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POMove semantics & returning const values
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  1. POMove semantics & returning const values
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    copied!<p>I have the habit (?!?!?) of returning everything as a "const" value. Like this...</p> <pre><code>struct s; s const make_s(); s const &amp;s0 = make_s(); s const s1 = make_s(); </code></pre> <p>With move operations and r-value references and the following functions...</p> <pre><code>void take_s(s &amp;&amp;s0); void take_s(s const &amp;&amp;s0); // Doesn't make sense </code></pre> <p>I can no longer write...</p> <pre><code>take_s(make_s()); </code></pre> <p>The main reason I started using the convention of returning const values is to prevent someone from writing code like this...</p> <pre><code>make_s().mutating_member_function(); </code></pre> <p>The use case is the following...</p> <pre><code>struct c_str_proxy { std::string m_s; c_str_proxy(std::string &amp;&amp;s) : m_s(std::move(s)) { } }; c_str_proxy c_str(std::string &amp;&amp;s) { return c_str_proxy(s); } char const * const c_str(std::string const &amp;s) { return s.c_str(); } std::vector &lt; std::string &gt; const &amp;v = make_v(); std::puts(c_str(boost::join(v, ", "))); std::string const my_join(std::vector &lt; std::string &gt; const &amp;v, char const *sep); // THE FOLLOWING WORKS, BUT I THINK THAT IS ACCIDENTAL // IT CALLS // // c_str(std::string const &amp;); // // BUT I THINK THE TEMPORARY RETURNED BY // // my_join(v, "; ") // // IS NO LONGER ALIVE BY THE TIME WE ARE INSIDE // // std::puts // // AS WE ARE TAKING THE "c_str()" OF A TEMPORARY "std::string" // std::puts(c_str(my_join(v, "; "))); </code></pre> <p>Looks as if "returning const value" and r-value references don't mix in this particular use case. Is that right?</p> <pre><code>**Edit 0: Extra question...** </code></pre> <p>The object is temporary anyway. Why should "const" prevent moving? Why can't we move "const" temporaries?</p>
 

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