Databases
StackOverflow2013
Postsdbo
POC++0x perfect forwarding getting in the way of copy ctor?
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POC++0x perfect forwarding getting in the way of copy ctor?
    primarykey
    data
    text
    <p>Using MSVC2010...</p> <p>I have a struct that wraps a std::string, with standard move ctor's defined, as well as a perfect forwarding ctor to forward an argument to the std::string ctor.</p> <pre><code>struct Wrapper { std::string value; Wrapper() { } Wrapper( Wrapper const&amp; rhs ) :value(rhs.value) { } Wrapper( Wrapper&amp;&amp; rhs ) :value(std::move(rhs.value)) { } Wrapper&amp; operator=( Wrapper const&amp; rhs ) { value = rhs.value; return *this; } Wrapper&amp; operator=( Wrapper&amp;&amp; rhs ) { value = std::move(rhs.value); return *this; } template&lt;typename StringT&gt; Wrapper( StringT&amp;&amp; value ) :value(std::forward&lt;StringT&gt;(value)) { } }; </code></pre> <p>However now it seems I cannot copy-construct a Wrapper from another wrapper</p> <pre><code>Wrapper w0; Wrapper w1(w0); </code></pre> <p>This results in a compile error pointing at the perfect forwarding ctor, saying it cannot convert a Wrapper to a std::string. Is this correct behavior? Shouldn't the compiler call the copy ctor, versus the templated overload?</p> <pre><code>1&gt;t:\depot\warp\code\apps\pf_test\main.cpp(56): error C2664: 'std::basic_string&lt;_Elem,_Traits,_Ax&gt;::basic_string(const std::basic_string&lt;_Elem,_Traits,_Ax&gt; &amp;)' : cannot convert parameter 1 from 'Wrapper' to 'const std::basic_string&lt;_Elem,_Traits,_Ax&gt; &amp;' 1&gt; with 1&gt; [ 1&gt; _Elem=char, 1&gt; _Traits=std::char_traits&lt;char&gt;, 1&gt; _Ax=std::allocator&lt;char&gt; 1&gt; ] 1&gt; Reason: cannot convert from 'Wrapper' to 'const std::basic_string&lt;_Elem,_Traits,_Ax&gt;' 1&gt; with 1&gt; [ 1&gt; _Elem=char, 1&gt; _Traits=std::char_traits&lt;char&gt;, 1&gt; _Ax=std::allocator&lt;char&gt; 1&gt; ] 1&gt; No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called 1&gt; t:\depot\warp\code\apps\pf_test\main.cpp(63) : see reference to function template instantiation 'Wrapper::Wrapper&lt;Wrapper&amp;&gt;(StringT)' being compiled 1&gt; with 1&gt; [ 1&gt; StringT=Wrapper &amp; 1&gt; ] 1&gt; </code></pre> <p>If I define another copy ctor, one that takes a non-const reference to Wrapper (shown below), then everything seems fine... Is this the way moving forward? Or did I mess something up? Or is this a bug in VS2010?</p> <pre><code> Wrapper( Wrapper&amp; rhs ) :value(rhs.value) { } </code></pre>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. This table or related slice is empty.
    1. USMikeNicolella
    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. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POC++0x perfect forwarding getting in the way of copy ctor?
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POC++0x perfect forwarding getting in the way of copy ctor?
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. POC++0x perfect forwarding getting in the way of copy ctor?
      1. This table or related slice is empty.
      1. VTUpMod
    1. COJust so you know, you don't need to hand write all of those constructors. They've added the ability to use 'Wrapper() = default;' syntax. It'll give you the default constructors and assignment operators (you'll need to do that for each ctr/op you want).
      singulars
      1. POC++0x perfect forwarding getting in the way of copy ctor?
      1. USJason Iverson
    2. COThanks for the tip - it seems VC2010 doesn't support this yet
      singulars
      1. POC++0x perfect forwarding getting in the way of copy ctor?
      1. USMikeNicolella
    3. COSorry, I forget sometimes since I primarily use gcc.
      singulars
      1. POC++0x perfect forwarding getting in the way of copy ctor?
      1. USJason Iverson
 

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