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<ol class="chapter"><li class="chapter-item expanded "><a href="../index.html"><strong aria-hidden="true">1.</strong> Rust ❤️ C++</a></li><li class="chapter-item expanded "><a href="../concepts.html"><strong aria-hidden="true">2.</strong> Core concepts</a></li><li class="chapter-item expanded "><a href="../tutorial.html"><strong aria-hidden="true">3.</strong> Tutorial</a></li><li class="chapter-item expanded "><a href="../context.html"><strong aria-hidden="true">4.</strong> Other Rust–C++ interop tools</a></li><li class="chapter-item expanded "><a href="../building.html"><strong aria-hidden="true">5.</strong> Multi-language build system options</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../build/cargo.html"><strong aria-hidden="true">5.1.</strong> Cargo</a></li><li class="chapter-item expanded "><a href="../build/bazel.html"><strong aria-hidden="true">5.2.</strong> Bazel or Buck2</a></li><li class="chapter-item expanded "><a href="../build/cmake.html"><strong aria-hidden="true">5.3.</strong> CMake</a></li><li class="chapter-item expanded "><a href="../build/other.html"><strong aria-hidden="true">5.4.</strong> More...</a></li></ol></li><li class="chapter-item expanded "><a href="../reference.html"><strong aria-hidden="true">6.</strong> Reference: the bridge module</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../extern-rust.html"><strong aria-hidden="true">6.1.</strong> extern "Rust"</a></li><li class="chapter-item expanded "><a href="../extern-c++.html"><strong aria-hidden="true">6.2.</strong> extern "C++"</a></li><li class="chapter-item expanded "><a href="../shared.html"><strong aria-hidden="true">6.3.</strong> Shared types</a></li><li class="chapter-item expanded "><a href="../attributes.html"><strong aria-hidden="true">6.4.</strong> Attributes</a></li><li class="chapter-item expanded "><a href="../async.html"><strong aria-hidden="true">6.5.</strong> Async functions</a></li><li class="chapter-item expanded "><a href="../binding/result.html"><strong aria-hidden="true">6.6.</strong> Error handling</a></li></ol></li><li class="chapter-item expanded "><a href="../bindings.html"><strong aria-hidden="true">7.</strong> Reference: built-in bindings</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../binding/string.html"><strong aria-hidden="true">7.1.</strong> String — rust::String</a></li><li class="chapter-item expanded "><a href="../binding/str.html"><strong aria-hidden="true">7.2.</strong> &str — rust::Str</a></li><li class="chapter-item expanded "><a href="../binding/slice.html" class="active"><strong aria-hidden="true">7.3.</strong> &[T], &mut [T] — rust::Slice&lt;T&gt;</a></li><li class="chapter-item expanded "><a href="../binding/cxxstring.html"><strong aria-hidden="true">7.4.</strong> CxxString — std::string</a></li><li class="chapter-item expanded "><a href="../binding/box.html"><strong aria-hidden="true">7.5.</strong> Box&lt;T&gt; — rust::Box&lt;T&gt;</a></li><li class="chapter-item expanded "><a href="../binding/uniqueptr.html"><strong aria-hidden="true">7.6.</strong> UniquePtr&lt;T&gt; — std::unique_ptr&lt;T&gt;</a></li><li class="chapter-item expanded "><a href="../binding/sharedptr.html"><strong aria-hidden="true">7.7.</strong> SharedPtr&lt;T&gt; — std::shared_ptr&lt;T&gt;</a></li><li class="chapter-item expanded "><a href="../binding/vec.html"><strong aria-hidden="true">7.8.</strong> Vec&lt;T&gt; — rust::Vec&lt;T&gt;</a></li><li class="chapter-item expanded "><a href="../binding/cxxvector.html"><strong aria-hidden="true">7.9.</strong> CxxVector&lt;T&gt; — std::vector&lt;T&gt;</a></li><li class="chapter-item expanded "><a href="../binding/rawptr.html"><strong aria-hidden="true">7.10.</strong> *mut T, *const T raw pointers</a></li><li class="chapter-item expanded "><a href="../binding/fn.html"><strong aria-hidden="true">7.11.</strong> Function pointers</a></li><li class="chapter-item expanded "><a href="../binding/result.html"><strong aria-hidden="true">7.12.</strong> Result&lt;T&gt;</a></li></ol></li><li class="part-title"><a href="https://github.com/dtolnay/cxx"><i class="fa fa-github"></i>https://github.com/dtolnay/cxx</a></li></ol>
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<h1 id="rustsliceconst-t-rustslicet"><a class="header" href="#rustsliceconst-t-rustslicet">rust::Slice&lt;const T&gt;, rust::Slice&lt;T&gt;</a></h1>
<ul>
<li>Rust <code class="hljs">&amp;[T]</code> is written <code class="hljs">rust::Slice&lt;const T&gt;</code> in C++</li>
<li>Rust <code class="hljs">&amp;mut [T]</code> is written <code class="hljs">rust::Slice&lt;T&gt;</code> in C++</li>
</ul>
<h3 id="public-api"><a class="header" href="#public-api">Public API:</a></h3>
<pre><code class="hidelines=... hidelines hide-boring hljs"><span class="hljs-comment">// rust/cxx.h</span>
<span class="boring">
</span><span class="boring"><span class="hljs-meta">#<span class="hljs-meta-keyword">include</span> <span class="hljs-meta-string">&lt;iterator&gt;</span></span>
</span><span class="boring"><span class="hljs-meta">#<span class="hljs-meta-keyword">include</span> <span class="hljs-meta-string">&lt;type_traits&gt;</span></span>
</span><span class="boring">
</span><span class="boring"><span class="hljs-keyword">namespace</span> rust {
</span>
<span class="hljs-keyword">template</span> &lt;<span class="hljs-keyword">typename</span> T&gt;
<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Slice</span> <span class="hljs-title">final</span> {</span>
<span class="hljs-keyword">public</span>:
<span class="hljs-keyword">using</span> value_type = T;
Slice() <span class="hljs-keyword">noexcept</span>;
Slice(<span class="hljs-keyword">const</span> Slice&lt;T&gt; &amp;) <span class="hljs-keyword">noexcept</span>;
Slice(T *, <span class="hljs-keyword">size_t</span> count) <span class="hljs-keyword">noexcept</span>;
Slice &amp;<span class="hljs-keyword">operator</span>=(Slice&lt;T&gt; &amp;&amp;) <span class="hljs-keyword">noexcept</span>;
Slice &amp;<span class="hljs-keyword">operator</span>=(<span class="hljs-keyword">const</span> Slice&lt;T&gt; &amp;) <span class="hljs-keyword">noexcept</span>
<span class="hljs-keyword">requires</span> <span class="hljs-built_in">std</span>::is_const_v&lt;T&gt;;
<span class="hljs-function">T *<span class="hljs-title">data</span><span class="hljs-params">()</span> <span class="hljs-keyword">const</span> <span class="hljs-keyword">noexcept</span></span>;
<span class="hljs-function"><span class="hljs-keyword">size_t</span> <span class="hljs-title">size</span><span class="hljs-params">()</span> <span class="hljs-keyword">const</span> <span class="hljs-keyword">noexcept</span></span>;
<span class="hljs-function"><span class="hljs-keyword">size_t</span> <span class="hljs-title">length</span><span class="hljs-params">()</span> <span class="hljs-keyword">const</span> <span class="hljs-keyword">noexcept</span></span>;
<span class="hljs-function"><span class="hljs-keyword">bool</span> <span class="hljs-title">empty</span><span class="hljs-params">()</span> <span class="hljs-keyword">const</span> <span class="hljs-keyword">noexcept</span></span>;
T &amp;<span class="hljs-keyword">operator</span>[](<span class="hljs-keyword">size_t</span> n) <span class="hljs-keyword">const</span> <span class="hljs-keyword">noexcept</span>;
<span class="hljs-function">T &amp;<span class="hljs-title">at</span><span class="hljs-params">(<span class="hljs-keyword">size_t</span> n)</span> <span class="hljs-keyword">const</span></span>;
<span class="hljs-function">T &amp;<span class="hljs-title">front</span><span class="hljs-params">()</span> <span class="hljs-keyword">const</span> <span class="hljs-keyword">noexcept</span></span>;
<span class="hljs-function">T &amp;<span class="hljs-title">back</span><span class="hljs-params">()</span> <span class="hljs-keyword">const</span> <span class="hljs-keyword">noexcept</span></span>;
<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">iterator</span>;</span>
<span class="hljs-function">iterator <span class="hljs-title">begin</span><span class="hljs-params">()</span> <span class="hljs-keyword">const</span> <span class="hljs-keyword">noexcept</span></span>;
<span class="hljs-function">iterator <span class="hljs-title">end</span><span class="hljs-params">()</span> <span class="hljs-keyword">const</span> <span class="hljs-keyword">noexcept</span></span>;
<span class="hljs-function"><span class="hljs-keyword">void</span> <span class="hljs-title">swap</span><span class="hljs-params">(Slice &amp;)</span> <span class="hljs-keyword">noexcept</span></span>;
};
<span class="boring">
</span><span class="boring"><span class="hljs-keyword">template</span> &lt;<span class="hljs-keyword">typename</span> T&gt;
</span><span class="boring"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Slice</span>&lt;T&gt;:</span>:iterator <span class="hljs-keyword">final</span> {
</span><span class="boring"><span class="hljs-keyword">public</span>:
</span><span class="boring"> <span class="hljs-keyword">using</span> iterator_category = <span class="hljs-built_in">std</span>::random_access_iterator_tag;
</span><span class="boring"> <span class="hljs-keyword">using</span> value_type = T;
</span><span class="boring"> <span class="hljs-keyword">using</span> pointer = T *;
</span><span class="boring"> <span class="hljs-keyword">using</span> reference = T &amp;;
</span><span class="boring">
</span><span class="boring"> T &amp;<span class="hljs-keyword">operator</span>*() <span class="hljs-keyword">const</span> <span class="hljs-keyword">noexcept</span>;
</span><span class="boring"> T *<span class="hljs-keyword">operator</span>-&gt;() <span class="hljs-keyword">const</span> <span class="hljs-keyword">noexcept</span>;
</span><span class="boring"> T &amp;<span class="hljs-keyword">operator</span>[](<span class="hljs-keyword">ptrdiff_t</span>) <span class="hljs-keyword">const</span> <span class="hljs-keyword">noexcept</span>;
</span><span class="boring">
</span><span class="boring"> iterator &amp;<span class="hljs-keyword">operator</span>++() <span class="hljs-keyword">noexcept</span>;
</span><span class="boring"> iterator <span class="hljs-keyword">operator</span>++(<span class="hljs-keyword">int</span>) <span class="hljs-keyword">noexcept</span>;
</span><span class="boring"> iterator &amp;<span class="hljs-keyword">operator</span>--() <span class="hljs-keyword">noexcept</span>;
</span><span class="boring"> iterator <span class="hljs-keyword">operator</span>--(<span class="hljs-keyword">int</span>) <span class="hljs-keyword">noexcept</span>;
</span><span class="boring">
</span><span class="boring"> iterator &amp;<span class="hljs-keyword">operator</span>+=(<span class="hljs-keyword">ptrdiff_t</span>) <span class="hljs-keyword">noexcept</span>;
</span><span class="boring"> iterator &amp;<span class="hljs-keyword">operator</span>-=(<span class="hljs-keyword">ptrdiff_t</span>) <span class="hljs-keyword">noexcept</span>;
</span><span class="boring"> iterator <span class="hljs-keyword">operator</span>+(<span class="hljs-keyword">ptrdiff_t</span>) <span class="hljs-keyword">const</span> <span class="hljs-keyword">noexcept</span>;
</span><span class="boring"> iterator <span class="hljs-keyword">operator</span>-(<span class="hljs-keyword">ptrdiff_t</span>) <span class="hljs-keyword">const</span> <span class="hljs-keyword">noexcept</span>;
</span><span class="boring"> <span class="hljs-keyword">ptrdiff_t</span> <span class="hljs-keyword">operator</span>-(<span class="hljs-keyword">const</span> iterator &amp;) <span class="hljs-keyword">const</span> <span class="hljs-keyword">noexcept</span>;
</span><span class="boring">
</span><span class="boring"> <span class="hljs-keyword">bool</span> <span class="hljs-keyword">operator</span>==(<span class="hljs-keyword">const</span> iterator &amp;) <span class="hljs-keyword">const</span> <span class="hljs-keyword">noexcept</span>;
</span><span class="boring"> <span class="hljs-keyword">bool</span> <span class="hljs-keyword">operator</span>!=(<span class="hljs-keyword">const</span> iterator &amp;) <span class="hljs-keyword">const</span> <span class="hljs-keyword">noexcept</span>;
</span><span class="boring"> <span class="hljs-keyword">bool</span> <span class="hljs-keyword">operator</span>&lt;(<span class="hljs-keyword">const</span> iterator &amp;) <span class="hljs-keyword">const</span> <span class="hljs-keyword">noexcept</span>;
</span><span class="boring"> <span class="hljs-keyword">bool</span> <span class="hljs-keyword">operator</span>&gt;(<span class="hljs-keyword">const</span> iterator &amp;) <span class="hljs-keyword">const</span> <span class="hljs-keyword">noexcept</span>;
</span><span class="boring"> <span class="hljs-keyword">bool</span> <span class="hljs-keyword">operator</span>&lt;=(<span class="hljs-keyword">const</span> iterator &amp;) <span class="hljs-keyword">const</span> <span class="hljs-keyword">noexcept</span>;
</span><span class="boring"> <span class="hljs-keyword">bool</span> <span class="hljs-keyword">operator</span>&gt;=(<span class="hljs-keyword">const</span> iterator &amp;) <span class="hljs-keyword">const</span> <span class="hljs-keyword">noexcept</span>;
</span><span class="boring">};
</span><span class="boring">
</span><span class="boring">} <span class="hljs-comment">// namespace rust</span>
</span></code></pre>
<h3 id="restrictions"><a class="header" href="#restrictions">Restrictions:</a></h3>
<p>T must not be an opaque Rust type or opaque C++ type. Support for opaque Rust
types in slices is coming.</p>
<p>Allowed as function argument or return value. Not supported in shared structs.</p>
<p>Only rust::Slice&lt;const T&gt; is copy-assignable, not rust::Slice&lt;T&gt;. (Both are
move-assignable.) You'll need to write std::move occasionally as a reminder that
accidentally exposing overlapping &amp;mut [T] to Rust is UB.</p>
<h2 id="example"><a class="header" href="#example">Example</a></h2>
<p>This example is a C++ program that constructs a slice containing JSON data (by
reading from stdin, but it could be from anywhere), then calls into Rust to
pretty-print that JSON data into a std::string via the <a href="https://github.com/serde-rs/json">serde_json</a> and
<a href="https://github.com/sfackler/serde-transcode">serde_transcode</a> crates.</p>
<pre><code class="noplayground hidelines hide-boring hljs"><span class="hljs-comment">// src/main.rs</span>
<span class="hljs-meta">#![no_main]</span> <span class="hljs-comment">// main defined in C++ by main.cc</span>
<span class="hljs-keyword">use</span> cxx::CxxString;
<span class="hljs-keyword">use</span> std::io::{<span class="hljs-keyword">self</span>, Write};
<span class="hljs-keyword">use</span> std::pin::Pin;
<span class="hljs-meta">#[cxx::bridge]</span>
<span class="hljs-keyword">mod</span> ffi {
<span class="hljs-keyword">extern</span> <span class="hljs-string">&quot;Rust&quot;</span> {
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">prettify_json</span></span>(input: &amp;[<span class="hljs-built_in">u8</span>], output: Pin&lt;&amp;<span class="hljs-keyword">mut</span> CxxString&gt;) -&gt; <span class="hljs-built_in">Result</span>&lt;()&gt;;
}
}
<span class="hljs-class"><span class="hljs-keyword">struct</span> <span class="hljs-title">WriteToCxxString</span></span>&lt;<span class="hljs-symbol">&#x27;a</span>&gt;(Pin&lt;&amp;<span class="hljs-symbol">&#x27;a</span> <span class="hljs-keyword">mut</span> CxxString&gt;);
<span class="hljs-keyword">impl</span>&lt;<span class="hljs-symbol">&#x27;a</span>&gt; Write <span class="hljs-keyword">for</span> WriteToCxxString&lt;<span class="hljs-symbol">&#x27;a</span>&gt; {
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">write</span></span>(&amp;<span class="hljs-keyword">mut</span> <span class="hljs-keyword">self</span>, buf: &amp;[<span class="hljs-built_in">u8</span>]) -&gt; io::<span class="hljs-built_in">Result</span>&lt;<span class="hljs-built_in">usize</span>&gt; {
<span class="hljs-keyword">self</span>.<span class="hljs-number">0</span>.as_mut().push_bytes(buf);
<span class="hljs-literal">Ok</span>(buf.len())
}
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">flush</span></span>(&amp;<span class="hljs-keyword">mut</span> <span class="hljs-keyword">self</span>) -&gt; io::<span class="hljs-built_in">Result</span>&lt;()&gt; {
<span class="hljs-literal">Ok</span>(())
}
}
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">prettify_json</span></span>(input: &amp;[<span class="hljs-built_in">u8</span>], output: Pin&lt;&amp;<span class="hljs-keyword">mut</span> CxxString&gt;) -&gt; serde_json::<span class="hljs-built_in">Result</span>&lt;()&gt; {
<span class="hljs-keyword">let</span> writer = WriteToCxxString(output);
<span class="hljs-keyword">let</span> <span class="hljs-keyword">mut</span> deserializer = serde_json::Deserializer::from_slice(input);
<span class="hljs-keyword">let</span> <span class="hljs-keyword">mut</span> serializer = serde_json::Serializer::pretty(writer);
serde_transcode::transcode(&amp;<span class="hljs-keyword">mut</span> deserializer, &amp;<span class="hljs-keyword">mut</span> serializer)
}</code></pre>
<pre><code class="hidelines hide-boring hljs"><span class="hljs-comment">// src/main.cc</span>
<span class="hljs-meta">#<span class="hljs-meta-keyword">include</span> <span class="hljs-meta-string">&quot;example/src/main.rs.h&quot;</span></span>
<span class="hljs-meta">#<span class="hljs-meta-keyword">include</span> <span class="hljs-meta-string">&lt;iostream&gt;</span></span>
<span class="hljs-meta">#<span class="hljs-meta-keyword">include</span> <span class="hljs-meta-string">&lt;iterator&gt;</span></span>
<span class="hljs-meta">#<span class="hljs-meta-keyword">include</span> <span class="hljs-meta-string">&lt;string&gt;</span></span>
<span class="hljs-meta">#<span class="hljs-meta-keyword">include</span> <span class="hljs-meta-string">&lt;vector&gt;</span></span>
<span class="hljs-function"><span class="hljs-keyword">int</span> <span class="hljs-title">main</span><span class="hljs-params">()</span> </span>{
<span class="hljs-comment">// Read json from stdin.</span>
<span class="hljs-built_in">std</span>::istreambuf_iterator&lt;<span class="hljs-keyword">char</span>&gt; begin{<span class="hljs-built_in">std</span>::<span class="hljs-built_in">cin</span>}, end;
<span class="hljs-built_in">std</span>::<span class="hljs-built_in">vector</span>&lt;<span class="hljs-keyword">unsigned</span> <span class="hljs-keyword">char</span>&gt; input{begin, end};
rust::Slice&lt;<span class="hljs-keyword">const</span> <span class="hljs-keyword">uint8_t</span>&gt; slice{input.data(), input.size()};
<span class="hljs-comment">// Prettify using serde_json and serde_transcode.</span>
<span class="hljs-built_in">std</span>::<span class="hljs-built_in">string</span> output;
prettify_json(slice, output);
<span class="hljs-comment">// Write to stdout.</span>
<span class="hljs-built_in">std</span>::<span class="hljs-built_in">cout</span> &lt;&lt; output &lt;&lt; <span class="hljs-built_in">std</span>::<span class="hljs-built_in">endl</span>;
}
</code></pre>
<p>Testing the example:</p>
<pre><code class="hidelines hide-boring hljs"><span class="hljs-meta">$</span><span class="bash"> <span class="hljs-built_in">echo</span> <span class="hljs-string">&#x27;{&quot;fearless&quot;:&quot;concurrency&quot;}&#x27;</span> | cargo run</span>
Finished dev [unoptimized + debuginfo] target(s) in 0.02s
Running `target/debug/example`
{
&quot;fearless&quot;: &quot;concurrency&quot;
}
</code></pre>
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