Trait nom::lib::std::str::FromStr1.0.0[−][src]

pub trait FromStr {
    type Err;
    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;
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

The associated error which can be returned from parsing.

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

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.

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());

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.

Implementors

impl<A> FromStr for ArrayString<A> where
    A: Array<Item = u8> + Copy, 

impl FromStr for Cfg

impl FromStr for CfgExpr

impl FromStr for Platform

impl FromStr for Endian

impl FromStr for DateTime<Utc>

impl FromStr for Weekday

impl FromStr for Month

impl<T: FromStr> FromStr for DebugIgnore<T>

impl FromStr for Duration

impl FromStr for Level

impl FromStr for Signal

impl FromStr for Literal

impl FromStr for Regex

impl FromStr for Regex

impl FromStr for Version

impl FromStr for Number

impl FromStr for Value

impl FromStr for Vendor

impl FromStr for Triple

impl FromStr for Triple

impl FromStr for Color

impl FromStr for Value

impl FromStr for Datetime