Crate smallvec[−][src]

Expand description

Small vectors in various sizes. These store a certain number of elements inline, and fall back to the heap for larger allocations. This can be a useful optimization for improving cache locality and reducing allocator traffic for workloads that fit within the inline buffer.

`no_std` support

By default, smallvec does not depend on std. However, the optional write feature implements the std::io::Write trait for vectors of u8. When this feature is enabled, smallvec depends on std.

Optional features

`serde`

When this optional dependency is enabled, SmallVec implements the serde::Serialize and serde::Deserialize traits.

`write`

When this feature is enabled, SmallVec<[u8; _]> implements the std::io::Write trait. This feature is not compatible with #![no_std] programs.

`union`

This feature requires Rust 1.49.

When the union feature is enabled smallvec will track its state (inline or spilled) without the use of an enum tag, reducing the size of the smallvec by one machine word. This means that there is potentially no space overhead compared to Vec. Note that smallvec can still be larger than Vec if the inline buffer is larger than two machine words.

To use this feature add features = ["union"] in the smallvec section of Cargo.toml. Note that this feature requires Rust 1.49.

Tracking issue: rust-lang/rust#55149

`const_generics`

This feature is unstable and requires a nightly build of the Rust toolchain.

When this feature is enabled, SmallVec works with any arrays of any size, not just a fixed list of sizes.

Tracking issue: rust-lang/rust#44580

`specialization`

This feature is unstable and requires a nightly build of the Rust toolchain.

When this feature is enabled, SmallVec::from(slice) has improved performance for slices of Copy types. (Without this feature, you can use SmallVec::from_slice to get optimal performance for Copy types.)

Tracking issue: rust-lang/rust#31844