epserde 0.12.6

ε-serde is an ε-copy (i.e., almost zero-copy) serialization/deserialization framework
Documentation 
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/*
 * SPDX-FileCopyrightText: 2025 Sebastiano Vigna
 *
 * SPDX-License-Identifier: Apache-2.0 OR LGPL-2.1-or-later
 */

//! Implementations for exact-size iterators.
//!
//! In theory all types serialized by ε-serde must be immutable. However, we
//! provide a convenience implementation that serializes [exact-size
//! iterators](core::iter::ExactSizeIterator) returning elements that
//! are [`Borrow<T>`](core::borrow::Borrow) for some type `T` as
//! vectors of `T`.
//!
//! More precisely, we provide a [`SerIter`] type that [wraps](SerIter::new) an
//! iterator into a serializable type. We provide a [`From`] implementation for
//! convenience.
//!
//! Note, however, that you must deserialize the iterator as a vector—see the
//! example in the [crate-level documentation](crate).
use core::{borrow::Borrow, cell::RefCell, ops::DerefMut};

use crate::prelude::*;
use ser::*;

#[cfg(not(feature = "std"))]
use alloc::boxed::Box;

#[derive(Clone, Debug, PartialEq, Eq, Default)]
/// A wrapper serializing an exact-size iterator as a boxed slice.
///
/// For more information, see the [module-level
/// documentation](crate::impls::iter).
pub struct SerIter<T, I: ExactSizeIterator>(RefCell<I>, core::marker::PhantomData<T>);

impl<T, I: ExactSizeIterator> SerIter<T, I> {
    pub fn new(iter: I) -> Self {
        SerIter(RefCell::new(iter), core::marker::PhantomData)
    }
}

impl<T, I: ExactSizeIterator> From<I> for SerIter<T, I> {
    fn from(iter: I) -> Self {
        SerIter::new(iter)
    }
}

impl<T, I> SerInner for SerIter<T, I>
where
    I: ExactSizeIterator,
    I::Item: Borrow<T>,
    T: CopyType + SerInner,
    Self: SerHelper<<T as CopyType>::Copy>,
{
    type SerType = Box<[T::SerType]>;
    const IS_ZERO_COPY: bool = false;
    unsafe fn _ser_inner(&self, backend: &mut impl WriteWithNames) -> ser::Result<()> {
        unsafe { <Self as SerHelper<<T as CopyType>::Copy>>::_ser_inner(self, backend) }
    }
}

impl<T, I> SerHelper<Zero> for SerIter<T, I>
where
    I: ExactSizeIterator,
    I::Item: Borrow<T>,
    T: ZeroCopy,
{
    unsafe fn _ser_inner(&self, backend: &mut impl WriteWithNames) -> ser::Result<()> {
        check_zero_copy::<T>();
        let mut iter = self.0.borrow_mut();
        let len = iter.len();
        backend.write("len", &len)?;
        backend.align::<T>()?;

        let mut c = 0;
        for item in iter.deref_mut() {
            ser_zero_unchecked(backend, item.borrow())?;
            c += 1;
        }

        if c != len {
            Err(ser::Error::IteratorLengthMismatch {
                actual: c,
                expected: len,
            })
        } else {
            Ok(())
        }
    }
}

impl<T, I> SerHelper<Deep> for SerIter<T, I>
where
    I: ExactSizeIterator,
    I::Item: Borrow<T>,
    T: DeepCopy,
{
    unsafe fn _ser_inner(&self, backend: &mut impl WriteWithNames) -> ser::Result<()> {
        let mut iter = self.0.borrow_mut();
        let len = iter.len();
        backend.write("len", &len)?;

        let mut c = 0;
        for item in iter.deref_mut() {
            unsafe { item.borrow()._ser_inner(backend)? };
            c += 1;
        }

        if c != len {
            Err(ser::Error::IteratorLengthMismatch {
                actual: c,
                expected: len,
            })
        } else {
            Ok(())
        }
    }
}