-update/#comment-1917 Yes, that was a type. Fixed, thanks! Yes, that was a type. Fixed, thanks!

]]> By: haohaolee https://codesynthesis.com/~boris/blog//2012/03/14/rvalue-reference-pitfalls-update/#comment-1916 haohaolee Wed, 14 Mar 2012 15:47:23 +0000 https://codesynthesis.com/~boris/blog//2012/03/14/rvalue-reference-pitfalls-update/#comment-1916 don't know if this is a typo when you say take its argument by value: ... template lazy_shared_ptr (database&, std::shared_ptr& p) : p_ (std::move (p)) don’t know if this is a typo when you say take its argument by value:
…
template
lazy_shared_ptr (database&, std::shared_ptr& p)
: p_ (std::move (p))

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