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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
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<title>Pending Issues</title>
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<meta name="generator" content="DocBook XSL Stylesheets V1.79.1">
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<link rel="home" href="index.html" title="Safe Numerics">
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<link rel="up" href="index.html" title="Safe Numerics">
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<link rel="prev" href="rationale.html" title="Rationale and FAQ">
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<link rel="next" href="acknowledgements.html" title="Acknowledgements">
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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
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<td valign="top"><img href="index.html" height="164px" src="pre-boost.jpg" alt="Library Documentation Index"></td>
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<td><h2>Safe Numerics</h2></td>
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<div class="spirit-nav">
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<a accesskey="p" href="rationale.html"><img src="images/prev.png" alt="Prev"></a><a accesskey="u" href="index.html"><img src="images/up.png" alt="Up"></a><a accesskey="h" href="index.html"><img src="images/home.png" alt="Home"></a><a accesskey="n" href="acknowledgements.html"><img src="images/next.png" alt="Next"></a>
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</div>
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<div class="section">
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
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<a name="safe_numerics.pending_issues"></a>Pending Issues</h2></div></div></div>
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<div class="toc"><dl class="toc">
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<dt><span class="section"><a href="pending_issues.html#idm462682896128"><code class="computeroutput">safe_base</code> Only Works for Scalar Types</a></span></dt>
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<dt><span class="section"><a href="pending_issues.html#idm462682856528">Other Pending Issues</a></span></dt>
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</dl></div>
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<p>The library is under development. There are a number of issues still
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pending.</p>
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<div class="section">
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<div class="titlepage"><div><div><h3 class="title">
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<a name="idm462682896128"></a><code class="computeroutput">safe_base</code> Only Works for Scalar Types</h3></div></div></div>
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<p>The following is paraphrased from an issue raised by Andrzej
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Krzemieński as a <a href="https://github.com/robertramey/safe_numerics/issues/44" target="_top">github
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issue</a>. It touches upon fundamental ideas behind the library and
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how these ideas as the implementation of the library collided with
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reality.</p>
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<p><span class="quote">“<span class="quote">In the current implementation safe<T> will only work
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with T being a C++ scalar type. Therefore making a general type
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requirements that say what operations are allowed is superfluous, and
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confusing (because it implies that safe<> is more
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generic.</span>”</span></p>
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<p>When I started out, It became clear that I wanted "safe" types to
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look like "numeric" types. It also became clear pretty soon that there was
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going to be significant template meta-programming in the implementation.
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Normal type traits like std::is_integer are defined in the std namespace
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and one is discouraged from extending it. Also I needed some compile time
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"max" and "lowest" values. This lead me to base the design on
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std::numeric_limits. But std::numeric limits is inherently extensible to
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any "numeric" type. For example, money is a numeric type but not an
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intrinsic types. So it seemed that I needed to define a "numeric" concept
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which required that there be an implementation of std::numeric_limits for
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any type T - such as money in this case. When I'm doubt - I tend to think
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big.</p>
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<p>For now though I'm not going to address it. For what it's worth, my
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preference would be to do something like: </p>
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<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">></span>
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<span class="keyword">struct</span> <span class="identifier">range</span> <span class="special">{</span>
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<span class="identifier">T</span> <span class="identifier">m_lowest</span><span class="special">;</span>
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<span class="identifier">T</span> <span class="identifier">m_highest</span><span class="special">;</span>
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<span class="comment">// default implementation</span>
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<span class="identifier">range</span><span class="special">(</span>
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<span class="keyword">const</span> <span class="special">&</span> <span class="identifier">T</span> <span class="identifier">t_min</span><span class="special">,</span>
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<span class="keyword">const</span> <span class="special">&</span> <span class="identifier">T</span> <span class="identifier">t_max</span>
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<span class="special">)</span> <span class="special">:</span>
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<span class="identifier">m_lowest</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span><span class="special">::</span><span class="identifier">lowest</span><span class="special">(</span><span class="identifier">t_min</span><span class="special">)</span><span class="special">,</span>
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<span class="identifier">m_highest</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span><span class="special">::</span><span class="identifier">max</span><span class="special">(</span><span class="identifier">t_max</span><span class="special">)</span>
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<span class="special">{</span><span class="special">}</span>
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<span class="special">}</span><span class="special">;</span></pre>
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<p>Then redeclare <code class="computeroutput">safe_base</code>, etc., accordingly.</p>
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<p>Also note that for C++20, template value parameters are no longer
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restricted to integer primitive types but may be class types as well. This
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means the library maybe extended to user class types without changing the
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current template signatures.</p>
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</div>
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<div class="section">
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<div class="titlepage"><div><div><h3 class="title">
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<a name="idm462682856528"></a>Other Pending Issues</h3></div></div></div>
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<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
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<li class="listitem"><p>The library is currently limited to integers. If there is
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interest, it could be extended to floats and possible to user
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defined types.</p></li>
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<li class="listitem"><p>Although care has been taken to make the library portable, at
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least some parts of the implementation - particularly
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<code class="computeroutput">checked</code> integer arithmetic - depend upon two's
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complement representation of integers. Hence the library is probably
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not currently portable to all other possible C++ architectures.
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These days, this is unlikely to be a limitation in practice.
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Starting with C++20, integer arithmetic will be guaranteed by the
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C++ standard to be two's complement.</p></li>
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<li class="listitem"><p><code class="computeroutput">std::common_type</code> is used in a variety of generic
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libraries, including std::chrono. Without a specialization for
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<code class="computeroutput">safe<T></code>s one cannot use the safe wrappers e.g. as
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a representation for <code class="computeroutput">std::chrono::duration</code>.</p></li>
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</ul></div>
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</div>
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</div>
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<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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<td align="left"></td>
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<td align="right"><div class="copyright-footer">Copyright © 2012-2018 Robert Ramey<p><a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">Subject to Boost
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Software License</a></p>
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</div></td>
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</tr></table>
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<hr>
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<a accesskey="p" href="rationale.html"><img src="images/prev.png" alt="Prev"></a><a accesskey="u" href="index.html"><img src="images/up.png" alt="Up"></a><a accesskey="h" href="index.html"><img src="images/home.png" alt="Home"></a><a accesskey="n" href="acknowledgements.html"><img src="images/next.png" alt="Next"></a>
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