Some str methods
perform destructive transformations and so they allocate, copy into and
return a new
String even
when no modification is necessary.
This crate provides a helper trait CowUtils with drop-in variants of
such methods, which behave in the same way, but avoid extra copies and
allocations when no modification is necessary.
For now it's only implemented for &str and returns
std::borrow::Cow<str>,
but in the future might be extended to other types where even more
efficient handling is possible (e.g. in-place modifications on mutable
strings).
The primary motivation for this crate was ability to perform zero-alloc replacements when no match is found, so showing results only for .replace vs .cow_replace for now.
The actual results will vary depending on the inputs, but here is a taster based on "a".repeat(40) as an input and various modes (nothing matched, everything matched and replaced, everything matched from the start and deleted):
| params | .replace (ns) | .cow_replace (ns) | difference (%) |
|---|---|---|---|
| ("a", "") | 408.59 | 290.27 | -29 |
| ("b", "c") | 98.78 | 54.00 | -45 |
| ("a", "b") | 985.99 | 1,000.70 | +1 |
First, you need to import CowUtils into the scope:
use cow_utils::CowUtils;Then you can start invoking following .cow_-prefixed methods on
strings instead of the regular ones:
.cow_replaceinstead ofstr::replace.cow_replaceninstead ofstr::replacen.cow_to_ascii_lowercaseinstead ofstr::to_ascii_lowercase.cow_to_ascii_uppercaseinstead ofstr::to_ascii_uppercase.cow_to_lowercaseinstead ofstr::to_lowercase.cow_to_uppercaseinstead ofstr::to_uppercase
Check out the docs for detailed examples.