<p dir="auto">There are at least three sets of URLs that give the same thing:</p>
<p dir="auto"><a href="http://doc.rust-lang.org/std/" rel="nofollow">http://doc.rust-lang.org/std/</a><br>
<a href="http://doc.rust-lang.org/nightly/std/" rel="nofollow">http://doc.rust-lang.org/nightly/std/</a><br>
<a href="http://static.rust-lang.org/doc/master/std/" rel="nofollow">http://static.rust-lang.org/doc/master/std/</a></p>
<p dir="auto">One of the should be picked and the others redirect to it.</p>
<p dir="auto">Related, but I believe not quite duplicate: <a class="issue-link js-issue-link" data-error-text="Failed to load title" data-id="19965114" data-permission-text="Title is private" data-url="https://github.com/rust-lang/rust/issues/9461" data-hovercard-type="issue" data-hovercard-url="/rust-lang/rust/issues/9461/hovercard" href="https://github.com/rust-lang/rust/issues/9461">#9461</a>, <a class="issue-link js-issue-link" data-error-text="Failed to load title" data-id="28092575" data-permission-text="Title is private" data-url="https://github.com/rust-lang/rust/issues/12466" data-hovercard-type="issue" data-hovercard-url="/rust-lang/rust/issues/12466/hovercard" href="https://github.com/rust-lang/rust/issues/12466">#12466</a>, <a class="issue-link js-issue-link" data-error-text="Failed to load title" data-id="34413342" data-permission-text="Title is private" data-url="https://github.com/rust-lang/rust/issues/14466" data-hovercard-type="issue" data-hovercard-url="/rust-lang/rust/issues/14466/hovercard" href="https://github.com/rust-lang/rust/issues/14466">#14466</a>, <a class="issue-link js-issue-link" data-error-text="Failed to load title" data-id="47554893" data-permission-text="Title is private" data-url="https://github.com/rust-lang/rust/issues/18558" data-hovercard-type="issue" data-hovercard-url="/rust-lang/rust/issues/18558/hovercard" href="https://github.com/rust-lang/rust/issues/18558">#18558</a>.</p>
<p dir="auto">CC <a class="user-mention notranslate" data-hovercard-type="user" data-hovercard-url="/users/brson/hovercard" data-octo-click="hovercard-link-click" data-octo-dimensions="link_type:self" href="https://github.com/brson">@brson</a></p>
<p dir="auto">The <code class="notranslate">Ref</code> type connected to <code class="notranslate">RefCell</code> supports some methods for changing the type of the reference, such as <code class="notranslate">map</code> and <code class="notranslate">filter_map</code>. While <code class="notranslate">map</code> is clearly fully general, <code class="notranslate">filter_map</code> is somewhat of a special case hooked into <code class="notranslate">Option</code>. To make it fully general would likely require HKT. We need an overall plan before stabilization.</p>