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.

§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§

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type Err

The associated error which can be returned from parsing.

Required Methods§

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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);

Object Safety§

This trait is not object safe.

Implementors§

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impl FromStr for Level

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type Err = String

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impl FromStr for NonFungibleLocalId

1.7.0 · source§

impl FromStr for IpAddr

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impl FromStr for SocketAddr

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impl FromStr for bool

1.20.0 · source§

impl FromStr for char

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impl FromStr for f32

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impl FromStr for f64

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impl FromStr for i8

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impl FromStr for i16

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impl FromStr for i32

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impl FromStr for i64

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impl FromStr for i128

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impl FromStr for isize

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impl FromStr for u8

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impl FromStr for u16

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impl FromStr for u32

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impl FromStr for u64

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impl FromStr for u128

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impl FromStr for usize

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impl FromStr for Bls12381G1PublicKey

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impl FromStr for Bls12381G2Signature

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impl FromStr for Decimal

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impl FromStr for Ed25519PublicKey

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impl FromStr for Ed25519Signature

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impl FromStr for Hash

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impl FromStr for I192

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impl FromStr for I256

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impl FromStr for I320

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impl FromStr for I384

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impl FromStr for I448

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impl FromStr for I512

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impl FromStr for I768

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impl FromStr for NetworkDefinition

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impl FromStr for PreciseDecimal

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impl FromStr for Secp256k1PublicKey

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impl FromStr for Secp256k1Signature

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impl FromStr for String

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impl FromStr for U192

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impl FromStr for U256

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impl FromStr for U320

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impl FromStr for U384

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impl FromStr for U448

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impl FromStr for U512

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impl FromStr for U768

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impl FromStr for UtcDateTime

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impl FromStr for Ipv4Addr

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impl FromStr for Ipv6Addr

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impl FromStr for SocketAddrV4

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impl FromStr for SocketAddrV6

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impl FromStr for proc_macro::Literal

Parse a single literal from its stringified representation.

In order to parse successfully, the input string must not contain anything but the literal token. Specifically, it must not contain whitespace or comments in addition to the literal.

The resulting literal token will have a Span::call_site() span.

NOTE: some errors may cause panics instead of returning LexError. We reserve the right to change these errors into LexErrors later.

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impl FromStr for proc_macro::TokenStream

Attempts to break the string into tokens and parse those tokens into a token stream. May fail for a number of reasons, for example, if the string contains unbalanced delimiters or characters not existing in the language. All tokens in the parsed stream get Span::call_site() spans.

NOTE: some errors may cause panics instead of returning LexError. We reserve the right to change these errors into LexErrors later.

1.45.0 · source§

impl FromStr for OsString

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impl FromStr for PathBuf

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impl FromStr for BigInt

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impl FromStr for BigUint

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impl FromStr for proc_macro2::Literal

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impl FromStr for proc_macro2::TokenStream

Attempts to break the string into tokens and parse those tokens into a token stream.

May fail for a number of reasons, for example, if the string contains unbalanced delimiters or characters not existing in the language.

NOTE: Some errors may cause panics instead of returning LexError. We reserve the right to change these errors into LexErrors later.

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impl FromStr for BuildMetadata

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type Err = Error

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impl FromStr for Comparator

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type Err = Error

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impl FromStr for Prerelease

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type Err = Error

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impl FromStr for Version

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type Err = Error

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impl FromStr for VersionReq

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type Err = Error

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impl FromStr for Uuid

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type Err = Error

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impl FromStr for NonZero<i8>

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impl FromStr for NonZero<i16>

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impl FromStr for NonZero<i32>

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impl FromStr for NonZero<i64>

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impl FromStr for NonZero<i128>

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impl FromStr for NonZero<isize>

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impl FromStr for NonZero<u8>

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impl FromStr for NonZero<u16>

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impl FromStr for NonZero<u32>

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impl FromStr for NonZero<u64>

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impl FromStr for NonZero<u128>

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impl FromStr for NonZero<usize>

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impl FromStr for Color

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type Err = ()

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impl FromStr for KeyPair

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type Err = Error

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impl FromStr for PublicKey

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type Err = Error

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impl FromStr for Regex

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type Err = Error

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impl FromStr for Regex

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type Err = Error

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impl FromStr for SecretKey

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type Err = Error

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impl FromStr for SharedSecret

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type Err = Error

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impl FromStr for Signature

Decode a signature from hexadecimal.

Upper and lower case hexadecimal are both accepted, however mixed case is rejected.

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type Err = Error

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impl FromStr for Signature

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type Err = Error

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impl FromStr for Signature

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type Err = Error

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impl FromStr for XOnlyPublicKey

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type Err = Error

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impl<const N: usize> FromStr for BInt<N>

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type Err = ParseIntError

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impl<const N: usize> FromStr for BIntD8<N>

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type Err = ParseIntError

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impl<const N: usize> FromStr for BIntD16<N>

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type Err = ParseIntError

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impl<const N: usize> FromStr for BIntD32<N>

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type Err = ParseIntError

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impl<const N: usize> FromStr for BUint<N>

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type Err = ParseIntError

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impl<const N: usize> FromStr for BUintD8<N>

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type Err = ParseIntError

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impl<const N: usize> FromStr for BUintD16<N>

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type Err = ParseIntError

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impl<const N: usize> FromStr for BUintD32<N>

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type Err = ParseIntError