in midst of refactor

orchid-base/src/sequence.rs

@@ -0,0 +1,27 @@
+//! 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) -> impl Iterator<Item = T> + '_ { (self.0)() }
+}
+impl<'a, T: 'a> Clone for Sequence<'a, T> {
+  fn clone(&self) -> Self { Self(self.0.clone()) }
+}