mirror of
https://github.com/bspeice/speice.io
synced 2025-10-31 01:20:31 -04:00
34 lines
1.6 KiB
Markdown
34 lines
1.6 KiB
Markdown
---
|
|
layout: post
|
|
title: "Summary: What Are the Rules?"
|
|
description: "A synopsis and reference."
|
|
category:
|
|
tags: [rust, understanding-allocations]
|
|
---
|
|
|
|
While there's a lot of interesting detail captured in this series, it's often helpful
|
|
to have a document that answers some "yes/no" questions. You may not care about
|
|
what an `Iterator` looks like in assembly, you just need to know whether it allocates
|
|
an object on the heap or not. And while Rust will prioritize the fastest behavior it can,
|
|
here are the rules for each memory type:
|
|
|
|
**Heap Allocation**:
|
|
- Smart pointers (`Box`, `Rc`, `Mutex`, etc.) allocate their contents in heap memory.
|
|
- Collections (`HashMap`, `Vec`, `String`, etc.) allocate their contents in heap memory.
|
|
- Some smart pointers in the standard library have counterparts in other crates that
|
|
don't need heap memory. If possible, use those.
|
|
|
|
**Stack Allocation**:
|
|
- Everything not using a smart pointer will be allocated on the stack.
|
|
- Structs, enums, iterators, arrays, and closures are all stack allocated.
|
|
- Cell types (`RefCell`) behave like smart pointers, but are stack-allocated.
|
|
- Inlining (`#[inline]`) will not affect allocation behavior for better or worse.
|
|
- Types that are marked `Copy` are guaranteed to have their contents stack-allocated.
|
|
|
|
**Global Allocation**:
|
|
- `const` is a fixed value; the compiler is allowed to copy it wherever useful.
|
|
- `static` is a fixed reference; the compiler will guarantee it is unique.
|
|
|
|
|
|
-- [Raph Levien](https://docs.google.com/presentation/d/1q-c7UAyrUlM-eZyTo1pd8SZ0qwA_wYxmPZVOQkoDmH4/edit?usp=sharing)
|