169 lines
8.7 KiB
HTML
169 lines
8.7 KiB
HTML
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<!DOCTYPE html>
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<html lang="en">
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<meta name="generator" content="rustdoc">
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<meta name="description" content="API documentation for the Rust `from_reader` fn in crate `serde_json`.">
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<meta name="keywords" content="rust, rustlang, rust-lang, from_reader">
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<title>serde_json::de::from_reader - Rust</title>
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<link rel="stylesheet" type="text/css" href="../../normalize.css">
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<div class="sidebar-menu">☰</div>
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<p class='location'><a href='../index.html'>serde_json</a>::<wbr><a href='index.html'>de</a></p><script>window.sidebarCurrent = {name: 'from_reader', ty: 'fn', relpath: ''};</script><script defer src="sidebar-items.js"></script>
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type="search">
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<section id='main' class="content">
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<h1 class='fqn'><span class='in-band'>Function <a href='../index.html'>serde_json</a>::<wbr><a href='index.html'>de</a>::<wbr><a class="fn" href=''>from_reader</a></span><span class='out-of-band'><span id='render-detail'>
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[<span class='inner'>−</span>]
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</a>
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</span><a class='srclink' href='../../src/serde_json/de.rs.html#2173-2179' title='goto source code'>[src]</a></span></h1>
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<pre class='rust fn'>pub fn from_reader<R, T>(rdr: R) -> <a class="type" href="../../serde_json/type.Result.html" title="type serde_json::Result">Result</a><T> <span class="where fmt-newline">where<br> R: <a class="trait" href="https://doc.rust-lang.org/nightly/std/io/trait.Read.html" title="trait std::io::Read">Read</a>,<br> T: <a class="trait" href="../../serde/de/trait.DeserializeOwned.html" title="trait serde::de::DeserializeOwned">DeserializeOwned</a>, </span></pre><div class='docblock'><p>Deserialize an instance of type <code>T</code> from an IO stream of JSON.</p>
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<h1 id="errors" class="section-header"><a href="#errors">Errors</a></h1>
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<p>This conversion can fail if the structure of the input does not match the
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structure expected by <code>T</code>, for example if <code>T</code> is a struct type but the input
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contains something other than a JSON map. It can also fail if the structure
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is correct but <code>T</code>'s implementation of <code>Deserialize</code> decides that something
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is wrong with the data, for example required struct fields are missing from
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the JSON map or some number is too big to fit in the expected primitive
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type.</p>
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<pre class="rust rust-example-rendered">
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<span class="attribute">#[<span class="ident">macro_use</span>]</span>
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<span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">serde_derive</span>;
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<span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">serde</span>;
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<span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">serde_json</span>;
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<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">error</span>::<span class="ident">Error</span>;
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<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">fs</span>::<span class="ident">File</span>;
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<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">path</span>::<span class="ident">Path</span>;
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<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Deserialize</span>, <span class="ident">Debug</span>)]</span>
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<span class="kw">struct</span> <span class="ident">User</span> {
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<span class="ident">fingerprint</span>: <span class="ident">String</span>,
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<span class="ident">location</span>: <span class="ident">String</span>,
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}
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<span class="kw">fn</span> <span class="ident">read_user_from_file</span><span class="op"><</span><span class="ident">P</span>: <span class="ident">AsRef</span><span class="op"><</span><span class="ident">Path</span><span class="op">>></span>(<span class="ident">path</span>: <span class="ident">P</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span><span class="ident">User</span>, <span class="ident">Box</span><span class="op"><</span><span class="ident">Error</span><span class="op">>></span> {
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<span class="comment">// Open the file in read-only mode.</span>
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<span class="kw">let</span> <span class="ident">file</span> <span class="op">=</span> <span class="ident">File</span>::<span class="ident">open</span>(<span class="ident">path</span>)<span class="question-mark">?</span>;
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<span class="comment">// Read the JSON contents of the file as an instance of `User`.</span>
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<span class="kw">let</span> <span class="ident">u</span> <span class="op">=</span> <span class="ident">serde_json</span>::<span class="ident">from_reader</span>(<span class="ident">file</span>)<span class="question-mark">?</span>;
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<span class="comment">// Return the `User`.</span>
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<span class="prelude-val">Ok</span>(<span class="ident">u</span>)
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}
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<span class="kw">fn</span> <span class="ident">main</span>() {
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<span class="kw">let</span> <span class="ident">u</span> <span class="op">=</span> <span class="ident">read_user_from_file</span>(<span class="string">"test.json"</span>).<span class="ident">unwrap</span>();
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<span class="macro">println</span><span class="macro">!</span>(<span class="string">"{:#?}"</span>, <span class="ident">u</span>);
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}</pre>
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</div></section>
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<h1 class="hidden">Help</h1>
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Accepted types are: <code>fn</code>, <code>mod</code>,
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<code>struct</code>, <code>enum</code>,
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<code>trait</code>, <code>type</code>, <code>macro</code>,
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and <code>const</code>.
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Search functions by type signature (e.g.
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window.rootPath = "../../";
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