Expand description
writeable
is a utility crate of the ICU4X
project.
It includes Writeable
, a core 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.
§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<'_>);
Modules§
- Helper types for trait impls.
Macros§
- Testing macros for types implementing
TryWriteable
. - Testing macros for types implementing
Writeable
. - See
assert_writeable_eq
.
Structs§
- A hint to help consumers of
Writeable
pre-allocate bytes before they callwrite_to
. Part
s are used as annotations for formatted strings. For example, a string likeAlice, Bob
could assign aNAME
part to the substringsAlice
andBob
, and aPUNCTUATION
part to,
. This allows for example to apply styling only to names.
Traits§
- A sink that supports annotating parts of the string with
Part
s. - A writeable object that can fail while writing.
Writeable
is an alternative tostd::fmt::Display
with the addition of a length function.