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<title>Issue 339: definition of bitmask type restricted to clause 27</title>
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<p><em>This page is a snapshot from the LWG issues list, see the <a href="lwg-active.html">Library Active Issues List</a> for more information and the meaning of <a href="lwg-active.html#CD1">CD1</a> status.</em></p>
<h3 id="339"><a href="lwg-defects.html#339">339</a>. definition of bitmask type restricted to clause 27</h3>
<p><b>Section:</b> 28.3.4.2 <a href="https://wg21.link/category.ctype">[category.ctype]</a>, 16.3.3.3.3 <a href="https://wg21.link/bitmask.types">[bitmask.types]</a> <b>Status:</b> <a href="lwg-active.html#CD1">CD1</a>
 <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2001-09-17 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#category.ctype">issues</a> in [category.ctype].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#CD1">CD1</a> status.</p>
<p><b>Discussion:</b></p>
<p>
The ctype_category::mask type is declared to be an enum in 28.3.4.2 <a href="https://wg21.link/category.ctype">[category.ctype]</a> with p1 then stating that it is a bitmask type, most
likely referring to the definition of bitmask type in 16.3.3.3.3 <a href="https://wg21.link/bitmask.types">[bitmask.types]</a>, p1. However, the said definition only applies to
clause 27, making the reference in 22.2.1 somewhat dubious.
</p>


<p id="res-339"><b>Proposed resolution:</b></p>
<p>Clarify 17.3.2.1.2, p1 by changing the current text from</p>
    <blockquote><p>
    Several types defined in clause 27 are bitmask types. Each bitmask type
    can be implemented as an enumerated type that overloads certain operators,
    as an integer type, or as a bitset (22.9.2 <a href="https://wg21.link/template.bitset">[template.bitset]</a>).
    </p></blockquote>
<p>to read</p>
    <blockquote><p>
    Several types defined in clauses lib.language.support through 
    lib.input.output and Annex D are bitmask types. Each bitmask type can
    be implemented as an enumerated type that overloads certain operators,
    as an integer  type, or as a bitset (lib.template.bitset).
    </p></blockquote>

<p>
Additionally, change the definition in 22.2.1 to adopt the same
convention as in clause 27 by replacing the existing text with the
following (note, in particluar, the cross-reference to 17.3.2.1.2 in
22.2.1, p1):
</p>

<blockquote>
<p>22.2.1 The ctype category [lib.category.ctype]</p>
<pre>
namespace std {
    class ctype_base {
    public:
        typedef <b><i>T</i></b> mask;

        // numeric values are for exposition only.
        static const mask space = 1 &lt;&lt; 0;
        static const mask print = 1 &lt;&lt; 1;
        static const mask cntrl = 1 &lt;&lt; 2;
        static const mask upper = 1 &lt;&lt; 3;
        static const mask lower = 1 &lt;&lt; 4;
        static const mask alpha = 1 &lt;&lt; 5;
        static const mask digit = 1 &lt;&lt; 6;
        static const mask punct = 1 &lt;&lt; 7;
        static const mask xdigit = 1 &lt;&lt; 8;
        static const mask alnum = alpha | digit;
        static const mask graph = alnum | punct;
    };
}
</pre>

<p>The type <code>mask</code> is a bitmask type (16.3.3.3.3 <a href="https://wg21.link/bitmask.types">[bitmask.types]</a>).</p>
</blockquote>

<p><i>[Cura&ccedil;ao: The LWG notes that T above should be bold-italics to be
consistent with the rest of the standard.]</i></p>









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