iter-builder 0.1.0

Iterator builder with chain calls
Documentation 
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use crate::{Meta, No};

pub trait IterBase<S> {
    type T;
}
pub trait IterNext<S>: IterBase<S> {
    fn iter_next(&mut self, state: &mut S) -> Option<Self::T>;
}
pub trait IterNth<S>: IterBase<S> {
    fn iter_nth(
        &mut self,
        state: &mut S,
        next: &mut impl IterNext<S, T = Self::T>,
        n: usize,
    ) -> Option<Self::T>;
}
pub trait IterSizeHint<S>: IterBase<S> {
    fn iter_size_hint(&self, state: &S) -> (usize, Option<usize>);
}
pub trait IterNextBack<S>: IterBase<S> {
    fn iter_next_back(&mut self, state: &mut S) -> Option<Self::T>;
}
pub trait IterNthBack<S>: IterBase<S> {
    fn iter_nth_back(
        &mut self,
        state: &mut S,
        next_back: &mut impl IterNextBack<S, T = Self::T>,
        n: usize,
    ) -> Option<Self::T>;
}

pub struct Predicate<const C: bool>;
pub trait Implemented {}
pub trait Unimplemented {}

impl<F, S, T> Implemented for Meta<F, S, T> { }
impl<T> Unimplemented for No<T> { }
impl Implemented for Predicate<true> { }
impl Unimplemented for Predicate<false> { }

impl<T, S> IterBase<S> for No<T> {
    type T = T;
}
impl<T, S> IterNext<S> for No<T> {
    #[inline]
    fn iter_next(&mut self, _state: &mut S) -> Option<Self::T> {
        None
    }
}
impl<T, S> IterNth<S> for No<T> {
    #[inline]
    fn iter_nth(
        &mut self,
        state: &mut S,
        next: &mut impl IterNext<S, T = Self::T>,
        n: usize,
    ) -> Option<Self::T> {
        for _ in 0..n {
            next.iter_next(state)?;
        }
        next.iter_next(state)
    }
}
impl<T, S> IterSizeHint<S> for No<T> {
    #[inline]
    fn iter_size_hint(&self, _state: &S) -> (usize, Option<usize>) {
        (0, None)
    }
}
impl<T, S> IterNthBack<S> for No<T> {
    #[inline]
    fn iter_nth_back(
        &mut self,
        state: &mut S,
        next_back: &mut impl IterNextBack<S, T = Self::T>,
        n: usize,
    ) -> Option<Self::T> {
        for _ in 0..n {
            next_back.iter_next_back(state)?;
        }
        next_back.iter_next_back(state)
    }
}
impl<F, S, T> IterBase<S> for Meta<F, S, T> {
    type T = T;
}
impl<F: FnMut(&mut S) -> Option<T>, S, T> IterNext<S> for Meta<F, S, T> {
    #[inline]
    fn iter_next(&mut self, state: &mut S) -> Option<Self::T> {
        (self.0)(state)
    }
}
impl<F: FnMut(&mut S, usize) -> Option<T>, S, T> IterNth<S> for Meta<F, S, T> {
    #[inline]
    fn iter_nth(
        &mut self,
        state: &mut S,
        _next: &mut impl IterNext<S, T = Self::T>,
        n: usize,
    ) -> Option<Self::T> {
        (self.0)(state, n)
    }
}
impl<F: Fn(&S) -> (usize, Option<usize>), S, T> IterSizeHint<S> for Meta<F, S, T> {
    #[inline]
    fn iter_size_hint(&self, state: &S) -> (usize, Option<usize>) {
        (self.0)(state)
    }
}
impl<F: FnMut(&mut S) -> Option<T>, S, T> IterNextBack<S> for Meta<F, S, T> {
    #[inline]
    fn iter_next_back(&mut self, state: &mut S) -> Option<Self::T> {
        (self.0)(state)
    }
}
impl<F: FnMut(&mut S, usize) -> Option<T>, S, T> IterNthBack<S> for Meta<F, S, T> {
    #[inline]
    fn iter_nth_back(
        &mut self,
        state: &mut S,
        _next_back: &mut impl IterNextBack<S, T = Self::T>,
        n: usize,
    ) -> Option<Self::T> {
        (self.0)(state, n)
    }
}