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// 或者
// 或者
*hmap.entry("key").or_insert(42) += 10;
*hmap.entry("key").or_insert(42) += 10;
</syntaxhighlight>
== 代码片段 ==
=== 将某些不满足要求的 <code>Ok</code> 转化为 <code>Err</code> ===
<syntaxhighlight lang=rust>
/// Turns into an `Err(anyhow::Error)` some `Ok`s that meet the predicate
trait AdjustResult<T, E> {
fn adjust(self, predicate: impl Fn(&T) -> bool, msg: &str) -> Result<T>
where
E: Into<anyhow::Error>;
}
impl<T, E> AdjustResult<T, E> for Result<T, E> {
fn adjust(self, predicate: impl Fn(&T) -> bool, msg: &str) -> Result<T>
where
E: Into<anyhow::Error>,
{
match self {
Ok(o) if predicate(&o) => Err(anyhow!(msg.to_string())),
Ok(o) => Ok(o),
Err(e) => Err(e.into()),
}
}
}
</syntaxhighlight>
</syntaxhighlight>