Trait alloc_data::prelude::FromStr

1.0.0 · source · [−]
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 (x, y) = s
            .strip_prefix('(')
            .and_then(|s| s.strip_suffix(')'))
            .and_then(|s| s.split_once(','))
            .unwrap();

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

        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);

Required 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);

Implementors

Parsing a str into a Month uses the format %W.

Example

use chrono::Month;

assert_eq!("January".parse::<Month>(), Ok(Month::January));
assert!("any day".parse::<Month>().is_err());

The parsing is case-insensitive.

assert_eq!("fEbruARy".parse::<Month>(), Ok(Month::February));

Only the shortest form (e.g. jan) and the longest form (e.g. january) is accepted.

assert!("septem".parse::<Month>().is_err());
assert!("Augustin".parse::<Month>().is_err());

Parsing a str into a Weekday uses the format %W.

Example

use chrono::Weekday;

assert_eq!("Sunday".parse::<Weekday>(), Ok(Weekday::Sun));
assert!("any day".parse::<Weekday>().is_err());

The parsing is case-insensitive.

assert_eq!("mON".parse::<Weekday>(), Ok(Weekday::Mon));

Only the shortest form (e.g. sun) and the longest form (e.g. sunday) is accepted.

assert!("thurs".parse::<Weekday>().is_err());

Accepts a relaxed form of RFC3339. A space or a ‘T’ are acepted as the separator between the date and time parts. Additional spaces are allowed between each component.

All of these examples are equivalent:

"2012-12-12T12:12:12Z".parse::<DateTime<FixedOffset>>();
"2012-12-12 12:12:12Z".parse::<DateTime<FixedOffset>>();
"2012-  12-12T12:  12:12Z".parse::<DateTime<FixedOffset>>();

Accepts a relaxed form of RFC3339. A space or a ‘T’ are acepted as the separator between the date and time parts. Additional spaces are allowed between each component.

All of these examples are equivalent:

"2012-12-12T12:12:12Z".parse::<DateTime<Local>>();
"2012-12-12 12:12:12Z".parse::<DateTime<Local>>();
"2012-  12-12T12:  12:12Z".parse::<DateTime<Local>>();

Accepts a relaxed form of RFC3339. A space or a ‘T’ are acepted as the separator between the date and time parts. Additional spaces are allowed between each component.

All of these examples are equivalent:

"2012-12-12T12:12:12Z".parse::<DateTime<Utc>>();
"2012-12-12 12:12:12Z".parse::<DateTime<Utc>>();
"2012-  12-12T12:  12:12Z".parse::<DateTime<Utc>>();

Parsing a str into a NaiveDate uses the same format, %Y-%m-%d, as in Debug and Display.

Example

use chrono::NaiveDate;

let d = NaiveDate::from_ymd(2015, 9, 18);
assert_eq!("2015-09-18".parse::<NaiveDate>(), Ok(d));

let d = NaiveDate::from_ymd(12345, 6, 7);
assert_eq!("+12345-6-7".parse::<NaiveDate>(), Ok(d));

assert!("foo".parse::<NaiveDate>().is_err());

Parsing a str into a NaiveDateTime uses the same format, %Y-%m-%dT%H:%M:%S%.f, as in Debug.

Example

use chrono::{NaiveDateTime, NaiveDate};

let dt = NaiveDate::from_ymd(2015, 9, 18).and_hms(23, 56, 4);
assert_eq!("2015-09-18T23:56:04".parse::<NaiveDateTime>(), Ok(dt));

let dt = NaiveDate::from_ymd(12345, 6, 7).and_hms_milli(7, 59, 59, 1_500); // leap second
assert_eq!("+12345-6-7T7:59:60.5".parse::<NaiveDateTime>(), Ok(dt));

assert!("foo".parse::<NaiveDateTime>().is_err());

Parsing a str into a NaiveTime uses the same format, %H:%M:%S%.f, as in Debug and Display.

Example

use chrono::NaiveTime;

let t = NaiveTime::from_hms(23, 56, 4);
assert_eq!("23:56:04".parse::<NaiveTime>(), Ok(t));

let t = NaiveTime::from_hms_nano(23, 56, 4, 12_345_678);
assert_eq!("23:56:4.012345678".parse::<NaiveTime>(), Ok(t));

let t = NaiveTime::from_hms_nano(23, 59, 59, 1_234_567_890); // leap second
assert_eq!("23:59:60.23456789".parse::<NaiveTime>(), Ok(t));

assert!("foo".parse::<NaiveTime>().is_err());