Function lending_iterator::lending_iterator::constructors::from_fn

source · [−]
pub fn from_fn<Item, State, Next>(
    state: State,
    next: Next
) -> FromFn<Item, State, Next>ⓘNotable traits for FromFn<Item, State, Next>impl<'next, Item, State, Next> LendingIteratorඞItem<'next, &'next FromFn<Item, State, Next>> for FromFn<Item, State, Next> where
    Item: HKT,
    Next: FnMut(&mut State) -> Option<Feed<'_, Item>>,     type T = Feed<'next, Item>; where
    Item: HKT,
    Next: FnMut(&mut State) -> Option<Feed<'_, Item>>, 
Expand description

Main ad-hoc / closure-based constructor of LendingIterators.

It expects the both necessary and sufficient elements for such an impl:

  • a State, which will play a role akin to that of Self in a manual impl;

  • a fn next “method” on it. There is actually a certain level of flexibility gained from this being a closure rather than a stateless associated function.

    For instance, non-lent state (such as an internal mutable counter) can be implicity captured by such a closure, without having to funnel it through the lendable State.

It can also be viewed as a convenience layer over:

::lending_iterator::repeat_mut(state)
.filter_map::<Item, _>(move |[], it| next(it))

The returned struct can also be used directly, to benefit from “named arguments”, at the cost of having to provide a PhantomData parameter.