Rust 1.45.0 已发布。此版本有两个值得关注的变化：一是修复将大浮点数转换为小整数时出现的 undefined behavior 问题，官方将这种情况称为 unsoundness；二是在 expression, patterns 和 statement 中使用函数式过程宏(procedural macros)的功能已处于稳定阶段。
修复浮点数转换为整数时的 unsoundness
对于此问题，官方的解决方案是为as关键字执行"saturating cast"。下面的例子解释了什么叫 saturating cast。
fn cast(x: f32) -> u8 {
x as u8
}
fn main() {
let too_big = 300.0;
let too_small = -100.0;
let nan = f32::NAN;
println!("too_big_casted = {}", cast(too_big));
println!("too_small_casted = {}", cast(too_small));
println!("not_a_number_casted = {}", cast(nan));
}
上面的代码打印出
too_big_casted = 255
too_small_casted = 0
not_a_number_casted = 0
或者使用采用 unsafe 方式的新 API 进行转换：
let x: f32 = 1.0;
let y: u8 = unsafe { x.to_int_unchecked() };
稳定在 expression, patterns 和 statement 中使用函数式过程宏的功能
Rust 1.45.0 在三个新地方增加了调用过程宏的功能：
// imagine we have a procedural macro named "mac"
mac!(); // item position, this was what was stable before
// but these three are new:
fn main() {
let expr = mac!(); // expression position
match expr {
mac!() => {} // pattern position
}
mac!(); // statement position
}
库变更
在 Rust 1.45.0 中，以下 API 已处于稳定阶段：
此外还增加了char with ranges 来迭代代码点(codepoint)：
for ch in 'a'..='z' {
print!("{}", ch);
}
println!();
// Prints "abcdefghijklmnopqrstuvwxyz"
详情查看 https://blog.rust-lang.org/2020/07/16/Rust-1.45.0.html
