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    // Unlike `impl Into<Option<T>>` or `Option<impl Into<T>>`, this isn't ambiguous for the `None`
    // case.

    use crate::builder::ArgAction;
    use crate::builder::OsStr;
    use crate::builder::Str;
    use crate::builder::StyledStr;
    use crate::builder::ValueHint;
    use crate::builder::ValueParser;
    use crate::builder::ValueRange;

    /// Clearable builder value
    ///
    /// This allows a builder function to both accept any value that can [`Into::into`] `T` (like
    /// `&str` into `OsStr`) as well as `None` to reset it to the default.  This is needed to
    /// workaround a limitation where you can't have a function argument that is `impl Into<Option<T>>`
    /// where `T` is `impl Into<S>` accept `None` as its type is ambiguous.
    ///
    /// # Example
    ///
    /// ```rust
    /// # use clap::Command;
    /// # use clap::Arg;
    /// fn common() -> Command {
    ///     Command::new("cli")
    ///         .arg(Arg::new("input").short('i').long("input"))
    /// }
    /// let mut command = common();
    /// command.mut_arg("input", |arg| arg.short(None));
    /// ```
    #[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
    pub enum Resettable<T> {
        /// Overwrite builder value
        Value(T),
        /// Reset builder value
        Reset,
    }

    impl<T> Resettable<T> {
        pub(crate) fn into_option(self) -> Option<T> {
            match self {
                Self::Value(t) => Some(t),
                Self::Reset => None,
            }
        }
    }

    impl<T> From<T> for Resettable<T> {
        fn from(other: T) -> Self {
            Self::Value(other)
        }
    }

    impl<T> From<Option<T>> for Resettable<T> {
        fn from(other: Option<T>) -> Self {
            match other {
                Some(inner) => Self::Value(inner),
                None => Self::Reset,
            }
        }
    }

    /// Convert to the intended resettable type
    pub trait IntoResettable<T> {
        /// Convert to the intended resettable type
        fn into_resettable(self) -> Resettable<T>;
    }

    impl IntoResettable<char> for Option<char> {
        fn into_resettable(self) -> Resettable<char> {
            match self {
                Some(s) => Resettable::Value(s),
                None => Resettable::Reset,
            }
        }
    }

    impl IntoResettable<usize> for Option<usize> {
        fn into_resettable(self) -> Resettable<usize> {
            match self {
                Some(s) => Resettable::Value(s),
                None => Resettable::Reset,
            }
        }
    }

    impl IntoResettable<ArgAction> for Option<ArgAction> {
        fn into_resettable(self) -> Resettable<ArgAction> {
            match self {
                Some(s) => Resettable::Value(s),
                None => Resettable::Reset,
            }
        }
    }

    impl IntoResettable<ValueHint> for Option<ValueHint> {
        fn into_resettable(self) -> Resettable<ValueHint> {
            match self {
                Some(s) => Resettable::Value(s),
                None => Resettable::Reset,
            }
        }
    }

    impl IntoResettable<ValueParser> for Option<ValueParser> {
        fn into_resettable(self) -> Resettable<ValueParser> {
            match self {
                Some(s) => Resettable::Value(s),
                None => Resettable::Reset,
            }
        }
    }

    impl IntoResettable<StyledStr> for Option<&'static str> {
        fn into_resettable(self) -> Resettable<StyledStr> {
            match self {
                Some(s) => Resettable::Value(s.into()),
                None => Resettable::Reset,
            }
        }
    }

    impl IntoResettable<OsStr> for Option<&'static str> {
        fn into_resettable(self) -> Resettable<OsStr> {
            match self {
                Some(s) => Resettable::Value(s.into()),
                None => Resettable::Reset,
            }
        }
    }

    impl IntoResettable<Str> for Option<&'static str> {
        fn into_resettable(self) -> Resettable<Str> {
            match self {
                Some(s) => Resettable::Value(s.into()),
                None => Resettable::Reset,
            }
        }
    }

    impl<T> IntoResettable<T> for Resettable<T> {
        fn into_resettable(self) -> Resettable<T> {
            self
        }
    }

    impl IntoResettable<char> for char {
        fn into_resettable(self) -> Resettable<char> {
            Resettable::Value(self)
        }
    }

    impl IntoResettable<usize> for usize {
        fn into_resettable(self) -> Resettable<usize> {
            Resettable::Value(self)
        }
    }

    impl IntoResettable<ArgAction> for ArgAction {
        fn into_resettable(self) -> Resettable<ArgAction> {
            Resettable::Value(self)
        }
    }

    impl IntoResettable<ValueHint> for ValueHint {
        fn into_resettable(self) -> Resettable<ValueHint> {
            Resettable::Value(self)
        }
    }

    impl<I: Into<ValueRange>> IntoResettable<ValueRange> for I {
        fn into_resettable(self) -> Resettable<ValueRange> {
            Resettable::Value(self.into())
        }
    }

    impl<I: Into<ValueParser>> IntoResettable<ValueParser> for I {
        fn into_resettable(self) -> Resettable<ValueParser> {
            Resettable::Value(self.into())
        }
    }

    impl<I: Into<String>> IntoResettable<String> for I {
        fn into_resettable(self) -> Resettable<String> {
            Resettable::Value(self.into())
        }
    }

    impl<I: Into<StyledStr>> IntoResettable<StyledStr> for I {
        fn into_resettable(self) -> Resettable<StyledStr> {
            Resettable::Value(self.into())
        }
    }

    impl<I: Into<OsStr>> IntoResettable<OsStr> for I {
        fn into_resettable(self) -> Resettable<OsStr> {
            Resettable::Value(self.into())
        }
    }

    impl<I: Into<Str>> IntoResettable<Str> for I {
        fn into_resettable(self) -> Resettable<Str> {
            Resettable::Value(self.into())
        }
    }

    impl<I: Into<crate::Id>> IntoResettable<crate::Id> for I {
        fn into_resettable(self) -> Resettable<crate::Id> {
            Resettable::Value(self.into())
        }
    }