#stack-memory #heap-allocation #memory #inline #stack #string #vector

nightly inlined

Types for inlining small collections for avoiding unnecessary heap allocations

1 unstable release

0.1.1 Mar 27, 2024
0.1.0 Mar 26, 2024

#550 in Memory management

21 downloads per month
Used in portal-tunneler

MIT/Apache

81KB
2K SLoC

Types for inlining small collections for avoiding unnecessary heap allocations.

It is common to need to use a vector to store a few small elements and end up using a [Vec]. This type allocates memory on the heap, and if you're only using a few elements then it is more efficient to use the stack, or inline the vector into whatever structure you're operating on.

For example, domain names are typically less than 100 characters and cannot be over 255. Instead of using String, that allocates memory on the heap both on creation and on clone, you can use a TinyString::<255>, a 256-byte structure that can store up to 255 bytes using inline memory, and cloning is as simple as copying memory:

use inlined::TinyString;
use std::fmt::Write;

let mut s = TinyString::<32>::new(); // 32 is the maximum length of the string

s.push_str("Hello!");
assert_eq!(s.as_str(), "Hello!");

let _ = write!(s, " Your number is {}.", 1234);
assert_eq!(s.as_str(), "Hello! Your number is 1234.")

Provided types

This crate contains the following types:

  • The InlineVec and InlineString types are analogous to [Vec] and String from the standard library, but are inlined and have a constant, limited capacity.
  • The TinyVec and TinyString types work much the same way, but use an u8 for the length instead of an usize. This makes them more optimal for passing around, or inlining them into other structs.
  • The CompactVec is a type that brings together [Vec] and TinyVec, representing a vector that stores up to N elements inline, but if more capacity is needed will spill into the heap and allocate memory.

Since all of these implement Deref for either &[T] or &str, they contain many of the methods you're used to having from [Vec] and String.

Specifying the capacity

All these types make use of const generics to specify their inline capacity. This means you can choose the maximum amount of elements you want your inlined type to store. Whether you want to store just 3, 100, or even thousands of elements, the same types have got you covered.

No runtime deps