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Showing content from https://doc.rust-lang.org/std/str/trait.FromStr.html below:

FromStr in std::str - Rust

pub trait FromStr: Sized {
    type Err;

    // Required method
    fn from_str(s: &str) -> Result<Self, Self::Err>;
}

Parse a value from a string

FromStr’s from_str method is often used implicitly, through str’s parse method. See parse’s documentation for examples.

FromStr does not have a lifetime parameter, and so you can only parse types that do not contain a lifetime parameter themselves. In other words, you can parse an i32 with FromStr, but not a &i32. You can parse a struct that contains an i32, but not one that contains an &i32.

The input format expected by a type’s FromStr implementation depends on the type. Check the type’s documentation for the input formats it knows how to parse. Note that the input format of a type’s FromStr implementation might not necessarily accept the output format of its Display implementation, and even if it does, the Display implementation may not be lossless so the round-trip may lose information.

However, if a type has a lossless Display implementation whose output is meant to be conveniently machine-parseable and not just meant for human consumption, then the type may wish to accept the same format in FromStr, and document that usage. Having both Display and FromStr implementations where the result of Display cannot be parsed with FromStr may surprise users.

Basic implementation of FromStr on an example Point type:

use std::str::FromStr;

#[derive(Debug, PartialEq)]
struct Point {
    x: i32,
    y: i32
}

#[derive(Debug, PartialEq, Eq)]
struct ParsePointError;

impl FromStr for Point {
    type Err = ParsePointError;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        let (x, y) = s
            .strip_prefix('(')
            .and_then(|s| s.strip_suffix(')'))
            .and_then(|s| s.split_once(','))
            .ok_or(ParsePointError)?;

        let x_fromstr = x.parse::<i32>().map_err(|_| ParsePointError)?;
        let y_fromstr = y.parse::<i32>().map_err(|_| ParsePointError)?;

        Ok(Point { x: x_fromstr, y: y_fromstr })
    }
}

let expected = Ok(Point { x: 1, y: 2 });
assert_eq!(Point::from_str("(1,2)"), expected);
assert_eq!("(1,2)".parse(), expected);
assert_eq!("(1,2)".parse::<Point>(), expected);
assert!(Point::from_str("(1 2)").is_err());

The associated error which can be returned from parsing.

Parses a string s to return a value of this type.

If parsing succeeds, return the value inside Ok, otherwise when the string is ill-formatted return an error specific to the inside Err. The error type is specific to the implementation of the trait.

Basic usage with i32, a type that implements FromStr:

use std::str::FromStr;

let s = "5";
let x = i32::from_str(s).unwrap();

assert_eq!(5, x);

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

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