# Trait alloc::str::FromStr

1.0.0 · source ·

    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());

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## 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);

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## Implementors§

1.7.0 · source§

### impl FromStr for IpAddr

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#### type Err = AddrParseError

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### impl FromStr for SocketAddr

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#### type Err = AddrParseError

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### impl FromStr for bool

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#### type Err = ParseBoolError

1.20.0 · source§

### impl FromStr for char

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#### type Err = ParseCharError

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### impl FromStr for f32

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#### type Err = ParseFloatError

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### impl FromStr for f64

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#### type Err = ParseFloatError

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### impl FromStr for i8

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#### type Err = ParseIntError

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### impl FromStr for i16

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#### type Err = ParseIntError

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### impl FromStr for i32

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#### type Err = ParseIntError

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### impl FromStr for i64

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#### type Err = ParseIntError

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### impl FromStr for i128

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#### type Err = ParseIntError

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### impl FromStr for isize

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#### type Err = ParseIntError

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### impl FromStr for u8

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#### type Err = ParseIntError

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### impl FromStr for u16

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#### type Err = ParseIntError

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### impl FromStr for u32

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#### type Err = ParseIntError

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### impl FromStr for u64

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#### type Err = ParseIntError

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### impl FromStr for u128

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#### type Err = ParseIntError

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### impl FromStr for usize

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#### type Err = ParseIntError

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### impl FromStr for Ipv4Addr

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#### type Err = AddrParseError

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### impl FromStr for Ipv6Addr

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#### type Err = AddrParseError

1.5.0 · source§

### impl FromStr for SocketAddrV4

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#### type Err = AddrParseError

1.5.0 · source§

### impl FromStr for SocketAddrV6

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#### type Err = AddrParseError

1.35.0 · source§

### impl FromStr for NonZeroI8

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#### type Err = ParseIntError

1.35.0 · source§

### impl FromStr for NonZeroI16

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#### type Err = ParseIntError

1.35.0 · source§

### impl FromStr for NonZeroI32

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#### type Err = ParseIntError

1.35.0 · source§

### impl FromStr for NonZeroI64

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#### type Err = ParseIntError

1.35.0 · source§

### impl FromStr for NonZeroI128

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#### type Err = ParseIntError

1.35.0 · source§

### impl FromStr for NonZeroIsize

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#### type Err = ParseIntError

1.35.0 · source§

### impl FromStr for NonZeroU8

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#### type Err = ParseIntError

1.35.0 · source§

### impl FromStr for NonZeroU16

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#### type Err = ParseIntError

1.35.0 · source§

### impl FromStr for NonZeroU32

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#### type Err = ParseIntError

1.35.0 · source§

### impl FromStr for NonZeroU64

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#### type Err = ParseIntError

1.35.0 · source§

### impl FromStr for NonZeroU128

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#### type Err = ParseIntError

1.35.0 · source§

### impl FromStr for NonZeroUsize

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#### type Err = ParseIntError

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### impl FromStr for String

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#### type Err = Infallible