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<title>8.9 Overriding in open statements</title>
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<h2 class="section" id="s:explicit-overriding-open"><a class="section-anchor" href="#s:explicit-overriding-open" aria-hidden="true"></a>8.9 Overriding in open statements</h2>
<p>
<a id="hevea_manual.kwd224"></a>
</p><p>(Introduced in OCaml 4.01)</p><div class="syntax"><table class="display dcenter"><tr class="c019"><td class="dcell"><table class="c001 cellpading0"><tr><td class="c018">
<a class="syntax" href="modules.html#definition"><span class="c010">definition</span></a></td><td class="c015">::=</td><td class="c017">
...
</td></tr>
<tr><td class="c018"> </td><td class="c015">∣</td><td class="c017"> <span class="c004">open!</span> <a class="syntax" href="names.html#module-path"><span class="c010">module-path</span></a>
</td></tr>
<tr><td class="c018"> </td></tr>
<tr><td class="c018">
<a class="syntax" href="modtypes.html#specification"><span class="c010">specification</span></a></td><td class="c015">::=</td><td class="c017">
...
</td></tr>
<tr><td class="c018"> </td><td class="c015">∣</td><td class="c017"> <span class="c004">open!</span> <a class="syntax" href="names.html#module-path"><span class="c010">module-path</span></a>
</td></tr>
<tr><td class="c018"> </td></tr>
<tr><td class="c018">
<a class="syntax" href="expr.html#expr"><span class="c010">expr</span></a></td><td class="c015">::=</td><td class="c017">
...
</td></tr>
<tr><td class="c018"> </td><td class="c015">∣</td><td class="c017"> <span class="c004">let</span> <span class="c004">open!</span> <a class="syntax" href="names.html#module-path"><span class="c010">module-path</span></a> <span class="c004">in</span> <a class="syntax" href="expr.html#expr"><span class="c010">expr</span></a>
</td></tr>
<tr><td class="c018"> </td></tr>
<tr><td class="c018">
<span class="c010">class-body-type</span></td><td class="c015">::=</td><td class="c017">
...
</td></tr>
<tr><td class="c018"> </td><td class="c015">∣</td><td class="c017"> <span class="c004">let</span> <span class="c004">open!</span> <a class="syntax" href="names.html#module-path"><span class="c010">module-path</span></a> <span class="c004">in</span> <a class="syntax" href="classes.html#class-body-type"><span class="c010">class-body-type</span></a>
</td></tr>
<tr><td class="c018"> </td></tr>
<tr><td class="c018">
<span class="c010">class-expr</span></td><td class="c015">::=</td><td class="c017">
...
</td></tr>
<tr><td class="c018"> </td><td class="c015">∣</td><td class="c017"> <span class="c004">let</span> <span class="c004">open!</span> <a class="syntax" href="names.html#module-path"><span class="c010">module-path</span></a> <span class="c004">in</span> <a class="syntax" href="classes.html#class-expr"><span class="c010">class-expr</span></a>
</td></tr>
<tr><td class="c018"> </td></tr>
</table></td></tr>
</table></div><p>Since OCaml 4.01, <span class="c004">open</span> statements shadowing an existing identifier
(which is later used) trigger the warning 44. Adding a <span class="c004">!</span>
character after the <span class="c004">open</span> keyword indicates that such a shadowing is
intentional and should not trigger the warning.</p><p>This is also available (since OCaml 4.06) for local opens in class
expressions and class type expressions.</p>
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