inlinable_string

The inlinable_string crate provides the InlinableString type — an owned, grow-able UTF-8 string that stores small strings inline and avoids heap-allocation — and the StringExt trait which abstracts string operations over both std::string::String and InlinableString (or even your own custom string type).

StringExt's API is mostly identical to std::string::String; unstable and deprecated methods are not included. A StringExt implementation is provided for both std::string::String and InlinableString. This enables InlinableString to generally work as a drop-in replacement for std::string::String and &StringExt to work with references to either type.

But is it actually faster than using std::string::String?

Here are some current (micro)benchmark results. I encourage you to verify them yourself by running cargo bench --feature nightly with a nightly Rust! I am also very open to adding more realistic and representative benchmarks! Share some ideas with me!

Constructing from a large &str:

test benches::bench_inlinable_string_from_large                ... bench:          32 ns/iter (+/- 6)
test benches::bench_std_string_from_large                      ... bench:          31 ns/iter (+/- 10)

Constructing from a small &str:

test benches::bench_inlinable_string_from_small                ... bench:           1 ns/iter (+/- 0)
test benches::bench_std_string_from_small                      ... bench:          26 ns/iter (+/- 14)

Pushing a large &str onto an empty string:

test benches::bench_inlinable_string_push_str_large_onto_empty ... bench:          37 ns/iter (+/- 12)
test benches::bench_std_string_push_str_large_onto_empty       ... bench:          30 ns/iter (+/- 9)

Pushing a small &str onto an empty string:

test benches::bench_inlinable_string_push_str_small_onto_empty ... bench:          11 ns/iter (+/- 4)
test benches::bench_std_string_push_str_small_onto_empty       ... bench:          23 ns/iter (+/- 10)

Pushing a large &str onto a large string:

test benches::bench_inlinable_string_push_str_large_onto_large ... bench:          80 ns/iter (+/- 24)
test benches::bench_std_string_push_str_large_onto_large       ... bench:          78 ns/iter (+/- 23)

Pushing a small &str onto a small string:

test benches::bench_inlinable_string_push_str_small_onto_small ... bench:          17 ns/iter (+/- 6)
test benches::bench_std_string_push_str_small_onto_small       ... bench:          60 ns/iter (+/- 15)

TLDR: If your string's size tends to stay within INLINE_STRING_CAPACITY, then InlinableString is much faster. Crossing the threshold and forcing a promotion from inline storage to heap allocation will slow it down more than std::string::String and you can see the expected drop off in such cases, but that is generally a one time cost. Once the strings are already larger than INLINE_STRING_CAPACITY, then the performance difference is negligible. However, take all this with a grain of salt! These are very micro benchmarks and your (hashtag) Real World workload may differ greatly!

Install

Either

$ cargo add inlinable_string

or add this to your Cargo.toml:

[dependencies]
inlinable_string = "0.1.0"

Documentation

Documentation