Trait tear::From

pub trait From<T> {
#[lang = "from"]    pub fn from(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. If the conversion can fail, 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

#[lang = "from"]pub fn from(T) -> Self

Performs the conversion.

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Implementations on Foreign Types

impl From<NonZeroU8> for NonZeroI128

Converts NonZeroU8 to NonZeroI128 losslessly.

pub fn from(small: NonZeroU8) -> NonZeroI128

impl From<NonZeroU32> for NonZeroI128

Converts NonZeroU32 to NonZeroI128 losslessly.

pub fn from(small: NonZeroU32) -> NonZeroI128

impl From<NonZeroU16> for NonZeroU32

Converts NonZeroU16 to NonZeroU32 losslessly.

pub fn from(small: NonZeroU16) -> NonZeroU32

impl From<NonZeroU32> for NonZeroI64

Converts NonZeroU32 to NonZeroI64 losslessly.

pub fn from(small: NonZeroU32) -> NonZeroI64

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

pub fn from(t: T) -> Cell<T>

impl<'_, T> From<&'_ T> for NonNull<T> where
    T: ?Sized, 

pub fn from(reference: &T) -> NonNull<T>

impl From<u32> for AtomicU32

pub fn from(v: u32) -> AtomicU32

Converts an u32 into an AtomicU32.

impl From<NonZeroU64> for NonZeroI128

Converts NonZeroU64 to NonZeroI128 losslessly.

pub fn from(small: NonZeroU64) -> NonZeroI128

impl From<i64> for AtomicI64

pub fn from(v: i64) -> AtomicI64

Converts an i64 into an AtomicI64.

impl From<u8> for AtomicU8

pub fn from(v: u8) -> AtomicU8

Converts an u8 into an AtomicU8.

impl From<u64> for AtomicU64

pub fn from(v: u64) -> AtomicU64

Converts an u64 into an AtomicU64.

impl From<NonZeroU8> for NonZeroUsize

Converts NonZeroU8 to NonZeroUsize losslessly.

pub fn from(small: NonZeroU8) -> NonZeroUsize

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

pub fn from(t: T) -> UnsafeCell<T>

impl From<NonZeroI8> for NonZeroIsize

Converts NonZeroI8 to NonZeroIsize losslessly.

pub fn from(small: NonZeroI8) -> NonZeroIsize

impl From<NonZeroI16> for NonZeroI32

Converts NonZeroI16 to NonZeroI32 losslessly.

pub fn from(small: NonZeroI16) -> NonZeroI32

impl From<NonZeroI8> for NonZeroI16

Converts NonZeroI8 to NonZeroI16 losslessly.

pub fn from(small: NonZeroI8) -> NonZeroI16

impl From<NonZeroU8> for NonZeroU16

Converts NonZeroU8 to NonZeroU16 losslessly.

pub fn from(small: NonZeroU8) -> NonZeroU16

impl From<NonZeroU16> for NonZeroU128

Converts NonZeroU16 to NonZeroU128 losslessly.

pub fn from(small: NonZeroU16) -> NonZeroU128

impl From<NonZeroU16> for NonZeroI64

Converts NonZeroU16 to NonZeroI64 losslessly.

pub fn from(small: NonZeroU16) -> NonZeroI64

impl From<NonZeroU8> for NonZeroU32

Converts NonZeroU8 to NonZeroU32 losslessly.

pub fn from(small: NonZeroU8) -> NonZeroU32

impl From<Infallible> for TryFromIntError

pub fn from(x: Infallible) -> TryFromIntError

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

pub fn from(p: *mut T) -> AtomicPtr<T>

impl From<i32> for AtomicI32

pub fn from(v: i32) -> AtomicI32

Converts an i32 into an AtomicI32.

impl<'_, T> From<&'_ mut T> for NonNull<T> where
    T: ?Sized, 

pub fn from(reference: &mut T) -> NonNull<T>

impl From<NonZeroU16> for NonZeroUsize

Converts NonZeroU16 to NonZeroUsize losslessly.

pub fn from(small: NonZeroU16) -> NonZeroUsize

impl From<NonZeroI32> for NonZeroI64

Converts NonZeroI32 to NonZeroI64 losslessly.

pub fn from(small: NonZeroI32) -> NonZeroI64

impl From<NonZeroU16> for NonZeroI128

Converts NonZeroU16 to NonZeroI128 losslessly.

pub fn from(small: NonZeroU16) -> NonZeroI128

impl From<NonZeroI64> for NonZeroI128

Converts NonZeroI64 to NonZeroI128 losslessly.

pub fn from(small: NonZeroI64) -> NonZeroI128

impl From<NonZeroU8> for NonZeroU64

Converts NonZeroU8 to NonZeroU64 losslessly.

pub fn from(small: NonZeroU8) -> NonZeroU64

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

pub fn from(val: T) -> Option<T>

Copies val into a new Some.

Examples

let o: Option<u8> = Option::from(67);

assert_eq!(Some(67), o);

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

pub fn from(o: &'a Option<T>) -> Option<&'a T>

Converts from &Option<T> to Option<&T>.

Examples

Converts an Option<String> into an Option<usize>, preserving the original. The map method takes the self argument by value, consuming the original, so this technique uses as_ref to first take an Option to a reference to the value inside the original.

let s: Option<String> = Some(String::from("Hello, Rustaceans!"));
let o: Option<usize> = Option::from(&s).map(|ss: &String| ss.len());

println!("Can still print s: {:?}", s);

assert_eq!(o, Some(18));

impl From<NonZeroU64> for NonZeroU128

Converts NonZeroU64 to NonZeroU128 losslessly.

pub fn from(small: NonZeroU64) -> NonZeroU128

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

pub fn from(o: &'a mut Option<T>) -> Option<&'a mut T>

Converts from &mut Option<T> to Option<&mut T>

Examples

let mut s = Some(String::from("Hello"));
let o: Option<&mut String> = Option::from(&mut s);

match o {
    Some(t) => *t = String::from("Hello, Rustaceans!"),
    None => (),
}

assert_eq!(s, Some(String::from("Hello, Rustaceans!")));

impl From<i8> for AtomicI8

pub fn from(v: i8) -> AtomicI8

Converts an i8 into an AtomicI8.

impl From<NonZeroU8> for NonZeroI64

Converts NonZeroU8 to NonZeroI64 losslessly.

pub fn from(small: NonZeroU8) -> NonZeroI64

impl From<u16> for AtomicU16

pub fn from(v: u16) -> AtomicU16

Converts an u16 into an AtomicU16.

impl<T> From<Unique<T>> for NonNull<T> where
    T: ?Sized, 

pub fn from(unique: Unique<T>) -> NonNull<T>

impl From<!> for TryFromIntError

pub fn from(never: !) -> TryFromIntError

impl From<NonZeroU32> for NonZeroU128

Converts NonZeroU32 to NonZeroU128 losslessly.

pub fn from(small: NonZeroU32) -> NonZeroU128

impl From<NonZeroI16> for NonZeroIsize

Converts NonZeroI16 to NonZeroIsize losslessly.

pub fn from(small: NonZeroI16) -> NonZeroIsize

impl From<i16> for AtomicI16

pub fn from(v: i16) -> AtomicI16

Converts an i16 into an AtomicI16.

impl From<usize> for AtomicUsize

pub fn from(v: usize) -> AtomicUsize

Converts an usize into an AtomicUsize.

impl From<isize> for AtomicIsize

pub fn from(v: isize) -> AtomicIsize

Converts an isize into an AtomicIsize.

impl From<NonZeroI32> for NonZeroI128

Converts NonZeroI32 to NonZeroI128 losslessly.

pub fn from(small: NonZeroI32) -> NonZeroI128

impl From<NonZeroU8> for NonZeroI32

Converts NonZeroU8 to NonZeroI32 losslessly.

pub fn from(small: NonZeroU8) -> NonZeroI32

impl From<NonZeroU16> for NonZeroI32

Converts NonZeroU16 to NonZeroI32 losslessly.

pub fn from(small: NonZeroU16) -> NonZeroI32

impl From<!> for Infallible

pub fn from(x: !) -> Infallible

impl From<NonZeroU8> for NonZeroI16

Converts NonZeroU8 to NonZeroI16 losslessly.

pub fn from(small: NonZeroU8) -> NonZeroI16

impl From<Infallible> for TryFromSliceError

pub fn from(x: Infallible) -> TryFromSliceError

impl From<NonZeroU8> for NonZeroIsize

Converts NonZeroU8 to NonZeroIsize losslessly.

pub fn from(small: NonZeroU8) -> NonZeroIsize

impl From<NonZeroI8> for NonZeroI128

Converts NonZeroI8 to NonZeroI128 losslessly.

pub fn from(small: NonZeroI8) -> NonZeroI128

impl From<NonZeroI8> for NonZeroI64

Converts NonZeroI8 to NonZeroI64 losslessly.

pub fn from(small: NonZeroI8) -> NonZeroI64

impl From<NonZeroI8> for NonZeroI32

Converts NonZeroI8 to NonZeroI32 losslessly.

pub fn from(small: NonZeroI8) -> NonZeroI32

impl From<NonZeroU8> for NonZeroU128

Converts NonZeroU8 to NonZeroU128 losslessly.

pub fn from(small: NonZeroU8) -> NonZeroU128

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

pub fn from(t: T) -> Poll<T>

Convert to a Ready variant.

Example

assert_eq!(Poll::from(true), Poll::Ready(true));

impl From<NonZeroU16> for NonZeroU64

Converts NonZeroU16 to NonZeroU64 losslessly.

pub fn from(small: NonZeroU16) -> NonZeroU64

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

pub fn from(t: T) -> RefCell<T>

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

pub fn from(value: T) -> OnceCell<T>

impl From<bool> for AtomicBool

pub fn from(b: bool) -> AtomicBool

Converts a bool into an AtomicBool.

Examples

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

impl From<NonZeroU32> for NonZeroU64

Converts NonZeroU32 to NonZeroU64 losslessly.

pub fn from(small: NonZeroU32) -> NonZeroU64

impl From<NonZeroI16> for NonZeroI64

Converts NonZeroI16 to NonZeroI64 losslessly.

pub fn from(small: NonZeroI16) -> NonZeroI64

impl From<NonZeroI16> for NonZeroI128

Converts NonZeroI16 to NonZeroI128 losslessly.

pub fn from(small: NonZeroI16) -> NonZeroI128

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Implementors

impl From<()> for Maru

fn from(_: ()) -> Self

impl From<Maru> for ()

fn from(_: Maru)

impl From<NonZeroI8> for i8

pub fn from(nonzero: NonZeroI8) -> i8

Converts a NonZeroI8 into an i8

impl From<NonZeroI16> for i16

pub fn from(nonzero: NonZeroI16) -> i16

Converts a NonZeroI16 into an i16

impl From<NonZeroI32> for i32

pub fn from(nonzero: NonZeroI32) -> i32

Converts a NonZeroI32 into an i32

impl From<NonZeroI64> for i64

pub fn from(nonzero: NonZeroI64) -> i64

Converts a NonZeroI64 into an i64

impl From<NonZeroI128> for i128

pub fn from(nonzero: NonZeroI128) -> i128

Converts a NonZeroI128 into an i128

impl From<NonZeroIsize> for isize

pub fn from(nonzero: NonZeroIsize) -> isize

Converts a NonZeroIsize into an isize

impl From<NonZeroU8> for u8

pub fn from(nonzero: NonZeroU8) -> u8

Converts a NonZeroU8 into an u8

impl From<NonZeroU16> for u16

pub fn from(nonzero: NonZeroU16) -> u16

Converts a NonZeroU16 into an u16

impl From<NonZeroU32> for u32

pub fn from(nonzero: NonZeroU32) -> u32

Converts a NonZeroU32 into an u32

impl From<NonZeroU64> for u64

pub fn from(nonzero: NonZeroU64) -> u64

Converts a NonZeroU64 into an u64

impl From<NonZeroU128> for u128

pub fn from(nonzero: NonZeroU128) -> u128

Converts a NonZeroU128 into an u128

impl From<NonZeroUsize> for usize

pub fn from(nonzero: NonZeroUsize) -> usize

Converts a NonZeroUsize into an usize

impl From<bool> for i8

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

Examples

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

pub fn from(small: bool) -> i8

impl From<bool> for i16

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

Examples

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

pub fn from(small: bool) -> i16

impl From<bool> for i32

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

Examples

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

pub fn from(small: bool) -> i32

impl From<bool> for i64

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

Examples

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

pub fn from(small: bool) -> i64

impl From<bool> for i128

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

Examples

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

pub fn from(small: bool) -> i128

impl From<bool> for isize

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

Examples

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

pub fn from(small: bool) -> isize

impl From<bool> for u8

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

Examples

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

pub fn from(small: bool) -> u8

impl From<bool> for u16

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

Examples

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

pub fn from(small: bool) -> u16

impl From<bool> for u32

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

Examples

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

pub fn from(small: bool) -> u32

impl From<bool> for u64

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

Examples

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

pub fn from(small: bool) -> u64

impl From<bool> for u128

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

Examples

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

pub fn from(small: bool) -> u128

impl From<bool> for usize

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

Examples

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

pub fn from(small: bool) -> usize

impl From<char> for u32

pub fn from(c: char) -> u32

Converts a char into a u32.

Examples

use std::mem;

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

impl From<char> for u64

pub fn from(c: char) -> u64

Converts a char into a u64.

Examples

use std::mem;

let c = '👤';
let u = u64::from(c);
assert!(8 == mem::size_of_val(&u))

impl From<char> for u128

pub fn from(c: char) -> u128

Converts a char into a u128.

Examples

use std::mem;

let c = '⚙';
let u = u128::from(c);
assert!(16 == mem::size_of_val(&u))

impl From<f32> for f64

Converts f32 to f64 losslessly.

pub fn from(small: f32) -> f64

impl From<i8> for f32

Converts i8 to f32 losslessly.

pub fn from(small: i8) -> f32

impl From<i8> for f64

Converts i8 to f64 losslessly.

pub fn from(small: i8) -> f64

impl From<i8> for i16

Converts i8 to i16 losslessly.

pub fn from(small: i8) -> i16

impl From<i8> for i32

Converts i8 to i32 losslessly.

pub fn from(small: i8) -> i32

impl From<i8> for i64

Converts i8 to i64 losslessly.

pub fn from(small: i8) -> i64

impl From<i8> for i128

Converts i8 to i128 losslessly.

pub fn from(small: i8) -> i128

impl From<i8> for isize

Converts i8 to isize losslessly.

pub fn from(small: i8) -> isize

impl From<i16> for f32

Converts i16 to f32 losslessly.

pub fn from(small: i16) -> f32

impl From<i16> for f64

Converts i16 to f64 losslessly.

pub fn from(small: i16) -> f64

impl From<i16> for i32

Converts i16 to i32 losslessly.

pub fn from(small: i16) -> i32

impl From<i16> for i64

Converts i16 to i64 losslessly.

pub fn from(small: i16) -> i64

impl From<i16> for i128

Converts i16 to i128 losslessly.

pub fn from(small: i16) -> i128

impl From<i16> for isize

Converts i16 to isize losslessly.

pub fn from(small: i16) -> isize

impl From<i32> for f64

Converts i32 to f64 losslessly.

pub fn from(small: i32) -> f64

impl From<i32> for i64

Converts i32 to i64 losslessly.

pub fn from(small: i32) -> i64

impl From<i32> for i128

Converts i32 to i128 losslessly.

pub fn from(small: i32) -> i128

impl From<i64> for i128

Converts i64 to i128 losslessly.

pub fn from(small: i64) -> i128

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.

pub fn from(i: u8) -> char

Converts a u8 into a char.

Examples

use std::mem;

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

impl From<u8> for f32

Converts u8 to f32 losslessly.

pub fn from(small: u8) -> f32

impl From<u8> for f64

Converts u8 to f64 losslessly.

pub fn from(small: u8) -> f64

impl From<u8> for i16

Converts u8 to i16 losslessly.

pub fn from(small: u8) -> i16

impl From<u8> for i32

Converts u8 to i32 losslessly.

pub fn from(small: u8) -> i32

impl From<u8> for i64

Converts u8 to i64 losslessly.

pub fn from(small: u8) -> i64

impl From<u8> for i128

Converts u8 to i128 losslessly.

pub fn from(small: u8) -> i128

impl From<u8> for isize

Converts u8 to isize losslessly.

pub fn from(small: u8) -> isize

impl From<u8> for u16

Converts u8 to u16 losslessly.

pub fn from(small: u8) -> u16

impl From<u8> for u32

Converts u8 to u32 losslessly.

pub fn from(small: u8) -> u32

impl From<u8> for u64

Converts u8 to u64 losslessly.

pub fn from(small: u8) -> u64

impl From<u8> for u128

Converts u8 to u128 losslessly.

pub fn from(small: u8) -> u128

impl From<u8> for usize

Converts u8 to usize losslessly.

pub fn from(small: u8) -> usize

impl From<u16> for f32

Converts u16 to f32 losslessly.

pub fn from(small: u16) -> f32

impl From<u16> for f64

Converts u16 to f64 losslessly.

pub fn from(small: u16) -> f64

impl From<u16> for i32

Converts u16 to i32 losslessly.

pub fn from(small: u16) -> i32

impl From<u16> for i64

Converts u16 to i64 losslessly.

pub fn from(small: u16) -> i64

impl From<u16> for i128

Converts u16 to i128 losslessly.

pub fn from(small: u16) -> i128

impl From<u16> for u32

Converts u16 to u32 losslessly.

pub fn from(small: u16) -> u32

impl From<u16> for u64

Converts u16 to u64 losslessly.

pub fn from(small: u16) -> u64

impl From<u16> for u128

Converts u16 to u128 losslessly.

pub fn from(small: u16) -> u128

impl From<u16> for usize

Converts u16 to usize losslessly.

pub fn from(small: u16) -> usize

impl From<u32> for f64

Converts u32 to f64 losslessly.

pub fn from(small: u32) -> f64

impl From<u32> for i64

Converts u32 to i64 losslessly.

pub fn from(small: u32) -> i64

impl From<u32> for i128

Converts u32 to i128 losslessly.

pub fn from(small: u32) -> i128

impl From<u32> for u64

Converts u32 to u64 losslessly.

pub fn from(small: u32) -> u64

impl From<u32> for u128

Converts u32 to u128 losslessly.

pub fn from(small: u32) -> u128

impl From<u64> for i128

Converts u64 to i128 losslessly.

pub fn from(small: u64) -> i128

impl From<u64> for u128

Converts u64 to u128 losslessly.

pub fn from(small: u64) -> u128

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.

pub fn from(t: !) -> T

impl<T> From<T> for T

pub fn from(t: T) -> T

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