248 lines
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248 lines
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HTML
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<meta name="description" content="API documentation for the Rust `value` mod in crate `serde_json`.">
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<title>serde_json::value - Rust</title>
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<div class="sidebar-menu">☰</div>
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<p class='location'>Module value</p><div class="sidebar-elems"><div class="block items"><ul><li><a href="#reexports">Re-exports</a></li><li><a href="#structs">Structs</a></li><li><a href="#enums">Enums</a></li><li><a href="#traits">Traits</a></li><li><a href="#functions">Functions</a></li></ul></div><p class='location'><a href='../index.html'>serde_json</a></p><script>window.sidebarCurrent = {name: 'value', ty: 'mod', relpath: '../'};</script><script defer src="../sidebar-items.js"></script></div>
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autocomplete="off"
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placeholder="Click or press ‘S’ to search, ‘?’ for more options…"
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type="search">
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</nav>
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<section id='main' class="content">
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<h1 class='fqn'><span class='in-band'>Module <a href='../index.html'>serde_json</a>::<wbr><a class="mod" href=''>value</a></span><span class='out-of-band'><span id='render-detail'>
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<a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">
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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/value/mod.rs.html#9-1126' title='goto source code'>[src]</a></span></h1>
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<div class='docblock'><p>The Value enum, a loosely typed way of representing any valid JSON value.</p>
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<h1 id="constructing-json" class="section-header"><a href="#constructing-json">Constructing JSON</a></h1>
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<p>Serde JSON provides a <a href="https://docs.serde.rs/serde_json/macro.json.html"><code>json!</code> macro</a> to build <code>serde_json::Value</code>
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objects with very natural JSON syntax. In order to use this macro,
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<code>serde_json</code> needs to be imported with the <code>#[macro_use]</code> attribute.</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_json</span>;
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<span class="kw">fn</span> <span class="ident">main</span>() {
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<span class="comment">// The type of `john` is `serde_json::Value`</span>
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<span class="kw">let</span> <span class="ident">john</span> <span class="op">=</span> <span class="macro">json</span><span class="macro">!</span>({
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<span class="string">"name"</span>: <span class="string">"John Doe"</span>,
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<span class="string">"age"</span>: <span class="number">43</span>,
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<span class="string">"phones"</span>: [
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<span class="string">"+44 1234567"</span>,
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<span class="string">"+44 2345678"</span>
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]
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});
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<span class="macro">println</span><span class="macro">!</span>(<span class="string">"first phone number: {}"</span>, <span class="ident">john</span>[<span class="string">"phones"</span>][<span class="number">0</span>]);
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<span class="comment">// Convert to a string of JSON and print it out</span>
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<span class="macro">println</span><span class="macro">!</span>(<span class="string">"{}"</span>, <span class="ident">john</span>.<span class="ident">to_string</span>());
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}</pre>
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<p>The <code>Value::to_string()</code> function converts a <code>serde_json::Value</code> into a
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<code>String</code> of JSON text.</p>
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<p>One neat thing about the <code>json!</code> macro is that variables and expressions can
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be interpolated directly into the JSON value as you are building it. Serde
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will check at compile time that the value you are interpolating is able to
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be represented as JSON.</p>
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<pre class="rust rust-example-rendered">
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<span class="kw">let</span> <span class="ident">full_name</span> <span class="op">=</span> <span class="string">"John Doe"</span>;
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<span class="kw">let</span> <span class="ident">age_last_year</span> <span class="op">=</span> <span class="number">42</span>;
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<span class="comment">// The type of `john` is `serde_json::Value`</span>
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<span class="kw">let</span> <span class="ident">john</span> <span class="op">=</span> <span class="macro">json</span><span class="macro">!</span>({
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<span class="string">"name"</span>: <span class="ident">full_name</span>,
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<span class="string">"age"</span>: <span class="ident">age_last_year</span> <span class="op">+</span> <span class="number">1</span>,
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<span class="string">"phones"</span>: [
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<span class="macro">format</span><span class="macro">!</span>(<span class="string">"+44 {}"</span>, <span class="ident">random_phone</span>())
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]
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});</pre>
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<p>A string of JSON data can be parsed into a <code>serde_json::Value</code> by the
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<a href="https://docs.serde.rs/serde_json/de/fn.from_str.html"><code>serde_json::from_str</code></a> function. There is also
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<a href="https://docs.serde.rs/serde_json/de/fn.from_slice.html"><code>from_slice</code></a> for parsing from a byte slice &[u8] and
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<a href="https://docs.serde.rs/serde_json/de/fn.from_reader.html"><code>from_reader</code></a> for parsing from any <code>io::Read</code> like a File or
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a TCP stream.</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">serde_json</span>;
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<span class="kw">use</span> <span class="ident">serde_json</span>::{<span class="ident">Value</span>, <span class="ident">Error</span>};
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<span class="kw">fn</span> <span class="ident">untyped_example</span>() <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span>(), <span class="ident">Error</span><span class="op">></span> {
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<span class="comment">// Some JSON input data as a &str. Maybe this comes from the user.</span>
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<span class="kw">let</span> <span class="ident">data</span> <span class="op">=</span> <span class="string">r#"{
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"name": "John Doe",
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"age": 43,
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"phones": [
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"+44 1234567",
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"+44 2345678"
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]
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}"#</span>;
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<span class="comment">// Parse the string of data into serde_json::Value.</span>
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<span class="kw">let</span> <span class="ident">v</span>: <span class="ident">Value</span> <span class="op">=</span> <span class="ident">serde_json</span>::<span class="ident">from_str</span>(<span class="ident">data</span>)<span class="question-mark">?</span>;
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<span class="comment">// Access parts of the data by indexing with square brackets.</span>
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<span class="macro">println</span><span class="macro">!</span>(<span class="string">"Please call {} at the number {}"</span>, <span class="ident">v</span>[<span class="string">"name"</span>], <span class="ident">v</span>[<span class="string">"phones"</span>][<span class="number">0</span>]);
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<span class="prelude-val">Ok</span>(())
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}</pre>
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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 map::<a class="struct" href="../../serde_json/map/struct.Map.html" title="struct serde_json::map::Map">Map</a>;</code></td></tr></table><h2 id='structs' class='section-header'><a href="#structs">Structs</a></h2>
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<table>
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<tr class=' module-item'>
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<td><a class="struct" href="struct.Number.html"
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title='struct serde_json::value::Number'>Number</a></td>
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<td class='docblock-short'>
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<p>Represents a JSON number, whether integer or floating point.</p>
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</td>
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</tr></table><h2 id='enums' class='section-header'><a href="#enums">Enums</a></h2>
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<table>
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<tr class=' module-item'>
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<td><a class="enum" href="enum.Value.html"
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title='enum serde_json::value::Value'>Value</a></td>
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<td class='docblock-short'>
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<p>Represents any valid JSON value.</p>
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</td>
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</tr></table><h2 id='traits' class='section-header'><a href="#traits">Traits</a></h2>
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<table>
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<tr class=' module-item'>
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<td><a class="trait" href="trait.Index.html"
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title='trait serde_json::value::Index'>Index</a></td>
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<td class='docblock-short'>
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<p>A type that can be used to index into a <code>serde_json::Value</code>.</p>
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</td>
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</tr></table><h2 id='functions' class='section-header'><a href="#functions">Functions</a></h2>
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<table>
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<tr class=' module-item'>
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<td><a class="fn" href="fn.from_value.html"
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title='fn serde_json::value::from_value'>from_value</a></td>
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<td class='docblock-short'>
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<p>Interpret a <code>serde_json::Value</code> as an instance of type <code>T</code>.</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="fn" href="fn.to_value.html"
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title='fn serde_json::value::to_value'>to_value</a></td>
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<td class='docblock-short'>
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<p>Convert a <code>T</code> into <code>serde_json::Value</code> which is an enum that can represent
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any valid JSON data.</p>
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</td>
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</tr></table></section>
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<section id='search' class="content hidden"></section>
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<aside id="help" class="hidden">
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<h1 class="hidden">Help</h1>
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<div class="shortcuts">
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<h2>Keyboard Shortcuts</h2>
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<dl>
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<dt><kbd>?</kbd></dt>
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<dd>Show this help dialog</dd>
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<dd>Focus the search field</dd>
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<dd>Move up in search results</dd>
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<div class="infos">
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<h2>Search Tricks</h2>
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<p>
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Prefix searches with a type followed by a colon (e.g.
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<code>fn:</code>) to restrict the search to a given type.
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</p>
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<p>
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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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</p>
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<p>
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Search functions by type signature (e.g.
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<code>vec -> usize</code> or <code>* -> vec</code>)
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</div>
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</aside>
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<script>
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window.rootPath = "../../";
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window.currentCrate = "serde_json";
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<script src="../../main.js"></script>
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