Trait std::convert::From 1.0.0
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[src]
pub trait From<T> {
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<'a, T> From<Vec<T>> for Cow<'a, [T]> where
T: Clone,impl<T> From<Vec<T>> for Box<[T]>impl<T> From<Vec<T>> for Rc<[T]>impl<'a> From<String> for Cow<'a, str>impl<T> From<Vec<T>> for Arc<[T]>impl From<Box<str>> for Stringimpl<'a, T> From<&'a [T]> for Arc<[T]> where
T: Clone,impl<'a> From<&'a str> for Arc<str>impl<'a> From<&'a str> for Stringimpl From<Box<str>> for Box<[u8]>impl<T> From<Box<T>> for Arc<T> where
T: ?Sized,impl<'a, T> From<&'a mut [T]> for Vec<T> where
T: Clone,impl<'a> From<&'a str> for Box<str>impl<'a> From<Cow<'a, str>> for Stringimpl From<String> for Box<str>impl<T> From<Vec<T>> for BinaryHeap<T> where
T: Ord,impl<'a, T> From<Cow<'a, [T]>> for Vec<T> where
[T]: ToOwned,
<[T] as ToOwned>::Owned == Vec<T>,impl<'a, T> From<&'a [T]> for Vec<T> where
T: Clone,impl<T> From<VecDeque<T>> for Vec<T>impl<'a> From<&'a str> for Cow<'a, str>impl<T> From<BinaryHeap<T>> for Vec<T>impl<T> From<Vec<T>> for VecDeque<T>impl<T> From<T> for Box<T>impl<T> From<Box<[T]>> for Vec<T>impl From<String> for Rc<str>impl From<String> for Vec<u8>impl<'a, T> From<&'a [T]> for Box<[T]> where
T: Copy,impl<T> From<Box<T>> for Rc<T> where
T: ?Sized,impl<'a> From<&'a str> for Rc<str>impl<'a, T> From<&'a [T]> for Cow<'a, [T]> where
T: Clone,impl<T> From<T> for Arc<T>impl<'a, T> From<&'a [T]> for Rc<[T]> where
T: Clone,impl<T> From<T> for Rc<T>impl From<String> for Arc<str>impl<'a> From<&'a str> for Vec<u8>impl From<u32> for f64impl From<u32> for u128impl<'a, T> From<&'a T> for Shared<T> where
T: ?Sized,impl From<u8> for u32impl From<u8> for u128impl From<u16> for u128impl<T> From<Unique<T>> for Shared<T> where
T: ?Sized,impl From<u8> for u16impl<'a, T> From<&'a T> for Unique<T> where
T: ?Sized,impl From<u64> for u128impl From<u16> for i128impl<'a, T> From<&'a mut T> for Unique<T> where
T: ?Sized,impl From<i16> for i64impl From<u32> for i64impl From<f32> for f64impl From<u8> for usizeimpl From<char> for u32impl<T> From<T> for Timpl From<u16> for f64impl From<u8> for i64impl From<u32> for i128impl<T> From<T> for UnsafeCell<T>impl From<i32> for i64impl From<u8> for f64impl From<i8> for isizeimpl From<i32> for i128impl From<i8> for i64impl From<u8> for charimpl<'a, T> From<&'a mut T> for NonZero<*mut T> where
T: ?Sized,impl From<u8> for i32impl<'a, T> From<&'a T> for NonZero<*const T> where
T: ?Sized,impl<'a, T> From<&'a mut T> for Shared<T> where
T: ?Sized,impl From<u8> for i128impl From<u16> for f32impl From<u16> for u64impl From<u8> for u64impl From<u16> for u32impl From<i16> for i128impl From<i16> for f32impl<T> From<T> for Option<T>impl From<i8> for i32impl From<i8> for i128impl From<u8> for i16impl From<u8> for f32impl From<i16> for i32impl From<u16> for i64impl<'a, T> From<&'a mut T> for NonZero<*const T> where
T: ?Sized,impl From<i8> for f64impl From<i64> for i128impl<T> From<T> for Cell<T>impl From<u32> for u64impl From<i32> for f64impl From<u16> for i32impl From<u64> for i128impl<T> From<T> for RefCell<T>impl From<i16> for f64impl From<i8> for f32impl From<i8> for i16impl<'a, E: Error + 'a> From<E> for Box<Error + 'a>impl<'a, E: Error + Send + Sync + 'a> From<E> for Box<Error + Send + Sync + 'a>impl From<String> for Box<Error + Send + Sync>impl From<String> for Box<Error>impl<'a, 'b> From<&'b str> for Box<Error + Send + Sync + 'a>impl<'a> From<&'a str> for Box<Error>impl From<CString> for Vec<u8>impl<'a> From<&'a CStr> for Box<CStr>impl From<Box<CStr>> for CStringimpl From<CString> for Box<CStr>impl From<NulError> for Errorimpl<'a> From<&'a CStr> for CStringimpl From<String> for OsStringimpl<'a, T: ?Sized + AsRef<OsStr>> From<&'a T> for OsStringimpl<'a> From<&'a OsStr> for Box<OsStr>impl From<Box<OsStr>> for OsStringimpl From<OsString> for Box<OsStr>impl<W> From<IntoInnerError<W>> for Errorimpl From<ErrorKind> for Errorimpl From<Ipv4Addr> for IpAddrimpl From<Ipv6Addr> for IpAddrimpl From<Ipv4Addr> for u32impl From<u32> for Ipv4Addrimpl From<[u8; 4]> for Ipv4Addrimpl From<[u8; 4]> for IpAddrimpl From<Ipv6Addr> for u128impl From<u128> for Ipv6Addrimpl From<[u8; 16]> for Ipv6Addrimpl From<[u16; 8]> for Ipv6Addrimpl From<[u8; 16]> for IpAddrimpl From<[u16; 8]> for IpAddrimpl From<SocketAddrV4> for SocketAddrimpl From<SocketAddrV6> for SocketAddrimpl<I: Into<IpAddr>> From<(I, u16)> for SocketAddrimpl<'a> From<&'a Path> for Box<Path>impl From<Box<Path>> for PathBufimpl From<PathBuf> for Box<Path>impl<'a, T: ?Sized + AsRef<OsStr>> From<&'a T> for PathBufimpl From<OsString> for PathBufimpl From<PathBuf> for OsStringimpl From<String> for PathBufimpl<'a> From<&'a Path> for Cow<'a, Path>impl<'a> From<PathBuf> for Cow<'a, Path>impl From<ChildStdin> for Stdioimpl From<ChildStdout> for Stdioimpl From<ChildStderr> for Stdioimpl From<File> for Stdioimpl<T> From<PoisonError<T>> for TryLockError<T>