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<h1 id="serialize-enum-as-number"><a name="serialize-enum-as-number" class="plugin-anchor" href="#serialize-enum-as-number"><i class="fa fa-link" aria-hidden="true"></i></a>Serialize enum as number</h1>
<pre><a class="playground-link" target="_blank" href="https://play.rust-lang.org/?gist=9a8007f8860265c322b9062fe3132e59"></a><code class="lang-rust"><span class="hljs-keyword">extern</span> <span class="hljs-keyword">crate</span> serde;
<span class="hljs-keyword">extern</span> <span class="hljs-keyword">crate</span> serde_json;
<span class="hljs-keyword">use</span> std::fmt;
<span class="hljs-built_in">macro_rules!</span> enum_number {
($name:ident { $($variant:ident = $value:expr, )* }) => {
<span class="hljs-meta">#[derive(Clone, Copy, Debug, Eq, PartialEq)]</span>
<span class="hljs-keyword">pub</span> <span class="hljs-class"><span class="hljs-keyword">enum</span> $<span class="hljs-title">name</span></span> {
$($variant = $value,)*
}
<span class="hljs-keyword">impl</span> ::serde::Serialize <span class="hljs-keyword">for</span> $name {
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">serialize</span></span><S>(&<span class="hljs-keyword">self</span>, serializer: S) -> <span class="hljs-built_in">Result</span><S::<span class="hljs-literal">Ok</span>, S::Error>
<span class="hljs-keyword">where</span> S: ::serde::Serializer
{
<span class="hljs-comment">// Serialize the enum as a u64.</span>
serializer.serialize_u64(*<span class="hljs-keyword">self</span> <span class="hljs-keyword">as</span> <span class="hljs-keyword">u64</span>)
}
}
<span class="hljs-keyword">impl</span><<span class="hljs-symbol">'de</span>> ::serde::Deserialize<<span class="hljs-symbol">'de</span>> <span class="hljs-keyword">for</span> $name {
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">deserialize</span></span><D>(deserializer: D) -> <span class="hljs-built_in">Result</span><<span class="hljs-keyword">Self</span>, D::Error>
<span class="hljs-keyword">where</span> D: ::serde::Deserializer<<span class="hljs-symbol">'de</span>>
{
<span class="hljs-class"><span class="hljs-keyword">struct</span> <span class="hljs-title">Visitor</span></span>;
<span class="hljs-keyword">impl</span><<span class="hljs-symbol">'de</span>> ::serde::de::Visitor<<span class="hljs-symbol">'de</span>> <span class="hljs-keyword">for</span> Visitor {
<span class="hljs-class"><span class="hljs-keyword">type</span> <span class="hljs-title">Value</span></span> = $name;
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">expecting</span></span>(&<span class="hljs-keyword">self</span>, formatter: &<span class="hljs-keyword">mut</span> fmt::Formatter) -> fmt::<span class="hljs-built_in">Result</span> {
formatter.write_str(<span class="hljs-string">"positive integer"</span>)
}
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">visit_u64</span></span><E>(<span class="hljs-keyword">self</span>, value: <span class="hljs-keyword">u64</span>) -> <span class="hljs-built_in">Result</span><$name, E>
<span class="hljs-keyword">where</span> E: ::serde::de::Error
{
<span class="hljs-comment">// Rust does not come with a simple way of converting a</span>
<span class="hljs-comment">// number to an enum, so use a big `match`.</span>
<span class="hljs-keyword">match</span> value {
$( $value => <span class="hljs-literal">Ok</span>($name::$variant), )*
_ => <span class="hljs-literal">Err</span>(E::custom(
<span class="hljs-built_in">format!</span>(<span class="hljs-string">"unknown {} value: {}"</span>,
<span class="hljs-built_in">stringify!</span>($name), value))),
}
}
}
<span class="hljs-comment">// Deserialize the enum from a u64.</span>
deserializer.deserialize_u64(Visitor)
}
}
}
}
enum_number!(SmallNumber {
Zero = <span class="hljs-number">0</span>,
One = <span class="hljs-number">1</span>,
Two = <span class="hljs-number">2</span>,
Three = <span class="hljs-number">3</span>,
});
<span class="hljs-function"><span class="hljs-keyword">fn</span> <span class="hljs-title">main</span></span>() {
<span class="hljs-keyword">use</span> SmallNumber::*;
<span class="hljs-keyword">let</span> nums = <span class="hljs-built_in">vec!</span>[Zero, One, Two, Three];
<span class="hljs-comment">// Prints [0,1,2,3]</span>
<span class="hljs-built_in">println!</span>(<span class="hljs-string">"{}"</span>, serde_json::to_string(&nums).unwrap());
<span class="hljs-built_in">assert_eq!</span>(Two, serde_json::from_str(<span class="hljs-string">"2"</span>).unwrap());
}
</code></pre>
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