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<title>Issue 1373: Customizable traits should have their own headers</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#NAD">NAD</a> status.</em></p>
<h3 id="1373"><a href="lwg-closed.html#1373">1373</a>. Customizable traits should have their own headers</h3>
<p><b>Section:</b> 22.2 <a href="https://wg21.link/utility">[utility]</a> <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a>
 <b>Submitter:</b> BSI <b>Opened:</b> 2010-08-25 <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#utility">issues</a> in [utility].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p>
<p><b>Discussion:</b></p>
<p><b>Addresses GB-79</b></p>
<p>
The library provides several traits mechanisms intended a
customization points for users. Typically, they are
declared in headers that are growing quite large. This is
not a problem for standard library vendors, who can
manage their internal file structure to avoid large
dependencies, but can be a problem for end users who
have no option but to include these large headers.
</p>

<p><i>[
2010 Rapperswil
]</i></p>

<p>
There was no enthusiasm for touching <code>char_traits</code> or <code>regex_traits</code>.
Consensus to move <code>iterator_traits</code>, <code>allocator_traits</code>
and <code>pointer_traits</code> to their own respective headers once wording supplied.
</p>

<p><i>[
2010 Rapperswil
]</i></p>

<p>
After some discussion, consensus is that moving these features into separate
headers does not buy much in practice, as the larger headers will inevitably
be included anyway.  Resolve as NAD.
</p>

<p><i>[
Resolution proposed in ballot comment
]</i></p>

<p>
Move the following traits classes into their own
headers, and require the existing header to
<code>#include</code> the traits header to support backwards
compatibility:
</p>
<blockquote><pre>
iterator_traits (plus the iterator tag-types)
allocator_traits
pointer_traits
char_traits
regex_traits
</pre></blockquote>

<p><i>[
2010 Batavia:
]</i></p>

<p>
Closed as NAD with the rationale below.
</p>



<p><b>Rationale:</b></p><p>
This suggest is not a defect, as the likely benefit is small, if any,
compared to the cost of not just implementating the feature, but also
explaining/teaching it.
</p>

<p id="res-1373"><b>Proposed resolution:</b></p>





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