#heap-allocation #rc #collect #arc #needing #trying #iterator-item-t

collect_into_rc_slice

A crate that let’s you collect an Iterator<Item=T> into an Rc<[T]> or Arc<[T]> without needing to make 2 heap allocations

1 stable release

1.0.0 Aug 2, 2023

#682 in Memory management

MIT license

23KB
371 lines

collect_into_rc_slice

A crate that let's you collect an Iterator<Item=T> into an Rc<[T]> or Arc<[T]> without needing to make 2 heap allocations.

Important Note

Please DO NOT use this if you already have a Vec<T>, sString or &[T] that contains the exact block memory you are trying convert to Rc<[T]>.

It wouldn't do anything better than the std implementation. It always better to use .into() in this case.

For example

use std::rc::Rc;

let v = vec![1,2,3];
let rc: Rc<[i32]> = v.into(); // Just use .into()

The Problem

You just learned about how cool using Rc<[T]> can be and you have an Iterator<Item=char> and you want to collect it to Rc<str>

One could naively do it as:

use std::rc::Rc;

let iter = "Hello, world!".chars();
let rc: Rc<str>  = iter.collect::<String>().into();

Which makes 2 seperate heap allocations, one for String and another one for Rc

Solution

It is very possible to do this with only 1 heap allocation, however it requires the usage of unsafe code, and good knowledge of the internal data structure of the smart pointers

With this crate you can avoid another heap allocation:

use collect_into_rc_slice::*;
use std::rc::Rc;

let iter = "Hello, world!".chars(); // Some iterator
let rc: Rc<str>  = iter.collect_into_rc_str();

Safety

This crate utilizes unsafe code to create a safe abstraction. To ensure that it is safe, it is tested, and uses miri to identify possible undefined behavior

No runtime deps