This repo tries to assess Rust string types.

We currently compare:

Name	Size	Heap	Inline	&'static str	Mutable	Unsafe	Notes
String	24 bytes	Y	-	N	Y	-	Universal
Cow<'static, str>	24 bytes	Y	-	Y	N	-
arcstr	8 bytes	?	?	?	?	?	?
cold-string	8 bytes	Y	8 bytes	N	N	Y (miri, proptest)	Space optimized for non-inline strings, 1 byte aligned (1 byte extra for Option<_>)
compact_str	24 bytes	Y	24 bytes	Y	Y	Y (miri, proptest, fuzz)	Space optimized for Option<_>
ecow	16 bytes	Y	15 bytes	N	Y	Y (miri)	O(1) clone unless mutated, Space optimized for Option<_>
flexstr	24 bytes	Y	22 bytes	Y	N	Y (miri)	O(1) clone
hipstr	24 bytes	Y	23 bytes	Y	Y	Y (miri)	O(1) clone, O(1) substring
imstr	24 bytes	?	?	?	?	?	?
kstring	24 bytes	Y	15 bytes	Y	N	Optional (miri, proptest)	Optional O(1) clone, optional 22 byte small string, Ref/Cow API for preserving &'static str
lean_string	16 bytes	Y	16 bytes	Y	Y	Y (miri, proptest)	O(1) clone unless mutated, Space optimized for Option<_>
smartstring	24 bytes	Y	23 bytes	N	Y	Y (miri, proptest, fuzz)

Suggestions:

• Generally, String
• If you deal mostly with string literals but want some flexibility (like clap), generally you'll want Cow<'static, str>
• If a profiler says your strings are a problem:
  • Try different crates and settings for that crate out with a profiler
  • O(1) clones are important when doing a lot of clones. For one-off allocations, they are slower.
  • For short-lived programs, look into string interning

Note: smol_str was removed in favor of ecow

Terms:

• Heap: will store strings in heap-allocated memory
• Inline: will store small-enough strings on the stack

Results

new summary:

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clone summary:

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access summary:

(smartstring is skipped due to how slow it is)

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self_eq summary:

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Special Thanks

• djc for inspiration with template-benchmarks-rs