Vector with custom allocator in Rust

1 min readMar 16, 2023


I have been learning Rust! That’s true I have difficulty in learning Rust now.

They added a new feature in Rust, vec and box can support custom allocator. Please check this two flows

  • Rust allocators working group roadmap:
  • Custom allocators for Vec:

I will check the vector one today!

They added new two methods for that. new_in and with_capacity_in

They put this example…

#![feature(allocator_api)]  // it is unstable library, you should it to enable this feature

use std::alloc::System;

let mut vec: Vec<i32, _> = Vec::new_in(System);

Himm.. they need this Allocator trait!

You should implement your allocator trait.. and give it to new_in() method.

How to implement trait..

unsafe impl Allocator for SimpleAllocator {
fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
// put your own stuff there

unsafe fn deallocate(&self, _ptr: NonNull<u8>, _layout: Layout) {
// put your own stuff

allocate() and deallocate() are required method to implement Allocator trait.

I hope it helps!