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

Converts a NulError into a io::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 a Box<Path> into a PathBuf

This conversion does not allocate or copy memory.

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
);

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));

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 borrowed OsStr to a PathBuf.

Allocates a PathBuf and copies the data into it.

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 a PathBuf

This conversion does not allocate or copy memory.

Converts a SocketAddrV4 into a SocketAddr::V4.

Converts a PathBuf into an OsString

This conversion does not allocate or copy memory.

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"
);

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 tuple struct (Into<IpAddr>, u16) into a SocketAddr.

This conversion creates a SocketAddr::V4 for a IpAddr::V4 and creates a SocketAddr::V6 for a IpAddr::V6.

u16 is treated as port of the newly created SocketAddr.

Converts a String into a OsString.

This conversion does not allocate or copy memory.

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);

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

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 an OsString into a PathBuf

This conversion does not allocate or copy memory.

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

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));

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 clone-on-write pointer to an owned path.

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

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 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 a NonZeroU32 into an u32

Converts i16 to f64 losslessly.

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 NonZeroU32 to NonZeroU64 losslessly.

Converts NonZeroU8 to NonZeroI128 losslessly.

Converts a NonZeroU16 into an u16

Converts NonZeroU64 to NonZeroI128 losslessly.

Converts f32 to f64 losslessly.

Converts u16 to u64 losslessly.

Converts a NonZeroU128 into an u128

Converts i32 to f64 losslessly.

Converts u64 to i128 losslessly.

Converts u8 to u16 losslessly.

Converts u16 to u128 losslessly.

Converts i8 to f64 losslessly.

Converts from &Option<T> to Option<&T>.

Examples

Converts an Option<String> into an Option<usize>, preserving the original. The map method takes the self argument by value, consuming the original, so this technique uses as_ref to first take an Option to a reference to the value inside the original.

let s: Option<String> = Some(String::from("Hello, Rustaceans!"));
let o: Option<usize> = Option::from(&s).map(|ss: &String| ss.len());

println!("Can still print s: {:?}", s);

assert_eq!(o, Some(18));

Converts NonZeroU8 to NonZeroUsize losslessly.

Converts u8 to i64 losslessly.

Converts u32 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 u8 to i32 losslessly.

Converts u64 to u128 losslessly.

Converts i32 to i128 losslessly.

Converts u32 to i128 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 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 i16 to i64 losslessly.

Converts NonZeroU8 to NonZeroI32 losslessly.

Converts u16 to u32 losslessly.

Converts NonZeroU8 to NonZeroU16 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 i16 to i32 losslessly.

Converts i32 to i64 losslessly.

Converts u8 to u64 losslessly.

Converts NonZeroI16 to NonZeroI128 losslessly.

Converts a NonZeroU8 into an u8

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 NonZeroU16 to NonZeroI32 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 a NonZeroI64 into an i64

Converts NonZeroU8 to NonZeroU128 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 u16 to usize losslessly.

Converts a NonZeroI8 into an i8

Converts u8 to i16 losslessly.

Converts i8 to i32 losslessly.

Converts NonZeroI16 to NonZeroI32 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.

Copies val into a new Some.

Examples

let o: Option<u8> = Option::from(67);

assert_eq!(Some(67), o);

Converts NonZeroU64 to NonZeroU128 losslessly.

Converts from &mut Option<T> to Option<&mut T>

Examples

let mut s = Some(String::from("Hello"));
let o: Option<&mut String> = Option::from(&mut s);

match o {
    Some(t) => *t = String::from("Hello, Rustaceans!"),
    None => (),
}

assert_eq!(s, Some(String::from("Hello, Rustaceans!")));

Converts a NonZeroI16 into an i16

Converts u32 to i64 losslessly.

Converts NonZeroU32 to NonZeroU128 losslessly.

Converts NonZeroU16 to NonZeroU64 losslessly.

Converts NonZeroI16 to NonZeroIsize losslessly.

Converts NonZeroU8 to NonZeroU64 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 i8 to i16 losslessly.

Converts i8 to isize losslessly.

Converts i16 to i128 losslessly.

Converts a NonZeroUsize into an usize

Converts u8 to i128 losslessly.

Converts u16 to f32 losslessly.

Convert to a Ready variant.

Example

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

Converts a NonZeroI32 into an i32

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 u16 to f64 losslessly.

Converts u8 to f32 losslessly.

Converts i16 to isize losslessly.

Converts u8 to usize losslessly.

Converts a NonZeroIsize into an isize

Converts u16 to i64 losslessly.

Converts a NonZeroU64 into an u64

Converts NonZeroU8 to NonZeroU32 losslessly.

Converts a NonZeroI128 into an i128

Converts NonZeroU16 to NonZeroI64 losslessly.

Converts u8 to f64 losslessly.

Converts NonZeroU32 to NonZeroI128 losslessly.

Converts NonZeroI8 to NonZeroIsize losslessly.

Converts NonZeroI16 to NonZeroI64 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);

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 NonZeroI64 to NonZeroI128 losslessly.

Converts u8 to u32 losslessly.

Converts NonZeroU8 to NonZeroI16 losslessly.

Converts i8 to i128 losslessly.

Converts i16 to f32 losslessly.

Converts i8 to i64 losslessly.

Converts u16 to i32 losslessly.

Converts NonZeroI8 to NonZeroI128 losslessly.

Converts NonZeroU16 to NonZeroUsize losslessly.

Converts i64 to i128 losslessly.

Converts NonZeroU32 to NonZeroI64 losslessly.

Converts NonZeroI32 to NonZeroI64 losslessly.

Converts u32 to u64 losslessly.

Converts i8 to f32 losslessly.

Converts NonZeroU8 to NonZeroI64 losslessly.

Converts NonZeroU16 to NonZeroI128 losslessly.

Converts NonZeroI32 to NonZeroI128 losslessly.

Converts NonZeroI8 to NonZeroI32 losslessly.

Converts u8 to isize losslessly.

Converts NonZeroU8 to NonZeroIsize 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 NonZeroI8 to NonZeroI64 losslessly.

Converts NonZeroU16 to NonZeroU32 losslessly.

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 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 NonZeroU16 to NonZeroU128 losslessly.

Converts u8 to u128 losslessly.

Converts u16 to i128 losslessly.

Converts NonZeroI8 to NonZeroI16 losslessly.

Use a Wake-able type as a Waker.

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

Use a Wake-able type as a RawWaker.

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

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

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

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

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

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.

Implementors

Converts a bool into an AtomicBool.

Examples

use std::sync::atomic::AtomicBool;
let atomic_bool = AtomicBool::from(true);
assert_eq!(format!("{:?}", atomic_bool), "true")

Allocates an owned String from a single character.

Example

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

Converts an i8 into an AtomicI8.

Converts an i16 into an AtomicI16.

Converts an i32 into an AtomicI32.

Converts an i64 into an AtomicI64.

Converts an isize into an AtomicIsize.

Converts an u8 into an AtomicU8.

Converts an u16 into an AtomicU16.

Converts an u32 into an AtomicU32.

Converts an u64 into an AtomicU64.

Converts an usize into an AtomicUsize.

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 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)

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 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))

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 unique: String = "eggplant".to_owned();
let shared: Arc<str> = Arc::from(unique);
assert_eq!("eggplant", &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 RecvError into a RecvTimeoutError.

This conversion always returns RecvTimeoutError::Disconnected.

No data is allocated on the heap.

Converts a RecvError into a TryRecvError.

This conversion always returns TryRecvError::Disconnected.

No data is allocated on the heap.

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

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

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

Converts a CString into a Vec<u8>.

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

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

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

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

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

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

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);

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))

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 &str into a String.

The result is allocated on the heap.

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

Example

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

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 &String into a String.

This clones s and returns the clone.

Creates a boxed Path from a reference.

This will allocate and clone path to it.

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

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

Converts a &mut str into a String.

The result is allocated on the heap.

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

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

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);

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[..]);

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

Examples

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

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]);

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"));

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"));

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

This conversion does not clone or allocate.

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

This conversion does not clone or allocate.

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 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 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));

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

This conversion does not clone or allocate.

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 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))

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[..]);

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 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 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 a Borrowed variant of Cow from a reference to Vec.

This conversion does not allocate or clone the data.

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));

Creates a Borrowed variant of Cow from a slice.

This conversion does not allocate or clone the data.

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

This conversion does not allocate or clone the data.

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);

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.

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);

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[..]);

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.

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);

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[..]);

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

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

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);

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);

Converts a generic type T into a 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);

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

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

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]);

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());

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);

Convert an option into its packed equivalent.

Convert t into a packed Some(x).