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  <title>nuple: a Named Tuple - Alexandr Poltavsky, software developer</title>

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<h2>nuple: a Named Tuple</h2>

<p>While browsing the Internets I came upon this <a href="http://vitiy.info/named-tuple-for-cplusplus/" title="Named tuple for C++">blog post</a> by <a href="http://twitter.com/VictorLaskin" title="Victor Laskin Twitter">Victor Laskin</a>.
  In there he describes an implementation of a named tuple in C++. It just so happened that some
  time ago I was writing about useful properties of string interning in C++. I quickly realized
  that another good use of it is to implement a named tuple which I called <strong>nuple</strong> - a named
  tuple. By the way, you should check up Victor's <a href="http://vitiy.info/" title="Victor Laskin's Blog">blog</a> if you're a fan of functional
  programming and C++.</p>

<p>So, the implementation turned out to be pretty simple. The usage is like this:</p>

<pre><code>using nameid_t = nuple&lt; $("name"), char const*, $("id"), int &gt;;
</code></pre>

<p>The dollar sign is <a href="intern.html" title="Useful Properties of String Interning in C++">string interning</a> which turns a string literal into a type. All we
  have to do is to sort this parameter type list into a names list and a type list. The type list
  is then passed to <a href="https://github.com/alexpolt/luple/">luple</a> which is a lightweight (source code I mean) tuple I created for
  the <a href="type-loophole.html" title="The C++ Type Loophole (C++14)">C++ type loophole</a>. The <a href="https://github.com/alexpolt/luple/">source code</a> (GitHub) is short and easy to read
  (header is <strong>nuple.h</strong>).</p>

<p>So, here's an example of using it:</p>

<pre><code>nameid_t n[] = { {"alex", 1}, {"ivan", 2} };

for( auto&amp; v : n )
  printf( "name: %s, id: %d\n", get&lt;$("name")&gt;(v), get&lt;$("id")&gt;(v) );
</code></pre>

<p>Because <strong>nuple</strong> inherits from <strong>luple</strong> (I'm not good at terminology) we can use all other
  tuple-like methods:</p>

<pre><code>auto get_person(int i) { return nameid_t{"john", i}; }

auto p = get_person(3);

printf( "tuple size: %d\n", size(p) );

get&lt;0&gt;(p) = "irene";

get&lt;int&gt;(p) = 4;

printf( "name: %s, id: %d\n", get&lt;$("name")&gt;(p), get&lt;$("id")&gt;(p) );
</code></pre>

<p>See it in action <a href="https://goo.gl/zvo26z" title="luple Online Example at tio.run">online at tio.run</a> (also <a href="http://coliru.stacked-crooked.com/a/52984bf7d0b4db19" title="luple Online Example at Coliru">Coliru</a> or <a href="https://wandbox.org/permlink/ghbTSf5LwztoyCta" title="luple Online Example at Wandbox">Wandbox</a>).</p>

<p>Also a nuple-to-json <a href="https://goo.gl/c8ofW5" title="luple Online Example at tio.run">example at tio.run</a> (also <a href="http://coliru.stacked-crooked.com/a/8f2f84adae0cb751" title="luple Online Example at Coliru">Coliru</a> or <a href="https://wandbox.org/permlink/NBHrlq8UJ9kDf0KS" title="luple Online Example at Wandbox">Wandbox</a>).</p>

<p>There is no hacks. It's all valid C++ <a href="https://github.com/alexpolt/luple/">source code</a> (C++14) and can be safely used in
  production code. There is a limit on string length of 10 characters (sort of arbitrary), you can
  increase it by editing the $(...) macro in the intern.h header. Or #define N3599 to use the
  <a href="http://open-std.org/JTC1/SC22/WG21/docs/papers/2013/n3599.html" title="Literal operator templates for strings">N3599</a> proposal (adds string literal template to the language) which GCC and Clang implement
  as an extension. (Update: defined by default for GCC and Clang)</p>

<p><strong>Update</strong>. Added syntax like this:</p>

<pre><code>auto get_person( int id ) {

  return as_nuple( $name("name"), "Victoria", $name("id"), id );
}

auto p = get_person( 5 );

std::cout &lt;&lt; get&lt;$("name")&gt;( p );
</code></pre>

<p>Here macro $name(...) returns a value of an <a href="intern.html" title="Useful Properties of String Interning in C++">interned string</a> type ( $(...) gives a type ).</p>

<p>There is a Reddit <a href="https://www.reddit.com/r/cpp/comments/75wc6j/nuple_a_named_tuple/" title="nuple: a Named Tuple on Reddit">discussion</a>. Follow me on <a href="https://twitter.com/poltavsky_alex" title="Alexandr Poltavsky, Software Developer">Twitter</a> for updates about my new
  articles (mostly programming and computer graphics). </p>

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