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<a href="." >Default value for a field</a>
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<h1 id="default-value-for-a-field"><a name="default-value-for-a-field" class="plugin-anchor" href="#default-value-for-a-field"><i class="fa fa-link" aria-hidden="true"></i></a>Default value for a field</h1>
<pre><a class="playground-link" target="_blank" href="https://play.rust-lang.org/?edition=2018&gist=b238170d32f604295a1110ad912ef3ee"></a><code class="lang-rust"><span class="hljs-keyword">use</span> serde::Deserialize;
<span class="hljs-meta">#[derive(Deserialize, Debug)]</span>
<span class="hljs-class"><span class="hljs-keyword">struct</span> <span class="hljs-title">Request</span></span> {
<span class="hljs-comment">// Use the result of a function as the default if "resource" is</span>
<span class="hljs-comment">// not included in the input.</span>
<span class="hljs-meta">#[serde(default = <span class="hljs-meta-string">"default_resource"</span>)]</span>
resource: <span class="hljs-built_in">String</span>,
<span class="hljs-comment">// Use the type's implementation of std::default::Default if</span>
<span class="hljs-comment">// "timeout" is not included in the input.</span>
<span class="hljs-meta">#[serde(default)]</span>
timeout: Timeout,
<span class="hljs-comment">// Use a method from the type as the default if "priority" is not</span>
<span class="hljs-comment">// included in the input. This may also be a trait method.</span>
<span class="hljs-meta">#[serde(default = <span class="hljs-meta-string">"Priority::lowest"</span>)]</span>
priority: Priority,
}
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">default_resource</span></span>() -> <span class="hljs-built_in">String</span> {
<span class="hljs-string">"/"</span>.to_string()
}
<span class="hljs-comment">/// Timeout in seconds.</span>
<span class="hljs-meta">#[derive(Deserialize, Debug)]</span>
<span class="hljs-class"><span class="hljs-keyword">struct</span> <span class="hljs-title">Timeout</span></span>(<span class="hljs-keyword">u32</span>);
<span class="hljs-keyword">impl</span> <span class="hljs-built_in">Default</span> <span class="hljs-keyword">for</span> Timeout {
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">default</span></span>() -> <span class="hljs-keyword">Self</span> {
Timeout(<span class="hljs-number">30</span>)
}
}
<span class="hljs-meta">#[derive(Deserialize, Debug)]</span>
<span class="hljs-class"><span class="hljs-keyword">enum</span> <span class="hljs-title">Priority</span></span> { ExtraHigh, High, Normal, Low, ExtraLow }
<span class="hljs-keyword">impl</span> Priority {
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">lowest</span></span>() -> <span class="hljs-keyword">Self</span> { Priority::ExtraLow }
}
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">main</span></span>() {
<span class="hljs-keyword">let</span> json = r#<span class="hljs-string">"
[
{
"</span>resource<span class="hljs-string">": "</span>/users<span class="hljs-string">"
},
{
"</span>timeout<span class="hljs-string">": 5,
"</span>priority<span class="hljs-string">": "</span>High<span class="hljs-string">"
}
]
"</span>#;
<span class="hljs-keyword">let</span> requests: <span class="hljs-built_in">Vec</span><Request> = serde_json::from_str(json).unwrap();
<span class="hljs-comment">// The first request has resource="/users", timeout=30, priority=ExtraLow</span>
<span class="hljs-built_in">println!</span>(<span class="hljs-string">"{:?}"</span>, requests[<span class="hljs-number">0</span>]);
<span class="hljs-comment">// The second request has resource="/", timeout=5, priority=High</span>
<span class="hljs-built_in">println!</span>(<span class="hljs-string">"{:?}"</span>, requests[<span class="hljs-number">1</span>]);
}
</code></pre>
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