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.
Types implementing Writeable have a defaulted write_to_string
function. If desired, types implementing Writeable
can manually implement ToString
to wrap write_to_string
.
Examples
use writeable::Writeable;
use writeable::LengthHint;
use writeable::assert_writeable_eq;
use std::fmt;
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 write_len(&self) -> LengthHint {
// "Hello, " + '!' + length of name
LengthHint::exact(8 + self.name.len())
}
}
let message = WelcomeMessage { name: "Alice" };
assert_writeable_eq!(&message, "Hello, Alice!");
Macros
Testing macros for types implementing Writeable. The first argument should be a
Writeable
, the second argument a string, and the third argument (*_parts_eq only)
a list of parts ([(usize, usize, Part)]
).
Structs
A hint to help consumers of Writeable
pre-allocate bytes before they call
write_to
.
Traits
A sink that supports annotating parts of the string with Part
s.
Writeable
is an alternative to std::fmt::Display
with the addition of a length function.