Trait std::convert::From 1.0.0[−][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 From<i16> for i32impl From<u8> for u32impl From<bool> for u32impl From<i8> for AtomicI8impl From<u8> for i32impl From<bool> for i32impl From<i8> for f32impl<T> From<T> for Poll<T>impl From<u8> for i16impl From<u8> for i64impl From<u32> for f64impl<'a, T> From<FutureObj<'a, T>> for LocalFutureObj<'a, T>impl From<bool> for u64impl<T> From<T> for Option<T>impl From<u16> for f32impl From<u8> for f32impl From<u32> for u64impl From<u8> for u64impl From<isize> for AtomicIsizeimpl From<i64> for AtomicI64impl From<i16> for i64impl<T> From<Unique<T>> for NonNull<T> where
T: ?Sized,impl<T> From<T> for RefCell<T>impl From<u64> for u128impl From<i32> for f64impl From<u8> for f64impl<T> From<*mut T> for AtomicPtr<T>impl From<bool> for u16impl From<i32> for i64impl From<char> for u32impl From<i8> for i32impl<T> From<T> for UnsafeCell<T>impl From<bool> for u8impl From<u16> for u64impl From<bool> for isizeimpl From<LocalWaker> for Wakerimpl From<u8> for usizeimpl From<i16> for f32impl<'a, T> From<&'a T> for NonNull<T> where
T: ?Sized,impl From<u32> for u128impl From<!> for TryFromIntErrorimpl From<u16> for i128impl From<usize> for AtomicUsizeimpl From<u8> for i128impl<'a, T> From<&'a mut T> for NonNull<T> where
T: ?Sized,impl From<u32> for i128impl From<i8> for f64impl From<i8> for i128impl From<bool> for i16impl From<u8> for AtomicU8impl From<u16> for u128impl From<i64> for i128impl From<i32> for AtomicI32impl From<i8> for i16impl From<u8> for charimpl From<u16> for AtomicU16impl From<bool> for AtomicBoolimpl From<u16> for usizeimpl<T> From<T> for Timpl From<i16> for i128impl From<u16> for i32impl From<bool> for i8impl From<u64> for AtomicU64impl From<u8> for u128impl From<u8> for u16impl From<u16> for u32impl<T> From<T> for Cell<T>impl From<i16> for isizeimpl From<i16> for f64impl From<i8> for isizeimpl From<u16> for i64impl From<bool> for i64impl From<f32> for f64impl From<u32> for i64impl From<bool> for usizeimpl From<bool> for u128impl From<i16> for AtomicI16impl From<u64> for i128impl From<bool> for i128impl From<i8> for i64impl From<u32> for AtomicU32impl From<u8> for isizeimpl From<i32> for i128impl From<u16> for f64impl<'a, F> From<PinBox<F>> for LocalFutureObj<'a, ()> where
F: 'a + Future<Output = ()>,impl<T> From<Box<T>> for PinBox<T> where
T: ?Sized,impl<T> From<BinaryHeap<T>> for Vec<T>impl<'a> From<&'a str> for Arc<str>impl From<Box<str>> for Box<[u8]>impl<T> From<T> for Rc<T>impl<T> From<Arc<T>> for Waker where
T: Wake + 'static,impl<'a, T> From<&'a [T]> for Vec<T> where
T: Clone,impl<'a, F> From<PinBox<F>> for FutureObj<'a, ()> where
F: 'a + Send + Future<Output = ()>,impl From<String> for Box<str>impl<'a, T> From<Vec<T>> for Cow<'a, [T]> where
T: Clone,impl<T> From<Vec<T>> for VecDeque<T>impl From<String> for Arc<str>impl<T> From<Vec<T>> for Box<[T]>impl<T> From<Vec<T>> for Arc<[T]>impl<T> From<T> for Box<T>impl<'a, T> From<&'a Vec<T>> for Cow<'a, [T]> where
T: Clone,impl<'a, T> From<&'a [T]> for Box<[T]> where
T: Copy,impl<'a> From<&'a String> for Cow<'a, str>impl<T> From<Box<T>> for Rc<T> where
T: ?Sized,impl<'a> From<String> for Cow<'a, str>impl<T> From<Box<[T]>> for Vec<T>impl From<LayoutErr> for CollectionAllocErrimpl<'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 Cow<'a, [T]> where
T: Clone,impl<'a, T> From<&'a [T]> for Rc<[T]> where
T: Clone,impl From<String> for Rc<str>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, F> From<Box<F>> for FutureObj<'a, ()> where
F: 'a + Send + Future<Output = ()>,impl<'a> From<&'a str> for Cow<'a, str>impl<'a, F> From<Box<F>> for LocalFutureObj<'a, ()> where
F: 'a + Future<Output = ()>,impl<T> From<VecDeque<T>> for Vec<T>impl<T> From<T> for Arc<T>impl<'a> From<&'a str> for Vec<u8>impl<'a> From<&'a str> for Rc<str>impl<'a, T> From<&'a [T]> for Arc<[T]> where
T: Clone,impl<'a> From<&'a str> for Stringimpl From<AllocErr> for CollectionAllocErrimpl From<Box<str>> for Stringimpl<'a> From<&'a str> for Box<str>impl From<String> for Vec<u8>impl<T> From<Vec<T>> for Rc<[T]>impl<T> From<PinBox<T>> for Box<T> where
T: Unpin + ?Sized,impl<T> From<Vec<T>> for BinaryHeap<T> where
T: Ord,impl<'a> From<Cow<'a, str>> for Stringimpl<'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<'a, 'b> From<Cow<'b, str>> for Box<Error + Send + Sync + 'a>impl<'a> From<Cow<'a, str>> for Box<Error>impl From<CString> for Vec<u8>impl<'a> From<Cow<'a, CStr>> for CStringimpl<'a> From<&'a CStr> for Box<CStr>impl From<Box<CStr>> for CStringimpl From<CString> for Box<CStr>impl<'a> From<CString> for Cow<'a, CStr>impl<'a> From<&'a CStr> for Cow<'a, CStr>impl<'a> From<&'a CString> for Cow<'a, CStr>impl From<CString> for Arc<CStr>impl<'a> From<&'a CStr> for Arc<CStr>impl From<CString> for Rc<CStr>impl<'a> From<&'a CStr> for Rc<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 From<OsString> for Arc<OsStr>impl<'a> From<&'a OsStr> for Arc<OsStr>impl From<OsString> for Rc<OsStr>impl<'a> From<&'a OsStr> for Rc<OsStr>impl<'a> From<OsString> for Cow<'a, OsStr>impl<'a> From<&'a OsStr> for Cow<'a, OsStr>impl<'a> From<&'a OsString> for Cow<'a, OsStr>impl<'a> From<Cow<'a, OsStr>> for OsStringimpl<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<'a> From<&'a PathBuf> for Cow<'a, Path>impl<'a> From<Cow<'a, Path>> for PathBufimpl From<PathBuf> for Arc<Path>impl<'a> From<&'a Path> for Arc<Path>impl From<PathBuf> for Rc<Path>impl<'a> From<&'a Path> for Rc<Path>impl From<ChildStdin> for Stdioimpl From<ChildStdout> for Stdioimpl From<ChildStderr> for Stdioimpl From<File> for Stdioimpl<T> From<SendError<T>> for TrySendError<T>impl From<RecvError> for TryRecvErrorimpl From<RecvError> for RecvTimeoutErrorimpl<T> From<T> for Mutex<T>impl<T> From<T> for RwLock<T>impl<T> From<PoisonError<T>> for TryLockError<T>