Trait sp_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 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]

Known bugs

In some situations, some strings that should create a valid float instead return an error. See issue #31407 for details.

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]

Known bugs

In some situations, some strings that should create a valid float instead return an error. See issue #31407 for details.

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 FromStr for Mode

impl<Hash: FromStr, Number: FromStr> FromStr for BlockAddress<Hash, Number>

impl<Hash: FromStr + Debug, Number: FromStr + Debug> FromStr for ExtrinsicAddress<Hash, Number>

impl FromStr for WasmExecutionMethod

impl FromStr for TracingReceiver

impl FromStr for NodeKeyType

impl FromStr for CryptoScheme

impl FromStr for OutputType

impl FromStr for ExecutionStrategy

impl FromStr for RpcMethods

impl FromStr for Database

impl FromStr for OffchainWorkerEnabled

impl FromStr for SyncMode

impl FromStr for GenericNumber

impl FromStr for BlockNumberOrHash

impl FromStr for MultiaddrWithPeerId

impl FromStr for FixedI64

impl FromStr for FixedI128

impl FromStr for FixedU128

impl FromStr for Ss58AddressFormat

impl FromStr for AccountId32

impl FromStr for Public

impl FromStr for Public

impl FromStr for Bytes

impl FromStr for Keyring