//! An alternative to `Iterable` in many languages, a [Fn] that returns an
//! iterator.

use std::rc::Rc;

use trait_set::trait_set;

use super::boxed_iter::BoxedIter;

trait_set! {
	trait Payload<'a, T> = Fn() -> BoxedIter<'a, T> + 'a;
}

/// Dynamic iterator building callback. Given how many trait objects this
/// involves, it may actually be slower than C#.
pub struct Sequence<'a, T: 'a>(Rc<dyn Payload<'a, T>>);
impl<'a, T: 'a> Sequence<'a, T> {
	/// Construct from a concrete function returning a concrete iterator
	pub fn new<I: IntoIterator<Item = T> + 'a>(f: impl Fn() -> I + 'a) -> Self {
		Self(Rc::new(move || Box::new(f().into_iter())))
	}
	/// Get an iterator from the function
	pub fn iter(&self) -> BoxedIter<'_, T> { (self.0)() }
}
impl<'a, T: 'a> Clone for Sequence<'a, T> {
	fn clone(&self) -> Self { Self(self.0.clone()) }
}