writeable (0.6.2)
Published 2026-03-26 10:37:04 +00:00 by siennathesane
Installation
[registry]
default = "gitea"
[registries.gitea]
index = "sparse+cargo add writeable@0.6.2About this package
A more efficient alternative to fmt::Display
writeable 
This crate defines [Writeable], a trait representing an object that can be written to a
sink implementing std::fmt::Write. It is an alternative to std::fmt::Display with the
addition of a function indicating the number of bytes to be written.
Writeable improves upon std::fmt::Display in two ways:
- More efficient, since the sink can pre-allocate bytes.
- Smaller code, since the format machinery can be short-circuited.
This crate also exports [TryWriteable], a writeable that supports a custom error.
Benchmarks
The benchmarks to generate the following data can be found in the benches directory.
| Case | Writeable |
Display |
|---|---|---|
| Create string from single-string message (139 chars) | 15.642 ns | 19.251 ns |
| Create string from complex message | 35.830 ns | 89.478 ns |
| Write complex message to buffer | 57.336 ns | 64.408 ns |
Examples
use std::fmt;
use writeable::assert_writeable_eq;
use writeable::LengthHint;
use writeable::Writeable;
struct WelcomeMessage<'s> {
pub name: &'s str,
}
impl<'s> Writeable for WelcomeMessage<'s> {
fn write_to<W: fmt::Write + ?Sized>(&self, sink: &mut W) -> fmt::Result {
sink.write_str("Hello, ")?;
sink.write_str(self.name)?;
sink.write_char('!')?;
Ok(())
}
fn writeable_length_hint(&self) -> LengthHint {
// "Hello, " + '!' + length of name
LengthHint::exact(8 + self.name.len())
}
}
let message = WelcomeMessage { name: "Alice" };
assert_writeable_eq!(&message, "Hello, Alice!");
// Types implementing `Writeable` are recommended to also implement `fmt::Display`.
// This can be simply done by redirecting to the `Writeable` implementation:
writeable::impl_display_with_writeable!(WelcomeMessage<'_>);
assert_eq!(message.to_string(), "Hello, Alice!");
More Information
For more information on development, authorship, contributing etc. please visit ICU4X home page.
Dependencies
| ID | Version |
|---|---|
| either | ^1.9.0 |
| rand | ^0.9 |
| criterion | ^0.5.0 |