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1.0.0[][src]Trait core::convert::From

pub trait From<T>: Sized {
    fn from(_: T) -> Self;

Simple and safe type conversions in to Self. It is the reciprocal of Into.

This trait is useful when performing error handling as described by the book and is closely related to the ? operator.

When constructing a function that is capable of failing the return type will generally be of the form Result<T, E>.

The From trait allows for simplification of error handling by providing a means of returning a single error type that encapsulates numerous possible erroneous situations.

This trait is not limited to error handling, rather the general case for this trait would be in any type conversions to have an explicit definition of how they are performed.

Note: this trait must not fail. If the conversion can fail, use TryFrom or a dedicated method which returns an Option<T> or a Result<T, E>.

Generic Implementations


String implements From<&str>:

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

assert_eq!(string, other_string);Run

An example usage for error handling:

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

enum CliError {

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

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

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()?;

Required methods

fn from(_: T) -> Self

Performs the conversion.

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impl From<!> for Infallible[src]

impl From<!> for TryFromIntError[src]

impl From<Infallible> for TryFromIntError[src]

impl From<NonZeroI128> for i128[src]

impl From<NonZeroI16> for i16[src]

impl From<NonZeroI32> for i32[src]

impl From<NonZeroI64> for i64[src]

impl From<NonZeroI8> for i8[src]

impl From<NonZeroIsize> for isize[src]

impl From<NonZeroU128> for u128[src]

impl From<NonZeroU16> for u16[src]

impl From<NonZeroU32> for u32[src]

impl From<NonZeroU64> for u64[src]

impl From<NonZeroU8> for u8[src]

impl From<NonZeroUsize> for usize[src]

impl From<bool> for AtomicBool[src]

fn from(b: bool) -> Self[src]

Converts a bool into an AtomicBool.


use std::sync::atomic::AtomicBool;
let atomic_bool = AtomicBool::from(true);
assert_eq!(format!("{:?}", atomic_bool), "true")Run

impl From<bool> for i8[src]

Converts a bool to a i8. The resulting value is 0 for false and 1 for true values.


assert_eq!(i8::from(true), 1);
assert_eq!(i8::from(false), 0);Run

impl From<bool> for i16[src]

Converts a bool to a i16. The resulting value is 0 for false and 1 for true values.


assert_eq!(i16::from(true), 1);
assert_eq!(i16::from(false), 0);Run

impl From<bool> for i32[src]

Converts a bool to a i32. The resulting value is 0 for false and 1 for true values.


assert_eq!(i32::from(true), 1);
assert_eq!(i32::from(false), 0);Run

impl From<bool> for i64[src]

Converts a bool to a i64. The resulting value is 0 for false and 1 for true values.


assert_eq!(i64::from(true), 1);
assert_eq!(i64::from(false), 0);Run

impl From<bool> for i128[src]

Converts a bool to a i128. The resulting value is 0 for false and 1 for true values.


assert_eq!(i128::from(true), 1);
assert_eq!(i128::from(false), 0);Run

impl From<bool> for isize[src]

Converts a bool to a isize. The resulting value is 0 for false and 1 for true values.


assert_eq!(isize::from(true), 1);
assert_eq!(isize::from(false), 0);Run

impl From<bool> for u8[src]

Converts a bool to a u8. The resulting value is 0 for false and 1 for true values.


assert_eq!(u8::from(true), 1);
assert_eq!(u8::from(false), 0);Run

impl From<bool> for u16[src]

Converts a bool to a u16. The resulting value is 0 for false and 1 for true values.


assert_eq!(u16::from(true), 1);
assert_eq!(u16::from(false), 0);Run

impl From<bool> for u32[src]

Converts a bool to a u32. The resulting value is 0 for false and 1 for true values.


assert_eq!(u32::from(true), 1);
assert_eq!(u32::from(false), 0);Run

impl From<bool> for u64[src]

Converts a bool to a u64. The resulting value is 0 for false and 1 for true values.


assert_eq!(u64::from(true), 1);
assert_eq!(u64::from(false), 0);Run

impl From<bool> for u128[src]

Converts a bool to a u128. The resulting value is 0 for false and 1 for true values.


assert_eq!(u128::from(true), 1);
assert_eq!(u128::from(false), 0);Run

impl From<bool> for usize[src]

Converts a bool to a usize. The resulting value is 0 for false and 1 for true values.


assert_eq!(usize::from(true), 1);
assert_eq!(usize::from(false), 0);Run

impl From<char> for u32[src]

fn from(c: char) -> Self[src]

Converts a char into a u32.


use std::mem;

fn main() {
    let c = 'c';
    let u = u32::from(c);
    assert!(4 == mem::size_of_val(&u))

impl From<f32> for f64[src]

Converts f32 to f64 losslessly.

impl From<i8> for isize[src]

Converts i8 to isize losslessly.

impl From<i16> for isize[src]

Converts i16 to isize losslessly.

impl From<i16> for AtomicI16[src]

fn from(v: i16) -> Self[src]

Converts an i16 into an AtomicI16.

impl From<i16> for f32[src]

Converts i16 to f32 losslessly.

impl From<i16> for f64[src]

Converts i16 to f64 losslessly.

impl From<i16> for i32[src]

Converts i16 to i32 losslessly.

impl From<i16> for i64[src]

Converts i16 to i64 losslessly.

impl From<i16> for i128[src]

Converts i16 to i128 losslessly.

impl From<i32> for AtomicI32[src]

fn from(v: i32) -> Self[src]

Converts an i32 into an AtomicI32.

impl From<i32> for f64[src]

Converts i32 to f64 losslessly.

impl From<i32> for i64[src]

Converts i32 to i64 losslessly.

impl From<i32> for i128[src]

Converts i32 to i128 losslessly.

impl From<i64> for AtomicI64[src]

fn from(v: i64) -> Self[src]

Converts an i64 into an AtomicI64.

impl From<i64> for i128[src]

Converts i64 to i128 losslessly.

impl From<i8> for AtomicI8[src]

fn from(v: i8) -> Self[src]

Converts an i8 into an AtomicI8.

impl From<i8> for f32[src]

Converts i8 to f32 losslessly.

impl From<i8> for f64[src]

Converts i8 to f64 losslessly.

impl From<i8> for i16[src]

Converts i8 to i16 losslessly.

impl From<i8> for i32[src]

Converts i8 to i32 losslessly.

impl From<i8> for i64[src]

Converts i8 to i64 losslessly.

impl From<i8> for i128[src]

Converts i8 to i128 losslessly.

impl From<isize> for AtomicIsize[src]

fn from(v: isize) -> Self[src]

Converts an isize into an AtomicIsize.

impl From<u8> for usize[src]

Converts u8 to usize losslessly.

impl From<u8> for isize[src]

Converts u8 to isize losslessly.

impl From<u8> for char[src]

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

fn from(i: u8) -> Self[src]

Converts a u8 into a char.


use std::mem;

fn main() {
    let u = 32 as u8;
    let c = char::from(u);
    assert!(4 == mem::size_of_val(&c))

impl From<u16> for usize[src]

Converts u16 to usize losslessly.

impl From<u16> for AtomicU16[src]

fn from(v: u16) -> Self[src]

Converts an u16 into an AtomicU16.

impl From<u16> for f32[src]

Converts u16 to f32 losslessly.

impl From<u16> for f64[src]

Converts u16 to f64 losslessly.

impl From<u16> for i32[src]

Converts u16 to i32 losslessly.

impl From<u16> for i64[src]

Converts u16 to i64 losslessly.

impl From<u16> for i128[src]

Converts u16 to i128 losslessly.

impl From<u16> for u32[src]

Converts u16 to u32 losslessly.

impl From<u16> for u64[src]

Converts u16 to u64 losslessly.

impl From<u16> for u128[src]

Converts u16 to u128 losslessly.

impl From<u32> for AtomicU32[src]

fn from(v: u32) -> Self[src]

Converts an u32 into an AtomicU32.

impl From<u32> for f64[src]

Converts u32 to f64 losslessly.

impl From<u32> for i64[src]

Converts u32 to i64 losslessly.

impl From<u32> for i128[src]

Converts u32 to i128 losslessly.

impl From<u32> for u64[src]

Converts u32 to u64 losslessly.

impl From<u32> for u128[src]

Converts u32 to u128 losslessly.

impl From<u64> for AtomicU64[src]

fn from(v: u64) -> Self[src]

Converts an u64 into an AtomicU64.

impl From<u64> for i128[src]

Converts u64 to i128 losslessly.

impl From<u64> for u128[src]

Converts u64 to u128 losslessly.

impl From<u8> for AtomicU8[src]

fn from(v: u8) -> Self[src]

Converts an u8 into an AtomicU8.

impl From<u8> for f32[src]

Converts u8 to f32 losslessly.

impl From<u8> for f64[src]

Converts u8 to f64 losslessly.

impl From<u8> for i16[src]

Converts u8 to i16 losslessly.

impl From<u8> for i32[src]

Converts u8 to i32 losslessly.

impl From<u8> for i64[src]

Converts u8 to i64 losslessly.

impl From<u8> for i128[src]

Converts u8 to i128 losslessly.

impl From<u8> for u16[src]

Converts u8 to u16 losslessly.

impl From<u8> for u32[src]

Converts u8 to u32 losslessly.

impl From<u8> for u64[src]

Converts u8 to u64 losslessly.

impl From<u8> for u128[src]

Converts u8 to u128 losslessly.

impl From<usize> for AtomicUsize[src]

fn from(v: usize) -> Self[src]

Converts an usize into an AtomicUsize.

impl<'a, T> From<&'a Option<T>> for Option<&'a T>[src]

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

impl<'a, T: ?Sized> From<&'a T> for NonNull<T>[src]

impl<'a, T: ?Sized> From<&'a mut T> for NonNull<T>[src]

impl<T> From<*mut T> for AtomicPtr<T>[src]

impl<T> From<T> for Option<T>[src]

impl<T> From<T> for Poll<T>[src]

impl<T> From<T> for Cell<T>[src]

impl<T> From<T> for RefCell<T>[src]

impl<T> From<T> for UnsafeCell<T>[src]

impl<T> From<T> for T[src]

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