Trait FromStr

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1.0.0 · Source

pub(crate) trait FromStr: Sized {
    type Err;

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

Expand description

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.

§Examples

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 });
// Explicit call
assert_eq!(Point::from_str("(1,2)"), expected);
// Implicit calls, through parse
assert_eq!("(1,2)".parse(), expected);
assert_eq!("(1,2)".parse::<Point>(), expected);
// Invalid input string
assert!(Point::from_str("(1 2)").is_err());

Required Associated Types§

1.0.0 · Source

type Err

The associated error which can be returned from parsing.

Required Methods§

1.0.0 · Source

fn from_str(s: &str) -> Result<Self, Self::Err>

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.

§Examples

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);

Dyn Compatibility§

This trait is not dyn compatible.

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

Trait FromStrCopy item path

§Examples

Required Associated Types§

type Err

Required Methods§

fn from_str(s: &str) -> Result<Self, Self::Err>

§Examples

Dyn Compatibility§

Implementors§

impl FromStr for RelayPlatform

type Err = Error

impl FromStr for RelayFamilyId

type Err = Error

impl FromStr for IptKeyRole

type Err = ParseError

impl FromStr for IpAddr

type Err = AddrParseError

impl FromStr for core::net::socket_addr::SocketAddr

type Err = AddrParseError

impl FromStr for log::Level

type Err = ParseLevelError

impl FromStr for log::LevelFilter

type Err = ParseLevelError

impl FromStr for serde_json::value::Value

type Err = Error

impl FromStr for bool

type Err = ParseBoolError

impl FromStr for char

type Err = ParseCharError

impl FromStr for f16

type Err = ParseFloatError

impl FromStr for f32

type Err = ParseFloatError

impl FromStr for f64

type Err = ParseFloatError

impl FromStr for i8

type Err = ParseIntError

impl FromStr for i16

type Err = ParseIntError

impl FromStr for i32

type Err = ParseIntError

impl FromStr for i64

type Err = ParseIntError

impl FromStr for i128

type Err = ParseIntError

impl FromStr for isize

type Err = ParseIntError

impl FromStr for u8

type Err = ParseIntError

impl FromStr for u16

type Err = ParseIntError

impl FromStr for u32

type Err = ParseIntError

impl FromStr for u64

type Err = ParseIntError

impl FromStr for u128

type Err = ParseIntError

impl FromStr for usize

type Err = ParseIntError

impl FromStr for CfgAddr

type Err = AddrParseError

impl FromStr for BridgeConfig

type Err = BridgeParseError

impl FromStr for BridgeConfigBuilder

type Err = BridgeParseError

impl FromStr for RelayFlags

type Err = Void

impl FromStr for RelayFamily

type Err = Error

impl FromStr for Nickname

type Err = Error

impl FromStr for AddrPortPattern

type Err = PolicyError

impl FromStr for PortPolicy

type Err = PolicyError

impl FromStr for PortRange

type Err = PolicyError

impl FromStr for TorVersion

type Err = Error

impl FromStr for HsClientNickname

Trait FromStr