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use serde::Deserialize;

#[derive(Deserialize)]
#[serde(untagged)]
enum MaybeHelper<T> {
    Some(T),
    None(serde::de::IgnoredAny),
}

/// Something that may be an `T`.
///
/// Unlike `Option<T>`, this places no restriction on whether something
/// can't be something else entirely.
///
/// Can only be used with self-describing formats, like JSON.
#[derive(Deserialize)]
#[serde(from = "Option<MaybeHelper<T>>")]
#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[repr(transparent)]
pub struct MayBe<T>(pub Option<T>);

impl<T> Default for MayBe<T> {
    fn default() -> Self {
        Self(Default::default())
    }
}

impl<T> std::ops::Deref for MayBe<T> {
    type Target = Option<T>;
    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

impl<T> std::ops::DerefMut for MayBe<T> {
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.0
    }
}

impl<T> From<MayBe<T>> for Option<T> {
    fn from(thing: MayBe<T>) -> Option<T> {
        thing.0
    }
}

impl<T> From<Option<T>> for MayBe<T> {
    fn from(thing: Option<T>) -> MayBe<T> {
        Self(thing)
    }
}

impl<T> From<Option<MaybeHelper<T>>> for MayBe<T> {
    fn from(thing: Option<MaybeHelper<T>>) -> MayBe<T> {
        Self(match thing {
            Some(MaybeHelper::Some(v)) => Some(v),
            _ => None,
        })
    }
}