writeable

writeable 是 ICU4X 项目的实用工具包。

它包括 Writeable，这是一个核心特质，代表一个可以写入实现 std::fmt::Write 的 sink 的对象。它是 std::fmt::Display 的替代品，增加了指示要写入的字节数的函数。

Writeable 在两个方面改进了 std::fmt::Display

1. 更高效，因为 sink 可以预先分配字节。
2. 代码更少，因为格式化机制可以被短路。

示例

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<'_>);

更多信息

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