Trait core::convert::From 1.0.0
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[src]
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
Examples
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::io::{self, Read}; 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 file = std::fs::File::open("test")?; let mut contents = String::new(); file.read_to_string(&mut contents)?; let num: i32 = contents.trim().parse()?; Ok(num) }Run
Required Methods
fn from(_: T) -> Self
Performs the conversion.
Implementors
impl From<Infallible> for TryFromIntErrorimpl From<u8> for u16impl From<u8> for u32impl From<u8> for u64impl From<u8> for u128impl From<u8> for usizeimpl From<u16> for u32impl From<u16> for u64impl From<u16> for u128impl From<u32> for u64impl From<u32> for u128impl From<u64> for u128impl From<i8> for i16impl From<i8> for i32impl From<i8> for i64impl From<i8> for i128impl From<i8> for isizeimpl From<i16> for i32impl From<i16> for i64impl From<i16> for i128impl From<i32> for i64impl From<i32> for i128impl From<i64> for i128impl From<u8> for i16impl From<u8> for i32impl From<u8> for i64impl From<u8> for i128impl From<u16> for i32impl From<u16> for i64impl From<u16> for i128impl From<u32> for i64impl From<u32> for i128impl From<u64> for i128impl From<i8> for f32impl From<i8> for f64impl From<i16> for f32impl From<i16> for f64impl From<i32> for f64impl From<u8> for f32impl From<u8> for f64impl From<u16> for f32impl From<u16> for f64impl From<u32> for f64impl From<f32> for f64impl<'a, T: ?Sized> From<&'a mut T> for NonZero<*mut T>impl<'a, T: ?Sized> From<&'a mut T> for NonZero<*const T>impl<'a, T: ?Sized> From<&'a T> for NonZero<*const T>impl<'a, T: ?Sized> From<&'a mut T> for Unique<T>impl<'a, T: ?Sized> From<&'a T> for Unique<T>impl<T: ?Sized> From<Unique<T>> for Shared<T>impl<'a, T: ?Sized> From<&'a mut T> for Shared<T>impl<'a, T: ?Sized> From<&'a T> for Shared<T>impl<T> From<T> for Timpl<T> From<*mut T> for AtomicPtr<T>impl From<i8> for AtomicI8impl From<u8> for AtomicU8impl From<i16> for AtomicI16impl From<u16> for AtomicU16impl From<i32> for AtomicI32impl From<u32> for AtomicU32impl From<i64> for AtomicI64impl From<u64> for AtomicU64impl From<isize> for AtomicIsizeimpl From<usize> for AtomicUsizeimpl<T> From<T> for Cell<T>impl<T> From<T> for RefCell<T>impl<T> From<T> for UnsafeCell<T>impl From<char> for u32impl From<u8> for charimpl<T> From<T> for Option<T>