Trait nom::lib::std::convert::From1.0.0[−][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 U implies Into<U> for T
  • From is reflexive, which means that From<T> for T is 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

Performs the conversion.

Implementations on Foreign Types

Converts a SocketAddrV6 into a SocketAddr::V6.

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 String into an OsString.

This conversion does not allocate or copy memory.

Converts a borrowed OsStr to a PathBuf.

Allocates a PathBuf and copies the data into it.

Creates a new mutex in an unlocked state ready for use. This is equivalent to Mutex::new.

Copies this address to a new IpAddr::V4.

Examples
use std::net::{IpAddr, Ipv4Addr};

let addr = Ipv4Addr::new(127, 0, 0, 1);

assert_eq!(
    IpAddr::V4(addr),
    IpAddr::from(addr)
)

Converts a PathBuf into an Rc by moving the PathBuf data into a new Rc buffer.

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 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"
);

Converts a PathBuf into an Arc by moving the PathBuf data into a new Arc buffer.

Converts a NulError into a io::Error.

Converts a Vec<NonZeroU8> into a CString without copying nor checking for inner null bytes.

Converts an OsString into an Rc<OsStr> without copying or allocating.

Converts a Box<OsStr> into an OsString without copying or allocating.

Converts a RecvError into a TryRecvError.

This conversion always returns TryRecvError::Disconnected.

No data is allocated on the heap.

Converts a Box<Path> into a PathBuf

This conversion does not allocate or copy memory.

Converts a CString into an Rc<CStr> without copying or allocating.

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
);

Copies this address to a new IpAddr::V6.

Examples
use std::net::{IpAddr, Ipv6Addr};

let addr = Ipv6Addr::new(0, 0, 0, 0, 0, 0xffff, 0xc00a, 0x2ff);

assert_eq!(
    IpAddr::V6(addr),
    IpAddr::from(addr)
);

Converts an Ipv4Addr into a host byte order u32.

Examples
use std::net::Ipv4Addr;

let addr = Ipv4Addr::new(0xca, 0xfe, 0xba, 0xbe);
assert_eq!(0xcafebabe, u32::from(addr));

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 clone-on-write pointer to an owned path.

Converting from a Cow::Owned does not clone or allocate.

Creates an IpAddr::V4 from a four element byte array.

Examples
use std::net::{IpAddr, Ipv4Addr};

let addr = IpAddr::from([13u8, 12u8, 11u8, 10u8]);
assert_eq!(IpAddr::V4(Ipv4Addr::new(13, 12, 11, 10)), addr);

Intended for use for errors not exposed to the user, where allocating onto the heap (for normal construction via Error::new) is too costly.

Converts an ErrorKind into an Error.

This conversion allocates a new error with a simple representation of error kind.

Examples
use std::io::{Error, ErrorKind};

let not_found = ErrorKind::NotFound;
let error = Error::from(not_found);
assert_eq!("entity not found", format!("{}", error));

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 console

Converts an OsString into an Arc<OsStr> without copying or allocating.

Converts a Path into an Arc by copying the Path data into a new Arc buffer.

Creates a new instance of an RwLock<T> which is unlocked. This is equivalent to RwLock::new.

Convert a host byte order u128 into an Ipv6Addr.

Examples
use std::net::Ipv6Addr;

let addr = Ipv6Addr::from(0x102030405060708090A0B0C0D0E0F00D_u128);
assert_eq!(
    Ipv6Addr::new(
        0x1020, 0x3040, 0x5060, 0x7080,
        0x90A0, 0xB0C0, 0xD0E0, 0xF00D,
    ),
    addr);

Creates an Ipv4Addr from a four element byte array.

Examples
use std::net::Ipv4Addr;

let addr = Ipv4Addr::from([13u8, 12u8, 11u8, 10u8]);
assert_eq!(Ipv4Addr::new(13, 12, 11, 10), addr);

Converts a Path into an Rc by copying the Path data into a new Rc buffer.

Convert an Ipv6Addr into a host byte order u128.

Examples
use std::net::Ipv6Addr;

let addr = Ipv6Addr::new(
    0x1020, 0x3040, 0x5060, 0x7080,
    0x90A0, 0xB0C0, 0xD0E0, 0xF00D,
);
assert_eq!(0x102030405060708090A0B0C0D0E0F00D_u128, u128::from(addr));

Converts a host byte order u32 into an Ipv4Addr.

Examples
use std::net::Ipv4Addr;

let addr = Ipv4Addr::from(0xcafebabe);
assert_eq!(Ipv4Addr::new(0xca, 0xfe, 0xba, 0xbe), addr);

Converts a RecvError into a RecvTimeoutError.

This conversion always returns RecvTimeoutError::Disconnected.

No data is allocated on the heap.

Converts a CString into an Arc<CStr> without copying or allocating.

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(())

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
);

Converts a SocketAddrV4 into a SocketAddr::V4.

Converts a String into a PathBuf

This conversion does not allocate or copy memory.

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 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 Box<CStr> into a CString without copying or allocating.

Converts an OsString into a PathBuf

This conversion does not allocate or copy memory.

Converts a PathBuf into an OsString

This conversion does not allocate or copy memory.

Converts NonZeroI8 to NonZeroIsize losslessly.

Converts NonZeroI16 to NonZeroI64 losslessly.

Converts an u8 into an AtomicU8.

Converts NonZeroU32 to NonZeroU64 losslessly.

Converts NonZeroU16 to NonZeroU128 losslessly.

Converts NonZeroU16 to NonZeroI128 losslessly.

Converts a [char] into a [u64].

Examples
use std::mem;

let c = '👤';
let u = u64::from(c);
assert!(8 == mem::size_of_val(&u))

Converts u32 to u64 losslessly.

Converts i8 to i32 losslessly.

Converts a bool to a usize. The resulting value is 0 for false and 1 for true values.

Examples
assert_eq!(usize::from(true), 1);
assert_eq!(usize::from(false), 0);

Converts a [char] into a [u32].

Examples
use std::mem;

let c = 'c';
let u = u32::from(c);
assert!(4 == mem::size_of_val(&u))

Converts NonZeroU32 to NonZeroU128 losslessly.

Converts an u16 into an AtomicU16.

Converts a NonZeroUsize into an usize

Converts NonZeroI16 to NonZeroI128 losslessly.

Converts a NonZeroU16 into an u16

Converts an i16 into an AtomicI16.

Converts u64 to i128 losslessly.

Converts a bool to a isize. The resulting value is 0 for false and 1 for true values.

Examples
assert_eq!(isize::from(true), 1);
assert_eq!(isize::from(false), 0);

Converts an isize into an AtomicIsize.

Converts NonZeroI16 to NonZeroIsize losslessly.

Converts f32 to f64 losslessly.

Converts u8 to f32 losslessly.

Converts a NonZeroI32 into an i32

Converts a NonZeroIsize into an isize

Converts u16 to u64 losslessly.

Converts u8 to i128 losslessly.

Converts a bool to a u8. The resulting value is 0 for false and 1 for true values.

Examples
assert_eq!(u8::from(true), 1);
assert_eq!(u8::from(false), 0);

Converts a NonZeroU32 into an u32

Converts a bool to a u32. The resulting value is 0 for false and 1 for true values.

Examples
assert_eq!(u32::from(true), 1);
assert_eq!(u32::from(false), 0);

Converts u8 to i16 losslessly.

Converts u8 to u32 losslessly.

Converts u16 to i32 losslessly.

Converts i8 to f32 losslessly.

Converts a NonZeroI64 into an i64

Converts u32 to i64 losslessly.

Converts a NonZeroI16 into an i16

Converts an i32 into an AtomicI32.

Converts a [char] into a [u128].

Examples
use std::mem;

let c = '⚙';
let u = u128::from(c);
assert!(16 == mem::size_of_val(&u))

Converts NonZeroU8 to NonZeroI32 losslessly.

Converts i16 to f64 losslessly.

Converts i64 to i128 losslessly.

Converts i8 to i128 losslessly.

Converts NonZeroU16 to NonZeroI32 losslessly.

Converts NonZeroU64 to NonZeroI128 losslessly.

Converts i32 to f64 losslessly.

Converts i32 to i128 losslessly.

Converts NonZeroI8 to NonZeroI32 losslessly.

Converts u8 to u128 losslessly.

Converts a bool to a u128. The resulting value is 0 for false and 1 for true values.

Examples
assert_eq!(u128::from(true), 1);
assert_eq!(u128::from(false), 0);

Converts u32 to u128 losslessly.

Converts u16 to f32 losslessly.

Converts u8 to i32 losslessly.

Converts i8 to f64 losslessly.

Converts u8 to usize losslessly.

Converts NonZeroU8 to NonZeroU32 losslessly.

Converts an usize into an AtomicUsize.

Converts u16 to f64 losslessly.

Converts a bool to a i128. The resulting value is 0 for false and 1 for true values.

Examples
assert_eq!(i128::from(true), 1);
assert_eq!(i128::from(false), 0);

Converts u16 to u32 losslessly.

Converts a bool to a i16. The resulting value is 0 for false and 1 for true values.

Examples
assert_eq!(i16::from(true), 1);
assert_eq!(i16::from(false), 0);

Converts u8 to isize losslessly.

Converts NonZeroI64 to NonZeroI128 losslessly.

Converts an i8 into an AtomicI8.

Converts NonZeroI8 to NonZeroI64 losslessly.

Converts a bool to a i64. The resulting value is 0 for false and 1 for true values.

Examples
assert_eq!(i64::from(true), 1);
assert_eq!(i64::from(false), 0);

Converts u16 to u128 losslessly.

Converts u16 to i64 losslessly.

Converts i16 to isize losslessly.

Converts u32 to i128 losslessly.

Converts a bool to a u64. The resulting value is 0 for false and 1 for true values.

Examples
assert_eq!(u64::from(true), 1);
assert_eq!(u64::from(false), 0);

Converts a NonZeroU128 into an u128

Converts a NonZeroI128 into an i128

Converts a bool to a i32. The resulting value is 0 for false and 1 for true values.

Examples
assert_eq!(i32::from(true), 1);
assert_eq!(i32::from(false), 0);

Converts i8 to isize losslessly.

Converts NonZeroU8 to NonZeroI16 losslessly.

Converts an i64 into an AtomicI64.

Converts a NonZeroU8 into an u8

Converts a NonZeroU64 into an u64

Converts i16 to f32 losslessly.

Converts NonZeroU8 to NonZeroIsize losslessly.

Converts i8 to i16 losslessly.

Converts i8 to i64 losslessly.

Converts NonZeroU8 to NonZeroU64 losslessly.

Converts an u32 into an AtomicU32.

Converts an u64 into an AtomicU64.

Converts a bool to a i8. The resulting value is 0 for false and 1 for true values.

Examples
assert_eq!(i8::from(true), 1);
assert_eq!(i8::from(false), 0);

Converts NonZeroU8 to NonZeroUsize losslessly.

Convert to a Ready variant.

Example
assert_eq!(Poll::from(true), Poll::Ready(true));

Converts NonZeroU64 to NonZeroU128 losslessly.

Converts NonZeroI16 to NonZeroI32 losslessly.

Converts u8 to u64 losslessly.

Converts u8 to f64 losslessly.

Converts NonZeroU16 to NonZeroI64 losslessly.

Converts NonZeroI8 to NonZeroI128 losslessly.

Converts NonZeroI32 to NonZeroI64 losslessly.

Converts u16 to i128 losslessly.

Converts i16 to i128 losslessly.

Converts NonZeroU8 to NonZeroI128 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 NonZeroU32 to NonZeroI128 losslessly.

Converts NonZeroU32 to NonZeroI64 losslessly.

Converts NonZeroI32 to NonZeroI128 losslessly.

Converts i32 to i64 losslessly.

Converts i16 to i64 losslessly.

Converts NonZeroU8 to NonZeroU128 losslessly.

Converts NonZeroU16 to NonZeroU64 losslessly.

Converts NonZeroU16 to NonZeroU32 losslessly.

Converts u32 to f64 losslessly.

Converts u64 to u128 losslessly.

Converts NonZeroU8 to NonZeroI64 losslessly.

Converts NonZeroU16 to NonZeroUsize losslessly.

Converts u16 to usize losslessly.

Converts u8 to u16 losslessly.

Converts u8 to i64 losslessly.

Converts NonZeroI8 to NonZeroI16 losslessly.

Converts a bool to a u16. The resulting value is 0 for false and 1 for true values.

Examples
assert_eq!(u16::from(true), 1);
assert_eq!(u16::from(false), 0);

Converts NonZeroU8 to NonZeroU16 losslessly.

Converts i16 to i32 losslessly.

Converts a NonZeroI8 into an i8

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 u8 into a [char].

Examples
use std::mem;

let u = 32 as u8;
let c = char::from(u);
assert!(4 == mem::size_of_val(&c))

Move a boxed object to a new, reference counted, allocation.

Example
let original: Box<i32> = Box::new(1);
let shared: Rc<i32> = Rc::from(original);
assert_eq!(1, *shared);

Converts a T into an Arc<T>

The conversion moves the value into a newly allocated Arc. It is equivalent to calling Arc::new(t).

Example
let x = 5;
let arc = Arc::new(5);

assert_eq!(Arc::from(x), arc);

Create an atomically reference-counted pointer from a clone-on-write pointer by copying its content.

Example
let cow: Cow<str> = Cow::Borrowed("eggplant");
let shared: Arc<str> = Arc::from(cow);
assert_eq!("eggplant", &shared[..]);

Allocate a reference-counted slice and fill it by cloning v’s items.

Example
let original: &[i32] = &[1, 2, 3];
let shared: Arc<[i32]> = Arc::from(original);
assert_eq!(&[1, 2, 3], &shared[..]);

Allocate a reference-counted slice and fill it by cloning v’s items.

Example
let original: &[i32] = &[1, 2, 3];
let shared: Rc<[i32]> = Rc::from(original);
assert_eq!(&[1, 2, 3], &shared[..]);

Move a boxed object to a new, reference-counted allocation.

Example
let unique: Box<str> = Box::from("eggplant");
let shared: Arc<str> = Arc::from(unique);
assert_eq!("eggplant", &shared[..]);

Allocate a reference-counted str and copy v into it.

Example
let unique: String = "eggplant".to_owned();
let shared: Arc<str> = Arc::from(unique);
assert_eq!("eggplant", &shared[..]);

Allocate a reference-counted string slice and copy v into it.

Example
let original: String = "statue".to_owned();
let shared: Rc<str> = Rc::from(original);
assert_eq!("statue", &shared[..]);

Allocate a reference-counted str and copy v into it.

Example
let shared: Arc<str> = Arc::from("eggplant");
assert_eq!("eggplant", &shared[..]);

Allocate a reference-counted slice and move v’s items into it.

Example
let original: Box<Vec<i32>> = Box::new(vec![1, 2, 3]);
let shared: Rc<Vec<i32>> = Rc::from(original);
assert_eq!(vec![1, 2, 3], *shared);

Create a reference-counted pointer from a clone-on-write pointer by copying its content.

Example
let cow: Cow<str> = Cow::Borrowed("eggplant");
let shared: Rc<str> = Rc::from(cow);
assert_eq!("eggplant", &shared[..]);

Use a Wake-able type as a RawWaker.

No heap allocations or atomic operations are used for this conversion.

Use a Wake-able type as a Waker.

No heap allocations or atomic operations are used for this conversion.

Converts a generic type T into an Rc<T>

The conversion allocates on the heap and moves t from the stack into it.

Example
let x = 5;
let rc = Rc::new(5);

assert_eq!(Rc::from(x), rc);

Allocate a reference-counted string slice and copy v into it.

Example
let shared: Rc<str> = Rc::from("statue");
assert_eq!("statue", &shared[..]);

Converts a Box<T> into a Pin<Box<T>>

This conversion does not allocate on the heap and happens in place.

Allocate a reference-counted slice and move v’s items into it.

Example
let unique: Vec<i32> = vec![1, 2, 3];
let shared: Arc<[i32]> = Arc::from(unique);
assert_eq!(&[1, 2, 3], &shared[..]);

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

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.