efd 10.1.3

1D/2D/3D Elliptical Fourier Descriptor (EFD) implementation in Rust.
Documentation 
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use alloc::{borrow::Cow, vec::Vec};

pub(crate) type MatrixRxX<const D: usize> = na::OMatrix<f64, na::Const<D>, na::Dyn>;

pub(crate) fn to_mat<C, const D: usize>(curve: C) -> MatrixRxX<D>
where
    C: Curve<D>,
{
    MatrixRxX::from_iterator(curve.len(), curve.as_curve().iter().flatten().copied())
}

/// Copy-on-write curve type.
///
/// Instead of using [`alloc::borrow::Cow`] with a slice type `[[f64; D]]`, this
/// trait does not require any type conversion.
pub trait Curve<const D: usize>: Sized {
    /// Move or copy curve type into the owned type [`Vec`].
    fn to_curve(self) -> Vec<[f64; D]>;

    /// Elements view.
    fn as_curve(&self) -> &[[f64; D]];

    /// Length of the curve.
    fn len(&self) -> usize {
        self.as_curve().len()
    }

    /// Check if the curve is empty.
    fn is_empty(&self) -> bool {
        self.as_curve().is_empty()
    }

    /// Close the curve by the first element.
    ///
    /// # Panics
    /// Panics if the curve is empty.
    fn closed_lin(self) -> Vec<[f64; D]> {
        let mut c = self.to_curve();
        c.push(c[0]);
        c
    }

    /// Remove the last element.
    fn popped_last(self) -> Vec<[f64; D]> {
        let mut curve = self.to_curve();
        curve.pop();
        curve
    }

    /// Check if a curve's first and end points are the same.
    fn is_closed(&self) -> bool {
        let curve = self.as_curve();
        curve.first() == curve.last()
    }
}

impl<const D: usize> Curve<D> for Vec<[f64; D]> {
    fn to_curve(self) -> Vec<[f64; D]> {
        self
    }

    fn as_curve(&self) -> &[[f64; D]] {
        self
    }
}

macro_rules! impl_slice {
    () => {
        fn to_curve(self) -> Vec<[f64; D]> {
            self.to_vec()
        }

        fn as_curve(&self) -> &[[f64; D]] {
            self
        }
    };
}

impl<const D: usize, const N: usize> Curve<D> for [[f64; D]; N] {
    impl_slice!();
}

impl<const D: usize> Curve<D> for &[[f64; D]] {
    impl_slice!();
}

impl<const D: usize> Curve<D> for Cow<'_, [[f64; D]]> {
    impl_slice!();
}

impl<const D: usize, T: Curve<D> + Clone> Curve<D> for &T {
    fn to_curve(self) -> Vec<[f64; D]> {
        self.clone().to_curve()
    }

    fn as_curve(&self) -> &[[f64; D]] {
        (*self).as_curve()
    }
}

impl<const D: usize> Curve<D> for core::slice::Iter<'_, [f64; D]> {
    fn to_curve(self) -> Vec<[f64; D]> {
        self.copied().collect()
    }

    fn as_curve(&self) -> &[[f64; D]] {
        self.as_slice()
    }
}

impl<const D: usize, const N: usize> Curve<D> for core::array::IntoIter<[f64; D], N> {
    fn to_curve(self) -> Vec<[f64; D]> {
        self.collect()
    }

    fn as_curve(&self) -> &[[f64; D]] {
        self.as_slice()
    }
}

impl<const D: usize> Curve<D> for alloc::vec::IntoIter<[f64; D]> {
    fn to_curve(self) -> Vec<[f64; D]> {
        self.collect()
    }

    fn as_curve(&self) -> &[[f64; D]] {
        self.as_slice()
    }
}