Trait nom::lib::std::convert::From1.0.0[−][src]

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`[src][−]

Performs the conversion.

Trait nom::lib::std::convert::From⎘1.0.0[−][src]

Generic Implementations

Examples

Required methods

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

Implementations on Foreign Types

impl From<Infallible> for TryFromSliceError[src][−]

pub fn from(x: Infallible) -> TryFromSliceError[src]

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

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

impl From<i32> for AtomicI32[src][−]

pub fn from(v: i32) -> AtomicI32[src][−]

impl From<NonZeroU32> for NonZeroU64[src][−]

pub fn from(small: NonZeroU32) -> NonZeroU64[src]

impl From<NonZeroU8> for NonZeroI128[src][−]

pub fn from(small: NonZeroU8) -> NonZeroI128[src]

impl<T> From<Unique<T>> for NonNull<T> where T: ?Sized, [src][−]

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

impl From<i8> for AtomicI8[src][−]

pub fn from(v: i8) -> AtomicI8[src][−]

impl From<NonZeroU64> for NonZeroI128[src][−]

pub fn from(small: NonZeroU64) -> NonZeroI128[src]

impl From<u8> for AtomicU8[src][−]

pub fn from(v: u8) -> AtomicU8[src][−]

impl From<NonZeroU8> for NonZeroUsize[src][−]

pub fn from(small: NonZeroU8) -> NonZeroUsize[src]

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

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

impl From<NonZeroU8> for NonZeroI32[src][−]

pub fn from(small: NonZeroU8) -> NonZeroI32[src]

impl From<NonZeroU8> for NonZeroU16[src][−]

pub fn from(small: NonZeroU8) -> NonZeroU16[src]

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

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

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

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

impl From<NonZeroI16> for NonZeroI128[src][−]

pub fn from(small: NonZeroI16) -> NonZeroI128[src]

impl From<NonZeroU16> for NonZeroI32[src][−]

pub fn from(small: NonZeroU16) -> NonZeroI32[src]

impl From<i64> for AtomicI64[src][−]

pub fn from(v: i64) -> AtomicI64[src][−]

impl From<NonZeroU8> for NonZeroU128[src][−]

pub fn from(small: NonZeroU8) -> NonZeroU128[src]

impl From<u16> for AtomicU16[src][−]

pub fn from(v: u16) -> AtomicU16[src][−]

impl From<usize> for AtomicUsize[src][−]

pub fn from(v: usize) -> AtomicUsize[src][−]

impl From<NonZeroI16> for NonZeroI32[src][−]

pub fn from(small: NonZeroI16) -> NonZeroI32[src]

impl From<NonZeroU64> for NonZeroU128[src][−]

pub fn from(small: NonZeroU64) -> NonZeroU128[src]

impl From<NonZeroU32> for NonZeroU128[src][−]

pub fn from(small: NonZeroU32) -> NonZeroU128[src]

impl From<NonZeroU16> for NonZeroU64[src][−]

pub fn from(small: NonZeroU16) -> NonZeroU64[src]

impl From<NonZeroI16> for NonZeroIsize[src][−]

pub fn from(small: NonZeroI16) -> NonZeroIsize[src]

impl From<NonZeroU8> for NonZeroU64[src][−]

pub fn from(small: NonZeroU8) -> NonZeroU64[src]

impl From<Infallible> for TryFromIntError[src][−]

pub fn from(x: Infallible) -> TryFromIntError[src]

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

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

impl<T> From<T> for Poll<T>[src][−]

pub fn from(t: T) -> Poll<T>[src][−]

Example

impl From<u32> for AtomicU32[src][−]

pub fn from(v: u32) -> AtomicU32[src][−]

impl From<NonZeroU8> for NonZeroU32[src][−]

pub fn from(small: NonZeroU8) -> NonZeroU32[src]

impl From<NonZeroU16> for NonZeroI64[src][−]

pub fn from(small: NonZeroU16) -> NonZeroI64[src]

impl From<NonZeroU32> for NonZeroI128[src][−]

pub fn from(small: NonZeroU32) -> NonZeroI128[src]

impl From<u64> for AtomicU64[src][−]

pub fn from(v: u64) -> AtomicU64[src][−]

impl From<NonZeroI8> for NonZeroIsize[src][−]

pub fn from(small: NonZeroI8) -> NonZeroIsize[src]

impl From<isize> for AtomicIsize[src][−]

Trait nom::lib::std::convert::From1.0.0[−][src]

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

`impl From<Infallible> for TryFromSliceError`[src][−]

`pub fn from(x: Infallible) -> TryFromSliceError`[src]

`impl<'_, T> From<&'_ mut T> for NonNull<T> where T: ?Sized,` [src][−]

`pub fn from(reference: &mut T) -> NonNull<T>`[src]

`impl From<i32> for AtomicI32`[src][−]

`pub fn from(v: i32) -> AtomicI32`[src][−]

`impl From<NonZeroU32> for NonZeroU64`[src][−]

`pub fn from(small: NonZeroU32) -> NonZeroU64`[src]

`impl From<NonZeroU8> for NonZeroI128`[src][−]

`pub fn from(small: NonZeroU8) -> NonZeroI128`[src]

`impl<T> From<Unique<T>> for NonNull<T> where T: ?Sized,` [src][−]

`pub fn from(unique: Unique<T>) -> NonNull<T>`[src]

`impl From<i8> for AtomicI8`[src][−]

`pub fn from(v: i8) -> AtomicI8`[src][−]

`impl From<NonZeroU64> for NonZeroI128`[src][−]

`pub fn from(small: NonZeroU64) -> NonZeroI128`[src]

`impl From<u8> for AtomicU8`[src][−]

`pub fn from(v: u8) -> AtomicU8`[src][−]

`impl From<NonZeroU8> for NonZeroUsize`[src][−]

`pub fn from(small: NonZeroU8) -> NonZeroUsize`[src]

`impl<'_, T> From<&'_ T> for NonNull<T> where T: ?Sized,` [src][−]

`pub fn from(reference: &T) -> NonNull<T>`[src]

`impl From<NonZeroU8> for NonZeroI32`[src][−]

`pub fn from(small: NonZeroU8) -> NonZeroI32`[src]

`impl From<NonZeroU8> for NonZeroU16`[src][−]

`pub fn from(small: NonZeroU8) -> NonZeroU16`[src]

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

`pub fn from(t: T) -> UnsafeCell<T>`[src]

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

`pub fn from(p: *mut T) -> AtomicPtr<T>`[src]

`impl From<NonZeroI16> for NonZeroI128`[src][−]

`pub fn from(small: NonZeroI16) -> NonZeroI128`[src]

`impl From<NonZeroU16> for NonZeroI32`[src][−]

`pub fn from(small: NonZeroU16) -> NonZeroI32`[src]

`impl From<i64> for AtomicI64`[src][−]

`pub fn from(v: i64) -> AtomicI64`[src][−]

`impl From<NonZeroU8> for NonZeroU128`[src][−]

`pub fn from(small: NonZeroU8) -> NonZeroU128`[src]

`impl From<u16> for AtomicU16`[src][−]

`pub fn from(v: u16) -> AtomicU16`[src][−]

`impl From<usize> for AtomicUsize`[src][−]

`pub fn from(v: usize) -> AtomicUsize`[src][−]

`impl From<NonZeroI16> for NonZeroI32`[src][−]

`pub fn from(small: NonZeroI16) -> NonZeroI32`[src]

`impl From<NonZeroU64> for NonZeroU128`[src][−]

`pub fn from(small: NonZeroU64) -> NonZeroU128`[src]

`impl From<NonZeroU32> for NonZeroU128`[src][−]

`pub fn from(small: NonZeroU32) -> NonZeroU128`[src]

`impl From<NonZeroU16> for NonZeroU64`[src][−]

`pub fn from(small: NonZeroU16) -> NonZeroU64`[src]

`impl From<NonZeroI16> for NonZeroIsize`[src][−]

`pub fn from(small: NonZeroI16) -> NonZeroIsize`[src]

`impl From<NonZeroU8> for NonZeroU64`[src][−]

`pub fn from(small: NonZeroU8) -> NonZeroU64`[src]

`impl From<Infallible> for TryFromIntError`[src][−]

`pub fn from(x: Infallible) -> TryFromIntError`[src]

`impl<T> From<T> for OnceCell<T>`[src][−]

`pub fn from(value: T) -> OnceCell<T>`[src]

`impl<T> From<T> for Poll<T>`[src][−]

`pub fn from(t: T) -> Poll<T>`[src][−]

`impl From<u32> for AtomicU32`[src][−]

`pub fn from(v: u32) -> AtomicU32`[src][−]

`impl From<NonZeroU8> for NonZeroU32`[src][−]

`pub fn from(small: NonZeroU8) -> NonZeroU32`[src]

`impl From<NonZeroU16> for NonZeroI64`[src][−]

`pub fn from(small: NonZeroU16) -> NonZeroI64`[src]

`impl From<NonZeroU32> for NonZeroI128`[src][−]

`pub fn from(small: NonZeroU32) -> NonZeroI128`[src]

`impl From<u64> for AtomicU64`[src][−]

`pub fn from(v: u64) -> AtomicU64`[src][−]

`impl From<NonZeroI8> for NonZeroIsize`[src][−]

`pub fn from(small: NonZeroI8) -> NonZeroIsize`[src]

`impl From<isize> for AtomicIsize`[src][−]

`pub fn from(v: isize) -> AtomicIsize`[src][−]

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

`pub fn from(t: T) -> RefCell<T>`[src]

`impl From<NonZeroI16> for NonZeroI64`[src][−]

`pub fn from(small: NonZeroI16) -> NonZeroI64`[src]