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;
use std::num::ParseIntError;
#[derive(Debug, PartialEq)]
struct Point {
x: i32,
y: i32
}
impl FromStr for Point {
type Err = ParseIntError;
fn from_str(s: &str) -> Result<Self, Self::Err> {
let coords: Vec<&str> = s.trim_matches(|p| p == '(' || p == ')' )
.split(',')
.collect();
let x_fromstr = coords[0].parse::<i32>()?;
let y_fromstr = coords[1].parse::<i32>()?;
Ok(Point { x: x_fromstr, y: y_fromstr })
}
}
let p = Point::from_str("(1,2)");
assert_eq!(p.unwrap(), Point{ x: 1, y: 2} )Associated Types
Required methods
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);Implementations on Foreign Types
1.5.0 · sourceimpl FromStr for SocketAddrV6
impl FromStr for SocketAddrV6
type Err = AddrParseError
pub fn from_str(s: &str) -> Result<SocketAddrV6, AddrParseError>
1.5.0 · sourceimpl FromStr for SocketAddrV4
impl FromStr for SocketAddrV4
type Err = AddrParseError
pub fn from_str(s: &str) -> Result<SocketAddrV4, AddrParseError>
sourceimpl FromStr for Ipv4Addr
impl FromStr for Ipv4Addr
type Err = AddrParseError
pub fn from_str(s: &str) -> Result<Ipv4Addr, AddrParseError>
sourceimpl FromStr for SocketAddr
impl FromStr for SocketAddr
type Err = AddrParseError
pub fn from_str(s: &str) -> Result<SocketAddr, AddrParseError>
1.7.0 · sourceimpl FromStr for IpAddr
impl FromStr for IpAddr
type Err = AddrParseError
pub fn from_str(s: &str) -> Result<IpAddr, AddrParseError>
sourceimpl FromStr for Ipv6Addr
impl FromStr for Ipv6Addr
type Err = AddrParseError
pub fn from_str(s: &str) -> Result<Ipv6Addr, AddrParseError>
sourceimpl FromStr for i32
impl FromStr for i32
type Err = ParseIntError
pub fn from_str(src: &str) -> Result<i32, ParseIntError>
sourceimpl FromStr for u32
impl FromStr for u32
type Err = ParseIntError
pub fn from_str(src: &str) -> Result<u32, ParseIntError>
sourceimpl FromStr for u128
impl FromStr for u128
type Err = ParseIntError
pub fn from_str(src: &str) -> Result<u128, ParseIntError>
sourceimpl FromStr for i128
impl FromStr for i128
type Err = ParseIntError
pub fn from_str(src: &str) -> Result<i128, ParseIntError>
sourceimpl FromStr for i16
impl FromStr for i16
type Err = ParseIntError
pub fn from_str(src: &str) -> Result<i16, ParseIntError>
sourceimpl FromStr for u64
impl FromStr for u64
type Err = ParseIntError
pub fn from_str(src: &str) -> Result<u64, ParseIntError>
sourceimpl FromStr for u16
impl FromStr for u16
type Err = ParseIntError
pub fn from_str(src: &str) -> Result<u16, ParseIntError>
sourceimpl FromStr for usize
impl FromStr for usize
type Err = ParseIntError
pub fn from_str(src: &str) -> Result<usize, ParseIntError>
sourceimpl FromStr for i8
impl FromStr for i8
type Err = ParseIntError
pub fn from_str(src: &str) -> Result<i8, ParseIntError>
sourceimpl FromStr for u8
impl FromStr for u8
type Err = ParseIntError
pub fn from_str(src: &str) -> Result<u8, ParseIntError>
sourceimpl FromStr for bool
impl FromStr for bool
sourcepub fn from_str(s: &str) -> Result<bool, ParseBoolError>
pub fn from_str(s: &str) -> Result<bool, ParseBoolError>
Parse a bool from a string.
Yields a Result<bool, ParseBoolError>, because s may or may not
actually be parseable.
Examples
use std::str::FromStr;
assert_eq!(FromStr::from_str("true"), Ok(true));
assert_eq!(FromStr::from_str("false"), Ok(false));
assert!(<bool as FromStr>::from_str("not even a boolean").is_err());Note, in many cases, the .parse() method on str is more proper.
assert_eq!("true".parse(), Ok(true));
assert_eq!("false".parse(), Ok(false));
assert!("not even a boolean".parse::<bool>().is_err());type Err = ParseBoolError
sourceimpl FromStr for i64
impl FromStr for i64
type Err = ParseIntError
pub fn from_str(src: &str) -> Result<i64, ParseIntError>
sourceimpl FromStr for isize
impl FromStr for isize
type Err = ParseIntError
pub fn from_str(src: &str) -> Result<isize, ParseIntError>
sourceimpl FromStr for f32
impl FromStr for f32
sourcepub fn from_str(src: &str) -> Result<f32, ParseFloatError>
pub fn from_str(src: &str) -> Result<f32, ParseFloatError>
Converts a string in base 10 to a float. Accepts an optional decimal exponent.
This function accepts strings such as
- ‘3.14’
- ‘-3.14’
- ‘2.5E10’, or equivalently, ‘2.5e10’
- ‘2.5E-10’
- ‘5.’
- ‘.5’, or, equivalently, ‘0.5’
- ‘inf’, ‘-inf’, ‘NaN’
Leading and trailing whitespace represent an error.
Grammar
All strings that adhere to the following EBNF grammar
will result in an Ok being returned:
Float ::= Sign? ( 'inf' | 'NaN' | Number )
Number ::= ( Digit+ |
Digit+ '.' Digit* |
Digit* '.' Digit+ ) Exp?
Exp ::= [eE] Sign? Digit+
Sign ::= [+-]
Digit ::= [0-9]Arguments
- src - A string
Return value
Err(ParseFloatError) if the string did not represent a valid
number. Otherwise, Ok(n) where n is the floating-point
number represented by src.
type Err = ParseFloatError
sourceimpl FromStr for f64
impl FromStr for f64
sourcepub fn from_str(src: &str) -> Result<f64, ParseFloatError>
pub fn from_str(src: &str) -> Result<f64, ParseFloatError>
Converts a string in base 10 to a float. Accepts an optional decimal exponent.
This function accepts strings such as
- ‘3.14’
- ‘-3.14’
- ‘2.5E10’, or equivalently, ‘2.5e10’
- ‘2.5E-10’
- ‘5.’
- ‘.5’, or, equivalently, ‘0.5’
- ‘inf’, ‘-inf’, ‘NaN’
Leading and trailing whitespace represent an error.
Grammar
All strings that adhere to the following EBNF grammar
will result in an Ok being returned:
Float ::= Sign? ( 'inf' | 'NaN' | Number )
Number ::= ( Digit+ |
Digit+ '.' Digit* |
Digit* '.' Digit+ ) Exp?
Exp ::= [eE] Sign? Digit+
Sign ::= [+-]
Digit ::= [0-9]Arguments
- src - A string
Return value
Err(ParseFloatError) if the string did not represent a valid
number. Otherwise, Ok(n) where n is the floating-point
number represented by src.