TryFrom and TryInto - The Edition Guide

# TryFrom and TryInto

Initially added:

The `TryFrom` and `TryInto` traits are like the `From` and `Into` traits, except that they return a result, meaning that they may fail.

For example, the `from_be_bytes` and related methods on integer types take arrays, but data is often read in via slices. Converting between slices and arrays is tedious to do manually. With the new traits, it can be done inline with `.try_into()`:

    use std::convert::TryInto;
    fn main() -> Result<(), Box<dyn std::error::Error>> {
    let slice = &[1, 2, 3, 4][..];
    let num = u32::from_be_bytes(slice.try_into()?);
    Ok(())
    }