Trait core::convert::From

pub trait From<T>: Sized {
    // Required method
    fn from(value: T) -> Self;
}

Used to do value-to-value conversions while consuming the input value. It is the reciprocal of Into.

One should always prefer implementing From over Into because implementing From automatically provides one with an implementation of Into thanks to the blanket implementation in the standard library.

Only implement Into when targeting a version prior to Rust 1.41 and converting to a type outside the current crate. From was not able to do these types of conversions in earlier versions because of Rust’s orphaning rules. See Into for more details.

Prefer using Into over using From when specifying trait bounds on a generic function. This way, types that directly implement Into can be used as arguments as well.

The From is also very useful when performing error handling. When constructing a function that is capable of failing, the return type will generally be of the form Result<T, E>. The From trait simplifies error handling by allowing a function to return a single error type that encapsulate multiple error types. See the “Examples” section and the book for more details.

Note: This trait must not fail. The From trait is intended for perfect conversions. If the conversion can fail or is not perfect, use TryFrom.

Generic Implementations

• From<T> for U implies Into<U> for T
• From is reflexive, which means that From<T> for T is implemented

Examples

String implements From<&str>:

An explicit conversion from a &str to a String is done as follows:

let string = "hello".to_string();
let other_string = String::from("hello");

assert_eq!(string, other_string);

While performing error handling it is often useful to implement From for your own error type. By converting underlying error types to our own custom error type that encapsulates the underlying error type, we can return a single error type without losing information on the underlying cause. The ‘?’ operator automatically converts the underlying error type to our custom error type by calling Into<CliError>::into which is automatically provided when implementing From. The compiler then infers which implementation of Into should be used.

use std::fs;
use std::io;
use std::num;

enum CliError {
    IoError(io::Error),
    ParseError(num::ParseIntError),
}

impl From<io::Error> for CliError {
    fn from(error: io::Error) -> Self {
        CliError::IoError(error)
    }
}

impl From<num::ParseIntError> for CliError {
    fn from(error: num::ParseIntError) -> Self {
        CliError::ParseError(error)
    }
}

fn open_and_parse_file(file_name: &str) -> Result<i32, CliError> {
    let mut contents = fs::read_to_string(&file_name)?;
    let num: i32 = contents.trim().parse()?;
    Ok(num)
}

Required Methods

fn from(value: T) -> Self

Converts to this type from the input type.

Implementors

impl From<Infallible> for TryFromSliceError

impl From<Infallible> for TryFromIntError

impl From<bool> for f32

impl From<bool> for f64

impl From<bool> for i8

impl From<bool> for i16

impl From<bool> for i32

impl From<bool> for i64

impl From<bool> for i128

impl From<bool> for isize

impl From<bool> for u8

impl From<bool> for u16

impl From<bool> for u32

impl From<bool> for u64

impl From<bool> for u128

impl From<bool> for usize

impl From<bool> for AtomicBool

impl From<char> for u32

impl From<char> for u64

impl From<char> for u128

impl From<f32> for f64

impl From<i8> for f32

impl From<i8> for f64

impl From<i8> for i16

impl From<i8> for i32

impl From<i8> for i64

impl From<i8> for i128

impl From<i8> for isize

impl From<i8> for AtomicI8

impl From<i16> for f32

impl From<i16> for f64

impl From<i16> for i32

impl From<i16> for i64

impl From<i16> for i128

impl From<i16> for isize

impl From<i16> for AtomicI16

impl From<i32> for f64

impl From<i32> for i64

impl From<i32> for i128

impl From<i32> for AtomicI32

impl From<i64> for i128

impl From<i64> for AtomicI64

impl From<isize> for AtomicIsize

impl From<!> for Infallible

impl From<!> for TryFromIntError

impl From<u8> for char

Maps a byte in 0x00..=0xFF to a char whose code point has the same value, in U+0000..=U+00FF.

Unicode is designed such that this effectively decodes bytes with the character encoding that IANA calls ISO-8859-1. This encoding is compatible with ASCII.

Note that this is different from ISO/IEC 8859-1 a.k.a. ISO 8859-1 (with one less hyphen), which leaves some “blanks”, byte values that are not assigned to any character. ISO-8859-1 (the IANA one) assigns them to the C0 and C1 control codes.

Note that this is also different from Windows-1252 a.k.a. code page 1252, which is a superset ISO/IEC 8859-1 that assigns some (not all!) blanks to punctuation and various Latin characters.

To confuse things further, on the Web ascii, iso-8859-1, and windows-1252 are all aliases for a superset of Windows-1252 that fills the remaining blanks with corresponding C0 and C1 control codes.

impl From<u8> for f32

impl From<u8> for f64

impl From<u8> for i16

impl From<u8> for i32

impl From<u8> for i64

impl From<u8> for i128

impl From<u8> for isize

impl From<u8> for u16

impl From<u8> for u32

impl From<u8> for u64

impl From<u8> for u128

impl From<u8> for usize

impl From<u8> for AtomicU8

impl From<u16> for f32

impl From<u16> for f64

impl From<u16> for i32

impl From<u16> for i64

impl From<u16> for i128

impl From<u16> for u32

impl From<u16> for u64

impl From<u16> for u128

impl From<u16> for usize

impl From<u16> for AtomicU16

impl From<u32> for f64

impl From<u32> for i64

impl From<u32> for i128

impl From<u32> for u64

impl From<u32> for u128

impl From<u32> for Ipv4Addr

impl From<u32> for AtomicU32

impl From<u64> for i128

impl From<u64> for u128

impl From<u64> for AtomicU64

impl From<u128> for Ipv6Addr

impl From<usize> for AtomicUsize

impl From<__m128> for f32x4

impl From<__m128d> for f64x2

impl From<__m128i> for i8x16

impl From<__m128i> for i16x8

impl From<__m128i> for i32x4

impl From<__m128i> for i64x2

impl From<__m128i> for isizex2

impl From<__m128i> for u8x16

impl From<__m128i> for u16x8

impl From<__m128i> for u32x4

impl From<__m128i> for u64x2

impl From<__m128i> for usizex2

impl From<__m256> for f32x8

impl From<__m256d> for f64x4

impl From<__m256i> for i8x32

impl From<__m256i> for i16x16

impl From<__m256i> for i32x8

impl From<__m256i> for i64x4

impl From<__m256i> for isizex4

impl From<__m256i> for u8x32

impl From<__m256i> for u16x16

impl From<__m256i> for u32x8

impl From<__m256i> for u64x4

impl From<__m256i> for usizex4

impl From<__m512> for f32x16

impl From<__m512d> for f64x8

impl From<__m512i> for i8x64

impl From<__m512i> for i16x32

impl From<__m512i> for i32x16

impl From<__m512i> for i64x8

impl From<__m512i> for isizex8

impl From<__m512i> for u8x64

impl From<__m512i> for u16x32

impl From<__m512i> for u32x16

impl From<__m512i> for u64x8

impl From<__m512i> for usizex8

impl From<Ipv4Addr> for IpAddr

impl From<Ipv4Addr> for u32

impl From<Ipv6Addr> for IpAddr

impl From<Ipv6Addr> for u128

impl From<SocketAddrV4> for SocketAddr

impl From<SocketAddrV6> for SocketAddr

impl From<NonZeroI8> for i8

impl From<NonZeroI8> for NonZeroI16

impl From<NonZeroI8> for NonZeroI32

impl From<NonZeroI8> for NonZeroI64

impl From<NonZeroI8> for NonZeroI128

impl From<NonZeroI8> for NonZeroIsize

impl From<NonZeroI16> for i16

impl From<NonZeroI16> for NonZeroI32

impl From<NonZeroI16> for NonZeroI64

impl From<NonZeroI16> for NonZeroI128

impl From<NonZeroI16> for NonZeroIsize

impl From<NonZeroI32> for i32

impl From<NonZeroI32> for NonZeroI64

impl From<NonZeroI32> for NonZeroI128

impl From<NonZeroI64> for i64

impl From<NonZeroI64> for NonZeroI128

impl From<NonZeroI128> for i128

impl From<NonZeroIsize> for isize

impl From<NonZeroU8> for u8

impl From<NonZeroU8> for NonZeroI16

impl From<NonZeroU8> for NonZeroI32

impl From<NonZeroU8> for NonZeroI64

impl From<NonZeroU8> for NonZeroI128

impl From<NonZeroU8> for NonZeroIsize

impl From<NonZeroU8> for NonZeroU16

impl From<NonZeroU8> for NonZeroU32

impl From<NonZeroU8> for NonZeroU64

impl From<NonZeroU8> for NonZeroU128

impl From<NonZeroU8> for NonZeroUsize

impl From<NonZeroU16> for u16

impl From<NonZeroU16> for NonZeroI32

impl From<NonZeroU16> for NonZeroI64

impl From<NonZeroU16> for NonZeroI128

impl From<NonZeroU16> for NonZeroU32

impl From<NonZeroU16> for NonZeroU64

impl From<NonZeroU16> for NonZeroU128

impl From<NonZeroU16> for NonZeroUsize

impl From<NonZeroU32> for u32

impl From<NonZeroU32> for NonZeroI64

impl From<NonZeroU32> for NonZeroI128

impl From<NonZeroU32> for NonZeroU64

impl From<NonZeroU32> for NonZeroU128

impl From<NonZeroU64> for u64

impl From<NonZeroU64> for NonZeroI128

impl From<NonZeroU64> for NonZeroU128

impl From<NonZeroU128> for u128

impl From<NonZeroUsize> for usize

impl From<Alignment> for usize

impl From<Alignment> for NonZeroUsize

impl From<Simd<f32, 4>> for __m128

impl From<Simd<f32, 8>> for __m256

impl From<Simd<f32, 16>> for __m512

impl From<Simd<f64, 2>> for __m128d

impl From<Simd<f64, 4>> for __m256d

impl From<Simd<f64, 8>> for __m512d

impl From<Simd<i8, 16>> for __m128i

impl From<Simd<i8, 32>> for __m256i

impl From<Simd<i8, 64>> for __m512i

impl From<Simd<i16, 8>> for __m128i

impl From<Simd<i16, 16>> for __m256i

impl From<Simd<i16, 32>> for __m512i

impl From<Simd<i32, 4>> for __m128i

impl From<Simd<i32, 8>> for __m256i

impl From<Simd<i32, 16>> for __m512i

impl From<Simd<i64, 2>> for __m128i

impl From<Simd<i64, 4>> for __m256i

impl From<Simd<i64, 8>> for __m512i

impl From<Simd<isize, 2>> for __m128i

impl From<Simd<isize, 4>> for __m256i

impl From<Simd<isize, 8>> for __m512i

impl From<Simd<u8, 16>> for __m128i

impl From<Simd<u8, 32>> for __m256i

impl From<Simd<u8, 64>> for __m512i

impl From<Simd<u16, 8>> for __m128i

impl From<Simd<u16, 16>> for __m256i

impl From<Simd<u16, 32>> for __m512i

impl From<Simd<u32, 4>> for __m128i

impl From<Simd<u32, 8>> for __m256i

impl From<Simd<u32, 16>> for __m512i

impl From<Simd<u64, 2>> for __m128i

impl From<Simd<u64, 4>> for __m256i

impl From<Simd<u64, 8>> for __m512i

impl From<Simd<usize, 2>> for __m128i

impl From<Simd<usize, 4>> for __m256i

impl From<Simd<usize, 8>> for __m512i

impl From<[u8; 4]> for IpAddr

impl From<[u8; 4]> for Ipv4Addr

impl From<[u8; 16]> for IpAddr

impl From<[u8; 16]> for Ipv6Addr

impl From<[u16; 8]> for IpAddr

impl From<[u16; 8]> for Ipv6Addr

impl<'a, T> From<&'a Option<T>> for Option<&'a T>

impl<'a, T> From<&'a mut Option<T>> for Option<&'a mut T>

impl<I: Into<IpAddr>> From<(I, u16)> for SocketAddr

impl<T> From<!> for T

Stability note: This impl does not yet exist, but we are “reserving space” to add it in the future. See rust-lang/rust#64715 for details.

impl<T> From<*mut T> for AtomicPtr<T>

impl<T> From<T> for Option<T>

impl<T> From<T> for Poll<T>

impl<T> From<T> for Cell<T>

impl<T> From<T> for OnceCell<T>

impl<T> From<T> for RefCell<T>

impl<T> From<T> for SyncUnsafeCell<T>

impl<T> From<T> for UnsafeCell<T>

impl<T> From<T> for Exclusive<T>

impl<T> From<T> for T

impl<T, const LANES: usize> From<[T; LANES]> for Simd<T, LANES>where LaneCount<LANES>: SupportedLaneCount, T: SimdElement,

impl<T, const LANES: usize> From<Mask<T, LANES>> for [bool; LANES]where T: MaskElement, LaneCount<LANES>: SupportedLaneCount,

impl<T, const LANES: usize> From<Simd<T, LANES>> for [T; LANES]where LaneCount<LANES>: SupportedLaneCount, T: SimdElement,

impl<T, const LANES: usize> From<[bool; LANES]> for Mask<T, LANES>where T: MaskElement, LaneCount<LANES>: SupportedLaneCount,

impl<T: ?Sized> From<&T> for NonNull<T>

impl<T: ?Sized> From<&mut T> for NonNull<T>

impl<const LANES: usize> From<Mask<i8, LANES>> for Mask<i16, LANES>where LaneCount<LANES>: SupportedLaneCount,

impl<const LANES: usize> From<Mask<i8, LANES>> for Mask<i32, LANES>where LaneCount<LANES>: SupportedLaneCount,

impl<const LANES: usize> From<Mask<i8, LANES>> for Mask<i64, LANES>where LaneCount<LANES>: SupportedLaneCount,

impl<const LANES: usize> From<Mask<i8, LANES>> for Mask<isize, LANES>where LaneCount<LANES>: SupportedLaneCount,

impl<const LANES: usize> From<Mask<i16, LANES>> for Mask<i8, LANES>where LaneCount<LANES>: SupportedLaneCount,

impl<const LANES: usize> From<Mask<i16, LANES>> for Mask<i32, LANES>where LaneCount<LANES>: SupportedLaneCount,

impl<const LANES: usize> From<Mask<i16, LANES>> for Mask<i64, LANES>where LaneCount<LANES>: SupportedLaneCount,

impl<const LANES: usize> From<Mask<i16, LANES>> for Mask<isize, LANES>where LaneCount<LANES>: SupportedLaneCount,

impl<const LANES: usize> From<Mask<i32, LANES>> for Mask<i8, LANES>where LaneCount<LANES>: SupportedLaneCount,

impl<const LANES: usize> From<Mask<i32, LANES>> for Mask<i16, LANES>where LaneCount<LANES>: SupportedLaneCount,

impl<const LANES: usize> From<Mask<i32, LANES>> for Mask<i64, LANES>where LaneCount<LANES>: SupportedLaneCount,

impl<const LANES: usize> From<Mask<i32, LANES>> for Mask<isize, LANES>where LaneCount<LANES>: SupportedLaneCount,

impl<const LANES: usize> From<Mask<i64, LANES>> for Mask<i8, LANES>where LaneCount<LANES>: SupportedLaneCount,

impl<const LANES: usize> From<Mask<i64, LANES>> for Mask<i16, LANES>where LaneCount<LANES>: SupportedLaneCount,

impl<const LANES: usize> From<Mask<i64, LANES>> for Mask<i32, LANES>where LaneCount<LANES>: SupportedLaneCount,

impl<const LANES: usize> From<Mask<i64, LANES>> for Mask<isize, LANES>where LaneCount<LANES>: SupportedLaneCount,

impl<const LANES: usize> From<Mask<isize, LANES>> for Mask<i8, LANES>where LaneCount<LANES>: SupportedLaneCount,

impl<const LANES: usize> From<Mask<isize, LANES>> for Mask<i16, LANES>where LaneCount<LANES>: SupportedLaneCount,

impl<const LANES: usize> From<Mask<isize, LANES>> for Mask<i32, LANES>where LaneCount<LANES>: SupportedLaneCount,

impl<const LANES: usize> From<Mask<isize, LANES>> for Mask<i64, LANES>where LaneCount<LANES>: SupportedLaneCount,