Trait std::convert::From 1.0.0
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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.
Implementations on Foreign Types
impl<'a, T> From<&'a mut T> for NonZero<*mut T> where
T: ?Sized,
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T: ?Sized,
impl<'a, T> From<&'a T> for NonZero<*const T> where
T: ?Sized,
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T: ?Sized,
impl<'a, T> From<&'a mut T> for NonZero<*const T> where
T: ?Sized,
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T: ?Sized,
Implementors
impl From<u16> for u128
impl<'a, T> From<&'a T> for Unique<T> where
T: ?Sized,impl From<u8> for f32
impl From<i16> for f32
impl From<u16> for u32
impl From<u8> for f64
impl From<u8> for u32
impl From<u32> for u128
impl From<u16> for i128
impl<'a, T> From<NonNull<T>> for Unique<T> where
T: ?Sized,impl From<u16> for f32
impl From<i8> for i32
impl From<u32> for i64
impl From<u32> for AtomicU32
impl From<u8> for AtomicU8
impl From<f32> for f64
impl<'a, T> From<&'a T> for NonNull<T> where
T: ?Sized,impl<'a, T> From<&'a mut T> for NonNull<T> where
T: ?Sized,impl<T> From<*mut T> for AtomicPtr<T>
impl From<u32> for i128
impl From<i8> for i128
impl From<i32> for i64
impl From<i16> for AtomicI16
impl From<isize> for AtomicIsize
impl From<u64> for i128
impl<'a, T> From<&'a mut T> for Unique<T> where
T: ?Sized,impl From<u8> for i32
impl From<i64> for i128
impl<T> From<T> for T
impl From<Infallible> for TryFromIntError
impl From<u8> for u16
impl From<u8> for char
impl From<i64> for AtomicI64
impl From<bool> for AtomicBool
impl From<i8> for i16
impl From<u32> for u64
impl From<u8> for usize
impl From<i8> for f32
impl<T> From<T> for UnsafeCell<T>
impl From<u8> for u128
impl From<u32> for f64
impl<T> From<T> for Option<T>
impl From<i32> for i128
impl From<i8> for isize
impl From<i8> for AtomicI8
impl From<i8> for f64
impl From<u64> for AtomicU64
impl<T> From<Unique<T>> for NonNull<T> where
T: ?Sized,impl From<usize> for AtomicUsize
impl From<i16> for i128
impl From<i32> for AtomicI32
impl From<u16> for f64
impl From<u16> for i64
impl From<char> for u32
impl From<i16> for i32
impl From<u16> for i32
impl From<u8> for i64
impl From<i16> for f64
impl From<u8> for i128
impl From<i32> for f64
impl From<u8> for u64
impl From<u16> for AtomicU16
impl From<i16> for i64
impl From<u64> for u128
impl From<i8> for i64
impl<T> From<T> for RefCell<T>
impl From<u8> for i16
impl<T> From<T> for Cell<T>
impl From<u16> for u64
impl<'a> From<&'a str> for Rc<str>
impl<'a, T> From<&'a [T]> for Box<[T]> where
T: Copy,impl<'a> From<&'a str> for Box<str>
impl From<String> for Rc<str>
impl<T> From<T> for Arc<T>
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<Box<T>> for Rc<T> where
T: ?Sized,impl<T> From<Vec<T>> for BinaryHeap<T> where
T: Ord,impl<'a> From<&'a str> for Arc<str>
impl From<Box<str>> for Box<[u8]>
impl From<String> for Box<str>
impl From<String> for Arc<str>
impl From<Box<str>> for String
impl<T> From<T> for Rc<T>
impl<T> From<Box<[T]>> for Vec<T>
impl<'a> From<&'a str> for Cow<'a, str>
impl<'a, T> From<&'a [T]> for Cow<'a, [T]> where
T: Clone,impl<'a> From<&'a str> for String
impl<'a, T> From<Vec<T>> for Cow<'a, [T]> where
T: Clone,impl<T> From<T> for Box<T>
impl<T> From<VecDeque<T>> for Vec<T>
impl<T> From<Vec<T>> for Box<[T]>
impl<T> From<Box<T>> for Arc<T> where
T: ?Sized,impl<'a, T> From<&'a [T]> for Rc<[T]> where
T: Clone,impl<'a, T> From<&'a [T]> for Arc<[T]> where
T: Clone,impl From<String> for Vec<u8>
impl<T> From<Vec<T>> for Arc<[T]>
impl<'a> From<Cow<'a, str>> for String
impl<T> From<Vec<T>> for Rc<[T]>
impl<'a> From<&'a str> for Vec<u8>
impl<T> From<Vec<T>> for VecDeque<T>
impl<'a> From<String> for Cow<'a, str>
impl<T> From<BinaryHeap<T>> for Vec<T>
impl<'a, T> From<&'a mut [T]> for Vec<T> where
T: Clone,impl<'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<&'a CStr> for Box<CStr>
impl From<Box<CStr>> for CString
impl From<CString> for Box<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 Error
impl<'a> From<&'a CStr> for CString
impl From<String> for OsString
impl<'a, T: ?Sized + AsRef<OsStr>> From<&'a T> for OsString
impl<'a> From<&'a OsStr> for Box<OsStr>
impl From<Box<OsStr>> for OsString
impl 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<W> From<IntoInnerError<W>> for Error
impl From<ErrorKind> for Error
impl From<Ipv4Addr> for IpAddr
impl From<Ipv6Addr> for IpAddr
impl From<Ipv4Addr> for u32
impl From<u32> for Ipv4Addr
impl From<[u8; 4]> for Ipv4Addr
impl From<[u8; 4]> for IpAddr
impl From<Ipv6Addr> for u128
impl From<u128> for Ipv6Addr
impl From<[u8; 16]> for Ipv6Addr
impl From<[u16; 8]> for Ipv6Addr
impl From<[u8; 16]> for IpAddr
impl From<[u16; 8]> for IpAddr
impl From<SocketAddrV4> for SocketAddr
impl From<SocketAddrV6> for SocketAddr
impl<I: Into<IpAddr>> From<(I, u16)> for SocketAddr
impl<'a> From<&'a Path> for Box<Path>
impl From<Box<Path>> for PathBuf
impl From<PathBuf> for Box<Path>
impl<'a, T: ?Sized + AsRef<OsStr>> From<&'a T> for PathBuf
impl From<OsString> for PathBuf
impl From<PathBuf> for OsString
impl From<String> for PathBuf
impl<'a> From<&'a Path> for Cow<'a, Path>
impl<'a> From<PathBuf> for Cow<'a, Path>
impl 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 Stdio
impl From<ChildStdout> for Stdio
impl From<ChildStderr> for Stdio
impl From<File> for Stdio
impl<T> From<SendError<T>> for TrySendError<T>
impl From<RecvError> for TryRecvError
impl From<RecvError> for RecvTimeoutError
impl<T> From<T> for Mutex<T>
impl<T> From<T> for RwLock<T>
impl<T> From<PoisonError<T>> for TryLockError<T>