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<p class='location'>Crate futures</p><div class="sidebar-elems"><div class="block items"><ul><li><a href="#reexports">Re-exports</a></li><li><a href="#modules">Modules</a></li><li><a href="#macros">Macros</a></li><li><a href="#enums">Enums</a></li><li><a href="#types">Type Definitions</a></li></ul></div><p class='location'></p><script>window.sidebarCurrent = {name: 'futures', ty: 'mod', relpath: '../'};</script></div>
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<section id='main' class="content">
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<h1 class='fqn'><span class='in-band'>Crate <a class="mod" href=''>futures</a></span><span class='out-of-band'><span id='render-detail'>
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[<span class='inner'>−</span>]
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</span><a class='srclink' href='../src/futures/lib.rs.html#1-265' title='goto source code'>[src]</a></span></h1>
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<div class='docblock'><p>Zero-cost Futures in Rust</p>
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<p>This library is an implementation of futures in Rust which aims to provide
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a robust implementation of handling asynchronous computations, ergonomic
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composition and usage, and zero-cost abstractions over what would otherwise
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be written by hand.</p>
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<p>Futures are a concept for an object which is a proxy for another value that
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may not be ready yet. For example issuing an HTTP request may return a
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future for the HTTP response, as it probably hasn't arrived yet. With an
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object representing a value that will eventually be available, futures allow
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for powerful composition of tasks through basic combinators that can perform
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operations like chaining computations, changing the types of futures, or
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waiting for two futures to complete at the same time.</p>
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<p>You can find extensive tutorials and documentations at <a href="https://tokio.rs">https://tokio.rs</a>
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for both this crate (asynchronous programming in general) as well as the
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Tokio stack to perform async I/O with.</p>
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<h2 id="installation" class="section-header"><a href="#installation">Installation</a></h2>
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<p>Add this to your <code>Cargo.toml</code>:</p>
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<pre><code class="language-toml">[dependencies]
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futures = "0.1"
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</code></pre>
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<h2 id="examples" class="section-header"><a href="#examples">Examples</a></h2>
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<p>Let's take a look at a few examples of how futures might be used:</p>
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<pre class="rust rust-example-rendered">
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<span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">futures</span>;
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<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">io</span>;
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<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">time</span>::<span class="ident">Duration</span>;
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<span class="kw">use</span> <span class="ident">futures</span>::<span class="ident">prelude</span>::<span class="kw-2">*</span>;
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<span class="kw">use</span> <span class="ident">futures</span>::<span class="ident">future</span>::<span class="ident">Map</span>;
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<span class="comment">// A future is actually a trait implementation, so we can generically take a</span>
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<span class="comment">// future of any integer and return back a future that will resolve to that</span>
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<span class="comment">// value plus 10 more.</span>
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<span class="comment">//</span>
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<span class="comment">// Note here that like iterators, we're returning the `Map` combinator in</span>
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<span class="comment">// the futures crate, not a boxed abstraction. This is a zero-cost</span>
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<span class="comment">// construction of a future.</span>
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<span class="kw">fn</span> <span class="ident">add_ten</span><span class="op"><</span><span class="ident">F</span><span class="op">></span>(<span class="ident">future</span>: <span class="ident">F</span>) <span class="op">-></span> <span class="ident">Map</span><span class="op"><</span><span class="ident">F</span>, <span class="kw">fn</span>(<span class="ident">i32</span>) <span class="op">-></span> <span class="ident">i32</span><span class="op">></span>
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<span class="kw">where</span> <span class="ident">F</span>: <span class="ident">Future</span><span class="op"><</span><span class="ident">Item</span><span class="op">=</span><span class="ident">i32</span><span class="op">></span>,
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{
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<span class="kw">fn</span> <span class="ident">add</span>(<span class="ident">a</span>: <span class="ident">i32</span>) <span class="op">-></span> <span class="ident">i32</span> { <span class="ident">a</span> <span class="op">+</span> <span class="number">10</span> }
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<span class="ident">future</span>.<span class="ident">map</span>(<span class="ident">add</span>)
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}
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<span class="comment">// Not only can we modify one future, but we can even compose them together!</span>
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<span class="comment">// Here we have a function which takes two futures as input, and returns a</span>
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<span class="comment">// future that will calculate the sum of their two values.</span>
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<span class="comment">//</span>
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<span class="comment">// Above we saw a direct return value of the `Map` combinator, but</span>
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<span class="comment">// performance isn't always critical and sometimes it's more ergonomic to</span>
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<span class="comment">// return a trait object like we do here. Note though that there's only one</span>
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<span class="comment">// allocation here, not any for the intermediate futures.</span>
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<span class="kw">fn</span> <span class="ident">add</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">A</span>, <span class="ident">B</span><span class="op">></span>(<span class="ident">a</span>: <span class="ident">A</span>, <span class="ident">b</span>: <span class="ident">B</span>) <span class="op">-></span> <span class="ident">Box</span><span class="op"><</span><span class="ident">Future</span><span class="op"><</span><span class="ident">Item</span><span class="op">=</span><span class="ident">i32</span>, <span class="ident">Error</span><span class="op">=</span><span class="ident">A</span>::<span class="ident">Error</span><span class="op">></span> <span class="op">+</span> <span class="lifetime">'a</span><span class="op">></span>
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<span class="kw">where</span> <span class="ident">A</span>: <span class="ident">Future</span><span class="op"><</span><span class="ident">Item</span><span class="op">=</span><span class="ident">i32</span><span class="op">></span> <span class="op">+</span> <span class="lifetime">'a</span>,
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<span class="ident">B</span>: <span class="ident">Future</span><span class="op"><</span><span class="ident">Item</span><span class="op">=</span><span class="ident">i32</span>, <span class="ident">Error</span><span class="op">=</span><span class="ident">A</span>::<span class="ident">Error</span><span class="op">></span> <span class="op">+</span> <span class="lifetime">'a</span>,
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{
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<span class="ident">Box</span>::<span class="ident">new</span>(<span class="ident">a</span>.<span class="ident">join</span>(<span class="ident">b</span>).<span class="ident">map</span>(<span class="op">|</span>(<span class="ident">a</span>, <span class="ident">b</span>)<span class="op">|</span> <span class="ident">a</span> <span class="op">+</span> <span class="ident">b</span>))
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}
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<span class="comment">// Futures also allow chaining computations together, starting another after</span>
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<span class="comment">// the previous finishes. Here we wait for the first computation to finish,</span>
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<span class="comment">// and then decide what to do depending on the result.</span>
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<span class="kw">fn</span> <span class="ident">download_timeout</span>(<span class="ident">url</span>: <span class="kw-2">&</span><span class="ident">str</span>,
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<span class="ident">timeout_dur</span>: <span class="ident">Duration</span>)
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<span class="op">-></span> <span class="ident">Box</span><span class="op"><</span><span class="ident">Future</span><span class="op"><</span><span class="ident">Item</span><span class="op">=</span><span class="ident">Vec</span><span class="op"><</span><span class="ident">u8</span><span class="op">></span>, <span class="ident">Error</span><span class="op">=</span><span class="ident">io</span>::<span class="ident">Error</span><span class="op">>></span> {
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<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">io</span>;
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<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">net</span>::{<span class="ident">SocketAddr</span>, <span class="ident">TcpStream</span>};
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<span class="kw">type</span> <span class="ident">IoFuture</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="op">=</span> <span class="ident">Box</span><span class="op"><</span><span class="ident">Future</span><span class="op"><</span><span class="ident">Item</span><span class="op">=</span><span class="ident">T</span>, <span class="ident">Error</span><span class="op">=</span><span class="ident">io</span>::<span class="ident">Error</span><span class="op">>></span>;
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<span class="comment">// First thing to do is we need to resolve our URL to an address. This</span>
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<span class="comment">// will likely perform a DNS lookup which may take some time.</span>
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<span class="kw">let</span> <span class="ident">addr</span> <span class="op">=</span> <span class="ident">resolve</span>(<span class="ident">url</span>);
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<span class="comment">// After we acquire the address, we next want to open up a TCP</span>
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<span class="comment">// connection.</span>
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<span class="kw">let</span> <span class="ident">tcp</span> <span class="op">=</span> <span class="ident">addr</span>.<span class="ident">and_then</span>(<span class="op">|</span><span class="ident">addr</span><span class="op">|</span> <span class="ident">connect</span>(<span class="kw-2">&</span><span class="ident">addr</span>));
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<span class="comment">// After the TCP connection is established and ready to go, we're off to</span>
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<span class="comment">// the races!</span>
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<span class="kw">let</span> <span class="ident">data</span> <span class="op">=</span> <span class="ident">tcp</span>.<span class="ident">and_then</span>(<span class="op">|</span><span class="ident">conn</span><span class="op">|</span> <span class="ident">download</span>(<span class="ident">conn</span>));
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<span class="comment">// That all might take awhile, though, so let's not wait too long for it</span>
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<span class="comment">// to all come back. The `select` combinator here returns a future which</span>
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<span class="comment">// resolves to the first value that's ready plus the next future.</span>
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<span class="comment">//</span>
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<span class="comment">// Note we can also use the `then` combinator which is similar to</span>
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<span class="comment">// `and_then` above except that it receives the result of the</span>
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<span class="comment">// computation, not just the successful value.</span>
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<span class="comment">//</span>
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<span class="comment">// Again note that all the above calls to `and_then` and the below calls</span>
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<span class="comment">// to `map` and such require no allocations. We only ever allocate once</span>
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<span class="comment">// we hit the `Box::new()` call at the end here, which means we've built</span>
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<span class="comment">// up a relatively involved computation with only one box, and even that</span>
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<span class="comment">// was optional!</span>
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<span class="kw">let</span> <span class="ident">data</span> <span class="op">=</span> <span class="ident">data</span>.<span class="ident">map</span>(<span class="prelude-val">Ok</span>);
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<span class="kw">let</span> <span class="ident">timeout</span> <span class="op">=</span> <span class="ident">timeout</span>(<span class="ident">timeout_dur</span>).<span class="ident">map</span>(<span class="prelude-val">Err</span>);
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<span class="kw">let</span> <span class="ident">ret</span> <span class="op">=</span> <span class="ident">data</span>.<span class="ident">select</span>(<span class="ident">timeout</span>).<span class="ident">then</span>(<span class="op">|</span><span class="ident">result</span><span class="op">|</span> {
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<span class="kw">match</span> <span class="ident">result</span> {
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<span class="comment">// One future succeeded, and it was the one which was</span>
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<span class="comment">// downloading data from the connection.</span>
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<span class="prelude-val">Ok</span>((<span class="prelude-val">Ok</span>(<span class="ident">data</span>), <span class="ident">_other_future</span>)) <span class="op">=></span> <span class="prelude-val">Ok</span>(<span class="ident">data</span>),
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<span class="comment">// The timeout fired, and otherwise no error was found, so</span>
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<span class="comment">// we translate this to an error.</span>
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<span class="prelude-val">Ok</span>((<span class="prelude-val">Err</span>(<span class="ident">_timeout</span>), <span class="ident">_other_future</span>)) <span class="op">=></span> {
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<span class="prelude-val">Err</span>(<span class="ident">io</span>::<span class="ident">Error</span>::<span class="ident">new</span>(<span class="ident">io</span>::<span class="ident">ErrorKind</span>::<span class="ident">Other</span>, <span class="string">"timeout"</span>))
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}
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<span class="comment">// A normal I/O error happened, so we pass that on through.</span>
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<span class="prelude-val">Err</span>((<span class="ident">e</span>, <span class="ident">_other_future</span>)) <span class="op">=></span> <span class="prelude-val">Err</span>(<span class="ident">e</span>),
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}
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});
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<span class="kw">return</span> <span class="ident">Box</span>::<span class="ident">new</span>(<span class="ident">ret</span>);
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<span class="kw">fn</span> <span class="ident">resolve</span>(<span class="ident">url</span>: <span class="kw-2">&</span><span class="ident">str</span>) <span class="op">-></span> <span class="ident">IoFuture</span><span class="op"><</span><span class="ident">SocketAddr</span><span class="op">></span> {
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<span class="comment">// ...</span>
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}
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<span class="kw">fn</span> <span class="ident">connect</span>(<span class="ident">hostname</span>: <span class="kw-2">&</span><span class="ident">SocketAddr</span>) <span class="op">-></span> <span class="ident">IoFuture</span><span class="op"><</span><span class="ident">TcpStream</span><span class="op">></span> {
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<span class="comment">// ...</span>
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}
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<span class="kw">fn</span> <span class="ident">download</span>(<span class="ident">stream</span>: <span class="ident">TcpStream</span>) <span class="op">-></span> <span class="ident">IoFuture</span><span class="op"><</span><span class="ident">Vec</span><span class="op"><</span><span class="ident">u8</span><span class="op">>></span> {
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<span class="comment">// ...</span>
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}
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<span class="kw">fn</span> <span class="ident">timeout</span>(<span class="ident">stream</span>: <span class="ident">Duration</span>) <span class="op">-></span> <span class="ident">IoFuture</span><span class="op"><</span>()<span class="op">></span> {
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<span class="comment">// ...</span>
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}
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}</pre>
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<p>Some more information can also be found in the <a href="https://github.com/rust-lang-nursery/futures-rs#futures-rs">README</a> for now, but
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otherwise feel free to jump in to the docs below!</p>
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</div><h2 id='reexports' class='section-header'><a href="#reexports">Re-exports</a></h2>
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||
<table><tr><td><code>pub use future::<a class="trait" href="../futures/future/trait.Future.html" title="trait futures::future::Future">Future</a>;</code></td></tr><tr><td><code>pub use future::<a class="trait" href="../futures/future/trait.IntoFuture.html" title="trait futures::future::IntoFuture">IntoFuture</a>;</code></td></tr><tr><td><code>pub use stream::<a class="trait" href="../futures/stream/trait.Stream.html" title="trait futures::stream::Stream">Stream</a>;</code></td></tr><tr><td><code>pub use sink::<a class="trait" href="../futures/sink/trait.Sink.html" title="trait futures::sink::Sink">Sink</a>;</code></td></tr></table><h2 id='modules' class='section-header'><a href="#modules">Modules</a></h2>
|
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<table>
|
||
<tr class=' module-item'>
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<td><a class="mod" href="executor/index.html"
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title='mod futures::executor'>executor</a></td>
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||
<td class='docblock-short'>
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||
<p>Executors</p>
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||
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||
</td>
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</tr>
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<tr class=' module-item'>
|
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<td><a class="mod" href="future/index.html"
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title='mod futures::future'>future</a></td>
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<td class='docblock-short'>
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<p>Futures</p>
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</td>
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</tr>
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<tr class=' module-item'>
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<td><a class="mod" href="prelude/index.html"
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title='mod futures::prelude'>prelude</a></td>
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||
<td class='docblock-short'>
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||
<p>A "prelude" for crates using the <code>futures</code> crate.</p>
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||
|
||
</td>
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||
</tr>
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<tr class=' module-item'>
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<td><a class="mod" href="sink/index.html"
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title='mod futures::sink'>sink</a></td>
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||
<td class='docblock-short'>
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<p>Asynchronous sinks</p>
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||
|
||
</td>
|
||
</tr>
|
||
<tr class=' module-item'>
|
||
<td><a class="mod" href="stream/index.html"
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||
title='mod futures::stream'>stream</a></td>
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||
<td class='docblock-short'>
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||
<p>Asynchronous streams</p>
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||
|
||
</td>
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||
</tr>
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||
<tr class=' module-item'>
|
||
<td><a class="mod" href="sync/index.html"
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||
title='mod futures::sync'>sync</a></td>
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||
<td class='docblock-short'>
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||
<p>Future-aware synchronization</p>
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||
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</td>
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||
</tr>
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<tr class=' module-item'>
|
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<td><a class="mod" href="task/index.html"
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||
title='mod futures::task'>task</a></td>
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<td class='docblock-short'>
|
||
<p>Tasks used to drive a future computation</p>
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||
|
||
</td>
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</tr>
|
||
<tr class=' module-item'>
|
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<td><a class="mod" href="unsync/index.html"
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title='mod futures::unsync'>unsync</a></td>
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<td class='docblock-short'>
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<p>Future-aware single-threaded synchronization</p>
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</td>
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||
</tr></table><h2 id='macros' class='section-header'><a href="#macros">Macros</a></h2>
|
||
<table>
|
||
<tr class=' module-item'>
|
||
<td><a class="macro" href="macro.task_local.html"
|
||
title='macro futures::task_local'>task_local</a></td>
|
||
<td class='docblock-short'>
|
||
<p>A macro to create a <code>static</code> of type <code>LocalKey</code></p>
|
||
|
||
</td>
|
||
</tr>
|
||
<tr class=' module-item'>
|
||
<td><a class="macro" href="macro.try_ready.html"
|
||
title='macro futures::try_ready'>try_ready</a></td>
|
||
<td class='docblock-short'>
|
||
<p>A macro for extracting the successful type of a <code>Poll<T, E></code>.</p>
|
||
|
||
</td>
|
||
</tr></table><h2 id='enums' class='section-header'><a href="#enums">Enums</a></h2>
|
||
<table>
|
||
<tr class=' module-item'>
|
||
<td><a class="enum" href="enum.Async.html"
|
||
title='enum futures::Async'>Async</a></td>
|
||
<td class='docblock-short'>
|
||
<p>Return type of future, indicating whether a value is ready or not.</p>
|
||
|
||
</td>
|
||
</tr>
|
||
<tr class=' module-item'>
|
||
<td><a class="enum" href="enum.AsyncSink.html"
|
||
title='enum futures::AsyncSink'>AsyncSink</a></td>
|
||
<td class='docblock-short'>
|
||
<p>The result of an asynchronous attempt to send a value to a sink.</p>
|
||
|
||
</td>
|
||
</tr></table><h2 id='types' class='section-header'><a href="#types">Type Definitions</a></h2>
|
||
<table>
|
||
<tr class=' module-item'>
|
||
<td><a class="type" href="type.Poll.html"
|
||
title='type futures::Poll'>Poll</a></td>
|
||
<td class='docblock-short'>
|
||
<p>Return type of the <code>Future::poll</code> method, indicates whether a future's value
|
||
is ready or not.</p>
|
||
|
||
</td>
|
||
</tr>
|
||
<tr class=' module-item'>
|
||
<td><a class="type" href="type.StartSend.html"
|
||
title='type futures::StartSend'>StartSend</a></td>
|
||
<td class='docblock-short'>
|
||
<p>Return type of the <code>Sink::start_send</code> method, indicating the outcome of a
|
||
send attempt. See <code>AsyncSink</code> for more details.</p>
|
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