rust - 信任:隐式地从usize转换为相应的int类型

Question

我想知道是否有人有解决方案允许从usize类型(从访问数组索引或获取矢量长度中获得)的隐式转换为i32？可能吗？
当然，我假设矢量长度和数组范围在i32限制之内。

Answer 1

您可以在函数参数中使用 TryInto 特性从调用者的角度进行隐式转换。它仍然涉及转换，但是它将复杂性移到了要调用的函数上:

use std::convert::TryInto;

fn stuff(val: impl TryInto<i32>) {
    // use try_into trait method
    let val = match val.try_into() {
        Ok(v) => v,
        Err(_) => panic!("couldn't fit in i32"),
    };
    println!("in stuff: val has {} leading zeros", val.leading_zeros());
}

fn main() {
    let letters = ['a', 'b', 'c'];
    let len = letters.len();
    println!("in main: len has {} leading zeros", len.leading_zeros());
    stuff(len); // implict conversion
}

输出

in main: len has 62 leading zeros
in stuff: val has 30 leading zeros

Try on the playground