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//! Contains the [DropTrigger] type.

/// Calls a closure when it's dropped, unless it's disarmed first.
/// This struct is useful for implementing cleanup operations.
pub struct DropTrigger<F: FnOnce()> {
    trigger: Option<F>,
}

impl<F: FnOnce()> DropTrigger<F> {
    /// Creates a [DropTrigger] which will call the given closure when dropped.
    pub fn new(trigger: F) -> Self {
        Self {
            trigger: Some(trigger),
        }
    }

    /// Disarms this [DropTrigger] so that its closure will not be called when when it's dropped.
    pub fn disarm(&mut self) -> bool {
        self.trigger.take().is_some()
    }
}

impl<F: FnOnce()> Drop for DropTrigger<F> {
    fn drop(&mut self) {
        if let Some(trigger) = self.trigger.take() {
            trigger()
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn trigger_called_on_drop() {
        let mut x = 0;
        let dt = DropTrigger::new(|| x += 1);

        drop(dt);

        assert_eq!(1, x);
    }

    #[test]
    fn trigger_not_called_when_disarmed() {
        let mut x = 0;
        let mut dt = DropTrigger::new(|| x += 1);

        let was_armed = dt.disarm();
        drop(dt);

        assert!(was_armed);
        assert_eq!(0, x);
    }

    #[test]
    fn disarm_returns_false_if_was_not_armed() {
        let mut x = 0;
        let mut dt = DropTrigger::new(|| x += 1);

        let first = dt.disarm();
        let second = dt.disarm();
        drop(dt);

        assert!(first);
        assert!(!second);
    }
}