Trait nom::lib::std::prelude::v1::rust_2015::From 1.0.0[−][src]
pub trait From<T> {
fn from(T) -> Self;
}Expand description
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 UimpliesInto<U> for TFromis reflexive, which means thatFrom<T> for Tis 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
Implementations on Foreign Types
Creates an IpAddr::V6 from an eight element 16-bit array.
Examples
use std::net::{IpAddr, Ipv6Addr};
let addr = IpAddr::from([
525u16, 524u16, 523u16, 522u16,
521u16, 520u16, 519u16, 518u16,
]);
assert_eq!(
IpAddr::V6(Ipv6Addr::new(
0x20d, 0x20c,
0x20b, 0x20a,
0x209, 0x208,
0x207, 0x206
)),
addr
);Converts a RecvError into a RecvTimeoutError.
This conversion always returns RecvTimeoutError::Disconnected.
No data is allocated on the heap.
Creates an Ipv6Addr from an eight element 16-bit array.
Examples
use std::net::Ipv6Addr;
let addr = Ipv6Addr::from([
525u16, 524u16, 523u16, 522u16,
521u16, 520u16, 519u16, 518u16,
]);
assert_eq!(
Ipv6Addr::new(
0x20d, 0x20c,
0x20b, 0x20a,
0x209, 0x208,
0x207, 0x206
),
addr
);Converts a RecvError into a TryRecvError.
This conversion always returns TryRecvError::Disconnected.
No data is allocated on the heap.
Converts a SocketAddrV6 into a SocketAddr::V6.
Creates a new instance of an RwLock<T> which is unlocked.
This is equivalent to RwLock::new.
Converts a ChildStdout into a Stdio
Examples
ChildStdout will be converted to Stdio using Stdio::from under the hood.
use std::process::{Command, Stdio};
let hello = Command::new("echo")
.arg("Hello, world!")
.stdout(Stdio::piped())
.spawn()
.expect("failed echo command");
let reverse = Command::new("rev")
.stdin(hello.stdout.unwrap()) // Converted into a Stdio here
.output()
.expect("failed reverse command");
assert_eq!(reverse.stdout, b"!dlrow ,olleH\n");Create a new cell with its contents set to value.
Example
#![feature(once_cell)]
use std::lazy::SyncOnceCell;
let a = SyncOnceCell::from(3);
let b = SyncOnceCell::new();
b.set(3)?;
assert_eq!(a, b);
Ok(())Converts a File into a Stdio
Examples
File will be converted to Stdio using Stdio::from under the hood.
use std::fs::File;
use std::process::Command;
// With the `foo.txt` file containing `Hello, world!"
let file = File::open("foo.txt").unwrap();
let reverse = Command::new("rev")
.stdin(file) // Implicit File conversion into a Stdio
.output()
.expect("failed reverse command");
assert_eq!(reverse.stdout, b"!dlrow ,olleH");Converts a SendError<T> into a TrySendError<T>.
This conversion always returns a TrySendError::Disconnected containing the data in the SendError<T>.
No data is allocated on the heap.
Converts a tuple struct (Into<IpAddr>, u16) into a SocketAddr.
This conversion creates a SocketAddr::V4 for an IpAddr::V4
and creates a SocketAddr::V6 for an IpAddr::V6.
u16 is treated as port of the newly created SocketAddr.
Converts a SocketAddrV4 into a SocketAddr::V4.
Creates a new mutex in an unlocked state ready for use.
This is equivalent to Mutex::new.
Converts a ChildStderr into a Stdio
Examples
use std::process::{Command, Stdio};
let reverse = Command::new("rev")
.arg("non_existing_file.txt")
.stderr(Stdio::piped())
.spawn()
.expect("failed reverse command");
let cat = Command::new("cat")
.arg("-")
.stdin(reverse.stderr.unwrap()) // Converted into a Stdio here
.output()
.expect("failed echo command");
assert_eq!(
String::from_utf8_lossy(&cat.stdout),
"rev: cannot open non_existing_file.txt: No such file or directory\n"
);Intended for use for errors not exposed to the user, where allocating onto the heap (for normal construction via Error::new) is too costly.
Creates an Ipv6Addr from a sixteen element byte array.
Examples
use std::net::Ipv6Addr;
let addr = Ipv6Addr::from([
25u8, 24u8, 23u8, 22u8, 21u8, 20u8, 19u8, 18u8,
17u8, 16u8, 15u8, 14u8, 13u8, 12u8, 11u8, 10u8,
]);
assert_eq!(
Ipv6Addr::new(
0x1918, 0x1716,
0x1514, 0x1312,
0x1110, 0x0f0e,
0x0d0c, 0x0b0a
),
addr
);Creates an IpAddr::V6 from a sixteen element byte array.
Examples
use std::net::{IpAddr, Ipv6Addr};
let addr = IpAddr::from([
25u8, 24u8, 23u8, 22u8, 21u8, 20u8, 19u8, 18u8,
17u8, 16u8, 15u8, 14u8, 13u8, 12u8, 11u8, 10u8,
]);
assert_eq!(
IpAddr::V6(Ipv6Addr::new(
0x1918, 0x1716,
0x1514, 0x1312,
0x1110, 0x0f0e,
0x0d0c, 0x0b0a
)),
addr
);Converts a ChildStdin into a Stdio
Examples
ChildStdin will be converted to Stdio using Stdio::from under the hood.
use std::process::{Command, Stdio};
let reverse = Command::new("rev")
.stdin(Stdio::piped())
.spawn()
.expect("failed reverse command");
let _echo = Command::new("echo")
.arg("Hello, world!")
.stdout(reverse.stdin.unwrap()) // Converted into a Stdio here
.output()
.expect("failed echo command");
// "!dlrow ,olleH" echoed to consoleConverts NonZeroI16 to NonZeroIsize losslessly.
Converts a NonZeroUsize into an usize
Converts NonZeroI64 to NonZeroI128 losslessly.
Converts NonZeroI16 to NonZeroI64 losslessly.
Converts NonZeroU8 to NonZeroU128 losslessly.
Converts NonZeroI32 to NonZeroI64 losslessly.
Converts NonZeroU16 to NonZeroI32 losslessly.
Converts NonZeroU32 to NonZeroI128 losslessly.
Converts a NonZeroIsize into an isize
Converts a NonZeroU16 into an u16
Converts an usize into an AtomicUsize.
Converts NonZeroI32 to NonZeroI128 losslessly.
Converts NonZeroU8 to NonZeroU64 losslessly.
Converts NonZeroU16 to NonZeroU64 losslessly.
Converts NonZeroU8 to NonZeroI16 losslessly.
Converts NonZeroU8 to NonZeroI64 losslessly.
Converts NonZeroU16 to NonZeroU32 losslessly.
Converts NonZeroU8 to NonZeroIsize losslessly.
Converts NonZeroI8 to NonZeroIsize losslessly.
Converts a NonZeroU64 into an u64
Converts NonZeroU16 to NonZeroUsize losslessly.
Converts NonZeroU32 to NonZeroU128 losslessly.
Converts a NonZeroI64 into an i64
Converts a NonZeroU128 into an u128
Converts NonZeroU64 to NonZeroI128 losslessly.
Converts NonZeroI8 to NonZeroI64 losslessly.
Converts NonZeroU8 to NonZeroI32 losslessly.
Converts an isize into an AtomicIsize.
Converts a NonZeroI32 into an i32
Converts NonZeroU16 to NonZeroU128 losslessly.
Converts a NonZeroU32 into an u32
Maps a byte in 0x00..=0xFF to a char whose code point has the same value, in U+0000..=U+00FF.
Unicode is designed such that this effectively decodes bytes with the character encoding that IANA calls ISO-8859-1. This encoding is compatible with ASCII.
Note that this is different from ISO/IEC 8859-1 a.k.a. ISO 8859-1 (with one less hyphen), which leaves some “blanks”, byte values that are not assigned to any character. ISO-8859-1 (the IANA one) assigns them to the C0 and C1 control codes.
Note that this is also different from Windows-1252 a.k.a. code page 1252, which is a superset ISO/IEC 8859-1 that assigns some (not all!) blanks to punctuation and various Latin characters.
To confuse things further, on the Web
ascii, iso-8859-1, and windows-1252 are all aliases
for a superset of Windows-1252 that fills the remaining blanks with corresponding
C0 and C1 control codes.
Converts a NonZeroI128 into an i128
Converts NonZeroI16 to NonZeroI32 losslessly.
Converts a bool into an AtomicBool.
Examples
use std::sync::atomic::AtomicBool;
let atomic_bool = AtomicBool::from(true);
assert_eq!(format!("{:?}", atomic_bool), "true")Converts NonZeroU8 to NonZeroU16 losslessly.
Converts NonZeroI8 to NonZeroI16 losslessly.
Converts NonZeroI8 to NonZeroI128 losslessly.
Converts NonZeroU16 to NonZeroI128 losslessly.
Converts NonZeroU8 to NonZeroI128 losslessly.
Converts NonZeroU8 to NonZeroUsize losslessly.
Converts NonZeroI8 to NonZeroI32 losslessly.
Converts NonZeroU32 to NonZeroI64 losslessly.
Converts NonZeroU32 to NonZeroU64 losslessly.
Converts NonZeroU8 to NonZeroU32 losslessly.
Converts NonZeroU64 to NonZeroU128 losslessly.
Converts NonZeroU16 to NonZeroI64 losslessly.
Converts a NonZeroI16 into an i16
Converts NonZeroI16 to NonZeroI128 losslessly.
Create an ArrayVec from an array.
use arrayvec::ArrayVec;
let mut array = ArrayVec::from([1, 2, 3]);
assert_eq!(array.len(), 3);
assert_eq!(array.capacity(), 3);Implementors
impl<'a, E> From<E> for Box<dyn Error + Send + Sync + 'a, Global> where
E: 'a + Error + Send + Sync,
impl<'a, T> From<Cow<'a, [T]>> for Vec<T, Global> where
[T]: ToOwned,
<[T] as ToOwned>::Owned == Vec<T, Global>,
impl<K, V, const N: usize> From<[(K, V); N]> for HashMap<K, V, RandomState> where
K: Eq + Hash,
Stability note: This impl does not yet exist, but we are “reserving space” to add it in the future. See rust-lang/rust#64715 for details.