Module icu_locid::shortvec

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This module includes variable-length data types that are const-constructible for single values and overflow to the heap.

§Why?

This module is far from the first stack-or-heap vector in the Rust ecosystem. It was created with the following value proposition:

  1. Enable safe const construction of stack collections.
  2. Avoid stack size penalties common with stack-or-heap collections.

As of this writing, heapless and tinyvec don’t support const construction except for empty vectors, and smallvec supports it on unstable.

Additionally, ShortBoxSlice has a smaller stack size than any of these:

ⓘ
use core::mem::size_of;

// NonZeroU64 has a niche that this module utilizes
use core::num::NonZeroU64;

// ShortBoxSlice is the same size as `Box<[]>` for small or nichey values
assert_eq!(16, size_of::<shortvec::ShortBoxSlice::<NonZeroU64>>());

// Note: SmallVec supports pushing and therefore has a capacity field
assert_eq!(24, size_of::<smallvec::SmallVec::<[NonZeroU64; 1]>>());

// Note: heapless doesn't support spilling to the heap
assert_eq!(16, size_of::<heapless::Vec::<NonZeroU64, 1>>());

// Note: TinyVec only supports types that implement `Default`
assert_eq!(24, size_of::<tinyvec::TinyVec::<[u64; 1]>>());

The module is no_std with alloc.

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