bytes_to_field_elements should accept and return an iterator

[ggutoski]

Problem

Originally posted by @ggutoski in #299 (comment)

Currently bytes_to_field_elements takes AsRef<[u8]> as input and returns Vec<F> as output. This can lead to unnecessary mem copy or heap alloc if the caller doesn't already have a AsRef<[u8]> or wants the output in some form other than Vec<F>.

Example: here the caller actually wants a Vec<Vec<F>>, and needs to copy/allocate a whole 2D vec for this purpose.

https://github.com/EspressoSystems/hotshot-primitives/blob/52b2f713eea897778eb8a73f401c9b1b4a2dde19/src/vid/advz.rs#L158-L159

Solution

bytes_to_field_elements should accept IntoIterator instead of AsRef<[u8]> and should return an iterator over F instead of Vec<F>.

We should do the same for bytes_from_field_elements, though that will be more complicated to implement.

This solution is an example of the iterator adaptor pattern:

• Processing a Series of Items with Iterators - The Rust Programming Language
• std::iter - Rust

[amit0365]

Hello I am planning to work on this. Are you close to implementing the solution @ggutoski ?

[ggutoski]

Hello I am planning to work on this. Are you close to implementing the solution @ggutoski ?

Hello @amit0365 . I have spent no time on this issue. Feel free to work on it! ❤️