Trait wasmtime_environ::__core::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

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

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

Converts a Cow into a box of dyn Error.

Examples
use std::error::Error;
use std::mem;
use std::borrow::Cow;

let a_cow_str_error = Cow::from("a str error");
let a_boxed_error = Box::<dyn Error>::from(a_cow_str_error);
assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))

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

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 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");

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

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);

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

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

Creates a clone-on-write pointer from an owned instance of PathBuf.

This conversion does not clone or allocate.

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

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

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

Converts a String into a box of dyn Error + Send + Sync.

Examples
use std::error::Error;
use std::mem;

let a_string_error = "a string error".to_string();
let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_string_error);
assert!(
    mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))

Converts a type of Error + Send + Sync into a box of dyn Error + Send + Sync.

Examples
use std::error::Error;
use std::fmt;
use std::mem;

#[derive(Debug)]
struct AnError;

impl fmt::Display for AnError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "An error")
    }
}

impl Error for AnError {}

unsafe impl Send for AnError {}

unsafe impl Sync for AnError {}

let an_error = AnError;
assert!(0 == mem::size_of_val(&an_error));
let a_boxed_error = Box::<dyn Error + Send + Sync>::from(an_error);
assert!(
    mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))

Converts a clone-on-write pointer to an owned path.

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

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

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)
)

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 String into an OsString.

This conversion does not allocate or copy memory.

Converts an OsString into a PathBuf

This conversion does not allocate or copy memory.

Creates a clone-on-write pointer from a reference to PathBuf.

This conversion does not clone or allocate.

Converts a PathBuf into a Box<Path>

This conversion currently should not allocate memory, but this behavior is not guaranteed on all platforms or in all future versions.

Converts a Cow into a box of dyn Error + Send + Sync.

Examples
use std::error::Error;
use std::mem;
use std::borrow::Cow;

let a_cow_str_error = Cow::from("a str error");
let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_cow_str_error);
assert!(
    mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))

Converts a String into a box of dyn Error.

Examples
use std::error::Error;
use std::mem;

let a_string_error = "a string error".to_string();
let a_boxed_error = Box::<dyn Error>::from(a_string_error);
assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))

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 NulError into a io::Error.

Converts a PathBuf into an OsString

This conversion does not allocate or copy memory.

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

Converts a String into a PathBuf

This conversion does not allocate or copy memory.

Converts a CStr into a borrowed Cow without copying or allocating.

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

Converts a type of Error into a box of dyn Error.

Examples
use std::error::Error;
use std::fmt;
use std::mem;

#[derive(Debug)]
struct AnError;

impl fmt::Display for AnError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "An error")
    }
}

impl Error for AnError {}

let an_error = AnError;
assert!(0 == mem::size_of_val(&an_error));
let a_boxed_error = Box::<dyn Error>::from(an_error);
assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))

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);

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

Converts a &CString into a borrowed Cow without copying or allocating.

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);

Converts a RecvError into a RecvTimeoutError.

This conversion always returns RecvTimeoutError::Disconnected.

No data is allocated on the heap.

Converts a str into a box of dyn Error + Send + Sync.

Examples
use std::error::Error;
use std::mem;

let a_str_error = "a str error";
let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_str_error);
assert!(
    mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))

Converts a SocketAddrV4 into a SocketAddr::V4.

Converts a SocketAddrV6 into a SocketAddr::V6.

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

Converts a CString into an owned Cow without copying or allocating.

Converts a Box<Path> into a PathBuf

This conversion does not allocate or copy memory.

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 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 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 borrowed OsStr to a PathBuf.

Allocates a PathBuf and copies the data into it.

Examples
use std::collections::HashMap;

let map1 = HashMap::from([(1, 2), (3, 4)]);
let map2: HashMap<_, _> = [(1, 2), (3, 4)].into();
assert_eq!(map1, map2);

Creates a clone-on-write pointer from a reference to Path.

This conversion does not clone or allocate.

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 a CString into a Vec<u8>.

The conversion consumes the CString, and removes the terminating NUL byte.

Examples
use std::collections::HashSet;

let set1 = HashSet::from([1, 2, 3, 4]);
let set2: HashSet<_> = [1, 2, 3, 4].into();
assert_eq!(set1, set2);

Creates a boxed Path from a reference.

This will allocate and clone path to it.

Creates a boxed Path from a clone-on-write pointer.

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

Converts a RecvError into a TryRecvError.

This conversion always returns TryRecvError::Disconnected.

No data is allocated on the heap.

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 str into a box of dyn Error.

Examples
use std::error::Error;
use std::mem;

let a_str_error = "a str error";
let a_boxed_error = Box::<dyn Error>::from(a_str_error);
assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))

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

Converts a NonZeroU64 into an u64

Converts u16 to f64 losslessly.

Converts u16 to u64 losslessly.

Converts u32 to u64 losslessly.

Converts i16 to i32 losslessly.

Converts a NonZeroIsize into an isize

Converts i16 to f64 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 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 a NonZeroUsize into an usize

Converts u8 to isize losslessly.

Converts a NonZeroI8 into an i8

Converts a NonZeroI16 into an i16

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 u8 to f32 losslessly.

Converts i8 to i128 losslessly.

Converts u8 to u32 losslessly.

Converts a NonZeroU32 into an u32

Converts a NonZeroI128 into an i128

Converts u16 to f32 losslessly.

Converts u8 to i128 losslessly.

Converts u64 to u128 losslessly.

Converts i8 to isize 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 u16 to u32 losslessly.

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 u32 to i128 losslessly.

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))

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 u8 to u64 losslessly.

Converts u8 to f64 losslessly.

Converts i32 to f64 losslessly.

Converts i8 to i32 losslessly.

Converts u16 to u128 losslessly.

Converts u16 to i64 losslessly.

Converts i32 to i64 losslessly.

Converts a NonZeroI64 into an i64

Converts i16 to isize losslessly.

Converts u32 to u128 losslessly.

Converts u16 to i32 losslessly.

Converts a NonZeroI32 into an i32

Converts i32 to i128 losslessly.

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 i16 to i128 losslessly.

Converts i8 to f32 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 u8 to u16 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 i8 to f64 losslessly.

Converts u8 to u128 losslessly.

Converts u16 to usize losslessly.

Converts a NonZeroU16 into an u16

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 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 u8 to usize losslessly.

Converts a NonZeroU8 into an u8

Converts u8 to i16 losslessly.

Converts u8 to i32 losslessly.

Converts u64 to i128 losslessly.

Converts i8 to i16 losslessly.

Converts a NonZeroU128 into an u128

Converts u8 to i64 losslessly.

Converts i8 to i64 losslessly.

Converts f32 to f64 losslessly.

Converts i64 to i128 losslessly.

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 u32 to f64 losslessly.

Converts u32 to i64 losslessly.

Converts u16 to i128 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 a char into a u64.

Examples
use std::mem;

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

Converts i16 to f32 losslessly.

Converts i16 to i64 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);
use std::collections::BTreeSet;

let set1 = BTreeSet::from([1, 2, 3, 4]);
let set2: BTreeSet<_> = [1, 2, 3, 4].into();
assert_eq!(set1, set2);

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[..]);

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[..]);

Converts a &String into a String.

This clones s and returns the clone.

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

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

Creates an Owned variant of Cow from an owned instance of Vec.

This conversion does not allocate or clone the data.

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

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

Turn a VecDeque<T> into a Vec<T>.

This never needs to re-allocate, but does need to do O(n) data movement if the circular buffer doesn’t happen to be at the beginning of the allocation.

Examples
use std::collections::VecDeque;

// This one is *O*(1).
let deque: VecDeque<_> = (1..5).collect();
let ptr = deque.as_slices().0.as_ptr();
let vec = Vec::from(deque);
assert_eq!(vec, [1, 2, 3, 4]);
assert_eq!(vec.as_ptr(), ptr);

// This one needs data rearranging.
let mut deque: VecDeque<_> = (1..5).collect();
deque.push_front(9);
deque.push_front(8);
let ptr = deque.as_slices().1.as_ptr();
let vec = Vec::from(deque);
assert_eq!(vec, [8, 9, 1, 2, 3, 4]);
assert_eq!(vec.as_ptr(), ptr);

Turn a Vec<T> into a VecDeque<T>.

This avoids reallocating where possible, but the conditions for that are strict, and subject to change, and so shouldn’t be relied upon unless the Vec<T> came from From<VecDeque<T>> and hasn’t been reallocated.

Converts a Cow<'_, [T]> into a Box<[T]>

When cow is the Cow::Borrowed variant, this conversion allocates on the heap and copies the underlying slice. Otherwise, it will try to reuse the owned Vec’s allocation.

Converts the given boxed str slice to a String. It is notable that the str slice is owned.

Examples

Basic usage:

let s1: String = String::from("hello world");
let s2: Box<str> = s1.into_boxed_str();
let s3: String = String::from(s2);

assert_eq!("hello world", s3)

Converts a string slice into a Borrowed variant. No heap allocation is performed, and the string is not copied.

Example
assert_eq!(Cow::from("eggplant"), Cow::Borrowed("eggplant"));

Convert a boxed slice into a vector by transferring ownership of the existing heap allocation.

Examples
let b: Box<[i32]> = vec![1, 2, 3].into_boxed_slice();
assert_eq!(Vec::from(b), vec![1, 2, 3]);

Always evaluates to TryReserveErrorKind::CapacityOverflow.

Converts a Vec<T> into a BinaryHeap<T>.

This conversion happens in-place, and has O(n) time complexity.

Converts a &[T] into a Box<[T]>

This conversion allocates on the heap and performs a copy of slice.

Examples
// create a &[u8] which will be used to create a Box<[u8]>
let slice: &[u8] = &[104, 101, 108, 108, 111];
let boxed_slice: Box<[u8]> = Box::from(slice);

println!("{:?}", boxed_slice);

Convert a vector into a boxed slice.

If v has excess capacity, its items will be moved into a newly-allocated buffer with exactly the right capacity.

Examples
assert_eq!(Box::from(vec![1, 2, 3]), vec![1, 2, 3].into_boxed_slice());

Allocates an owned String from a single character.

Example
let c: char = 'a';
let s: String = String::from(c);
assert_eq!("a", &s[..]);

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[..]);

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);

Converts a String into an Owned variant. No heap allocation is performed, and the string is not copied.

Example
let s = "eggplant".to_string();
let s2 = "eggplant".to_string();
assert_eq!(Cow::from(s), Cow::<'static, str>::Owned(s2));

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 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 Vec<T> and fill it by cloning s’s items.

Examples
assert_eq!(Vec::from(&[1, 2, 3][..]), vec![1, 2, 3]);

Converts a BinaryHeap<T> into a Vec<T>.

This conversion requires no data movement or allocation, and has constant time complexity.

use std::collections::LinkedList;

let list1 = LinkedList::from([1, 2, 3, 4]);
let list2: LinkedList<_> = [1, 2, 3, 4].into();
assert_eq!(list1, list2);

Converts a &str into a String.

The result is allocated on the heap.

Converts a String reference into a Borrowed variant. No heap allocation is performed, and the string is not copied.

Example
let s = "eggplant".to_string();
assert_eq!(Cow::from(&s), Cow::Borrowed("eggplant"));

Convert a clone-on-write slice into a vector.

If s already owns a Vec<T>, it will be returned directly. If s is borrowing a slice, a new Vec<T> will be allocated and filled by cloning s’s items into it.

Examples
let o: Cow<[i32]> = Cow::Owned(vec![1, 2, 3]);
let b: Cow<[i32]> = Cow::Borrowed(&[1, 2, 3]);
assert_eq!(Vec::from(o), Vec::from(b));
use std::collections::BTreeMap;

let map1 = BTreeMap::from([(1, 2), (3, 4)]);
let map2: BTreeMap<_, _> = [(1, 2), (3, 4)].into();
assert_eq!(map1, map2);

Converts a clone-on-write string to an owned instance of String.

This extracts the owned string, clones the string if it is not already owned.

Example
// If the string is not owned...
let cow: Cow<str> = Cow::Borrowed("eggplant");
// It will allocate on the heap and copy the string.
let owned: String = String::from(cow);
assert_eq!(&owned[..], "eggplant");

Converts a [T; N] into a Box<[T]>

This conversion moves the array to newly heap-allocated memory.

Examples
let boxed: Box<[u8]> = Box::from([4, 2]);
println!("{:?}", boxed);

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);

Converts the given String to a vector Vec that holds values of type u8.

Examples

Basic usage:

let s1 = String::from("hello world");
let v1 = Vec::from(s1);

for b in v1 {
    println!("{}", b);
}

Converts a Box<str> into a Box<[u8]>

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

Examples
// create a Box<str> which will be used to create a Box<[u8]>
let boxed: Box<str> = Box::from("hello");
let boxed_str: Box<[u8]> = Box::from(boxed);

// create a &[u8] which will be used to create a Box<[u8]>
let slice: &[u8] = &[104, 101, 108, 108, 111];
let boxed_slice = Box::from(slice);

assert_eq!(boxed_slice, boxed_str);

Converts a &mut str into a String.

The result is allocated on the heap.

use std::collections::VecDeque;

let deq1 = VecDeque::from([1, 2, 3, 4]);
let deq2: VecDeque<_> = [1, 2, 3, 4].into();
assert_eq!(deq1, deq2);

Creates a Borrowed variant of Cow from a slice.

This conversion does not allocate or clone the data.

use std::collections::BinaryHeap;

let mut h1 = BinaryHeap::from([1, 4, 2, 3]);
let mut h2: BinaryHeap<_> = [1, 4, 2, 3].into();
while let Some((a, b)) = h1.pop().zip(h2.pop()) {
    assert_eq!(a, b);
}

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 the given String to a boxed str slice that is owned.

Examples

Basic usage:

let s1: String = String::from("hello world");
let s2: Box<str> = Box::from(s1);
let s3: String = String::from(s2);

assert_eq!("hello world", s3)

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[..]);

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[..]);

Converts a Cow<'_, str> into a Box<str>

When cow is the Cow::Borrowed variant, this conversion allocates on the heap and copies the underlying str. Otherwise, it will try to reuse the owned String’s allocation.

Examples
use std::borrow::Cow;

let unboxed = Cow::Borrowed("hello");
let boxed: Box<str> = Box::from(unboxed);
println!("{}", boxed);
let unboxed = Cow::Owned("hello".to_string());
let boxed: Box<str> = Box::from(unboxed);
println!("{}", boxed);

Converts a T into a Box<T>

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

Examples
let x = 5;
let boxed = Box::new(5);

assert_eq!(Box::from(x), boxed);

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[..]);

Allocate a Vec<T> and fill it by cloning s’s items.

Examples
assert_eq!(Vec::from(&mut [1, 2, 3][..]), vec![1, 2, 3]);

Creates a Borrowed variant of Cow from a reference to Vec.

This conversion does not allocate or clone the data.

Allocate a Vec<u8> and fill it with a UTF-8 string.

Examples
assert_eq!(Vec::from("123"), vec![b'1', b'2', b'3']);

Converts a &str into a Box<str>

This conversion allocates on the heap and performs a copy of s.

Examples
let boxed: Box<str> = Box::from("hello");
println!("{}", boxed);

Implementors

[src]

impl From<__m128> for Simd<f32, 4_usize>

[src]

impl From<__m128d> for Simd<f64, 2_usize>

[src]

impl From<__m128i> for Simd<i8, 16_usize>

[src]

impl From<__m128i> for Simd<i16, 8_usize>

[src]

impl From<__m128i> for Simd<i32, 4_usize>

[src]

impl From<__m128i> for Simd<i64, 2_usize>

[src]

impl From<__m128i> for Simd<isize, 2_usize>

[src]

impl From<__m128i> for Simd<u8, 16_usize>

[src]

impl From<__m128i> for Simd<u16, 8_usize>

[src]

impl From<__m128i> for Simd<u32, 4_usize>

[src]

impl From<__m128i> for Simd<u64, 2_usize>

[src]

impl From<__m128i> for Simd<usize, 2_usize>

[src]

impl From<__m256> for Simd<f32, 8_usize>

[src]

impl From<__m256d> for Simd<f64, 4_usize>

[src]

impl From<__m256i> for Simd<i8, 32_usize>

[src]

impl From<__m256i> for Simd<i16, 16_usize>

[src]

impl From<__m256i> for Simd<i32, 8_usize>

[src]

impl From<__m256i> for Simd<i64, 4_usize>

[src]

impl From<__m256i> for Simd<isize, 4_usize>

[src]

impl From<__m256i> for Simd<u8, 32_usize>

[src]

impl From<__m256i> for Simd<u16, 16_usize>

[src]

impl From<__m256i> for Simd<u32, 8_usize>

[src]

impl From<__m256i> for Simd<u64, 4_usize>

[src]

impl From<__m256i> for Simd<usize, 4_usize>

[src]

impl From<__m512> for Simd<f32, 16_usize>

[src]

impl From<__m512d> for Simd<f64, 8_usize>

[src]

impl From<__m512i> for Simd<i8, 64_usize>

[src]

impl From<__m512i> for Simd<i16, 32_usize>

[src]

impl From<__m512i> for Simd<i32, 16_usize>

[src]

impl From<__m512i> for Simd<i64, 8_usize>

[src]

impl From<__m512i> for Simd<isize, 8_usize>

[src]

impl From<__m512i> for Simd<u8, 64_usize>

[src]

impl From<__m512i> for Simd<u16, 32_usize>

[src]

impl From<__m512i> for Simd<u32, 16_usize>

[src]

impl From<__m512i> for Simd<u64, 8_usize>

[src]

impl From<__m512i> for Simd<usize, 8_usize>

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.