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    <blockquote> <p>is there some other clause in the language specification that this exploits?</p> </blockquote> <p>Yes, see 12.8 §34 and §35:</p> <blockquote> <p>When certain criteria are met, an implementation is allowed to omit the copy/move construction of a class object [...] This elision of copy/move operations, called <em>copy elision</em>, is permitted [...] in a return statement in a function with a class return type, <strong>when the expression is the name of a non-volatile automatic object</strong> with the same cv-unqualified type as the function return type [...]</p> <p>When the criteria for elision of a copy operation are met and the object to be copied is designated by an lvalue, overload resolution to select the constructor for the copy is first performed <strong>as if the object were designated by an rvalue</strong>.</p> </blockquote> <hr> <p>Just wanted to add one more point that returning by value should be the default choice here because a named value in the return statement in the worst case, i.e. without elisions in C++11, C++14 and C++17 is treated as an rvalue. So for example the following function compiles with the <code>-fno-elide-constructors</code> flag</p> <pre><code>std::unique_ptr&lt;int&gt; get_unique() { auto ptr = std::unique_ptr&lt;int&gt;{new int{2}}; // &lt;- 1 return ptr; // &lt;- 2, moved into the to be returned unique_ptr } ... auto int_uptr = get_unique(); // &lt;- 3 </code></pre> <p>With the flag set on compilation there are two moves (1 and 2) happening in this function and then one move later on (3). </p>
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    1. COheh, was about to post a guess saying the same thing but I didn't have the new standard in front of me.
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    2. CO@juanchopanza Do you essentially mean that `foo()` is indeed also about to be destroyed (if it were not assigned to anything), just like the return value within the function, and hence it makes sense that C++ uses a move constructor when doing `unique_ptr<int> p = foo();`?
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