pub 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.
§Input format and round-tripping
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.
§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§
Required Methods§
1.0.0 · Sourcefn from_str(s: &str) -> Result<Self, Self::Err>
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.
Implementors§
1.0.0 · Source§impl FromStr for SocketAddr
impl FromStr for SocketAddr
type Err = AddrParseError
Source§impl FromStr for log::LevelFilter
impl FromStr for log::LevelFilter
type Err = ParseLevelError
Source§impl FromStr for ByteString
impl FromStr for ByteString
type Err = Infallible
1.5.0 · Source§impl FromStr for SocketAddrV4
impl FromStr for SocketAddrV4
type Err = AddrParseError
1.5.0 · Source§impl FromStr for SocketAddrV6
impl FromStr for SocketAddrV6
type Err = AddrParseError
Source§impl FromStr for HeaderName
impl FromStr for HeaderName
type Err = InvalidHeaderName
Source§impl FromStr for HeaderValue
impl FromStr for HeaderValue
type Err = InvalidHeaderValue
Source§impl FromStr for StatusCode
impl FromStr for StatusCode
type Err = InvalidStatusCode
Source§impl FromStr for PathAndQuery
impl FromStr for PathAndQuery
type Err = InvalidUri
Source§impl FromStr for icu_locale_core::extensions::private::other::Subtag
impl FromStr for icu_locale_core::extensions::private::other::Subtag
type Err = ParseError
Source§impl FromStr for icu_locale_core::extensions::transform::key::Key
impl FromStr for icu_locale_core::extensions::transform::key::Key
type Err = ParseError
Source§impl FromStr for SubdivisionId
impl FromStr for SubdivisionId
type Err = ParseError
Source§impl FromStr for SubdivisionSuffix
impl FromStr for SubdivisionSuffix
type Err = ParseError
Source§impl FromStr for Affine<EdwardsParameters>
impl FromStr for Affine<EdwardsParameters>
type Err = GroupError
Source§impl FromStr for tracing_core::metadata::LevelFilter
impl FromStr for tracing_core::metadata::LevelFilter
type Err = ParseLevelFilterError
Source§impl FromStr for Url
Parse a string as an URL, without a base URL or encoding override.
impl FromStr for Url
Parse a string as an URL, without a base URL or encoding override.