将i128转换为f64的正确方法是什么

没有标准 f64::try_from(i128) .
您可以在互惠后通过检查来实现自己的功能 as 胁迫。

fn try_to_f64(v: i128) -> Result<f64, &'static str> {
    let attempt = v as f64;
    (attempt as i128 == v)
        .then_some(attempt)
        .ok_or("precision loss in i128 to f64 conversion")
}

fn main() {
    for v in [
        123_456_789,
        123_456_789_123,
        123_456_789_123_456,
        123_456_789_123_456_789,
    ] {
        println!("{} ~~> {:?}", v, try_to_f64(v));
    }
}
/*
123456789 ~~> Ok(123456789.0)
123456789123 ~~> Ok(123456789123.0)
123456789123456 ~~> Ok(123456789123456.0)
123456789123456789 ~~> Err("precision loss in i128 to f64 conversion")
*/