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#[doc(hidden)]
pub struct Deferrer<F: FnOnce()> {
	function: Option<F>,
}

impl<F: FnOnce()> Deferrer<F> {
	pub fn new(f: F) -> impl Drop {
		Self { function: Some(f) }
	}
}

impl<F: FnOnce()> Drop for Deferrer<F> {
	fn drop(&mut self) {
		self.function.take().map(|f| f());
	}
}

/// Used for deferring a ``FnOnce()``. Deferred functions will called at the end of the scope.
///
/// # Example
/// ```
/// use deferrer::defer;
/// use std::cell::RefCell;
///
/// let mut s = RefCell::new(String::from("Hello"));
/// {
/// 	defer!( || s.borrow_mut().push_str(" world!") );
/// 	assert_eq!(*s.borrow(), "Hello");
/// }
/// assert_eq!(*s.borrow(), "Hello world!");
/// ```
///
#[macro_export]
macro_rules! defer {
	($func:expr) => {
		let _deferer = $crate::Deferrer::new($func);
	};
}

#[cfg(test)]
mod test {
	use std::cell::RefCell;
	use super::*;

	#[test]
	fn test_defer_function() {	
		let i = RefCell::new(0);
		{
			let _d = Deferrer::new(|| { *i.borrow_mut() = 1 });
			assert_eq!(*i.borrow(), 0);
		}
		assert_eq!(*i.borrow(), 1);
	}

	#[test]
	fn test_defer_macro() {
		let i = RefCell::new(0);
		let j = RefCell::new(0);
		{
			defer!( || {*i.borrow_mut() = 1} );
			defer!( || {*j.borrow_mut() = 1} );
			assert_eq!(*i.borrow(), 0);
			assert_eq!(*j.borrow(), 0);
		}
		assert_eq!(*i.borrow(), 1);
		assert_eq!(*j.borrow(), 1);
	}
}