Trait sp_std::convert::From

1.0.0 · source · [−]
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

Copies any value implementing AsRef<OsStr> into a newly allocated OsString.

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 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 NulError into a io::Error.

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
);

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 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<Path> into a PathBuf.

This conversion does not allocate or copy memory.

Converts a host byte order u32 into an Ipv4Addr.

Examples
use std::net::Ipv4Addr;

let addr = Ipv4Addr::from(0x12345678);
assert_eq!(Ipv4Addr::new(0x12, 0x34, 0x56, 0x78), addr);

Converts a Cow<'a, OsStr> into an OsString, by copying the contents if they are borrowed.

Converts a String into an OsString.

This conversion does not allocate or copy memory.

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));

Construct an exit code from an arbitrary u8 value.

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 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.

Copies the contents of the &CStr into a newly allocated CString.

Converts a PathBuf into an OsString

This conversion does not allocate or copy memory.

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(())
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);

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 String into a PathBuf

This conversion does not allocate or copy memory.

Converts a borrowed OsStr to a PathBuf.

Allocates a PathBuf and copies the data into it.

Converts a SocketAddrV6 into a SocketAddr::V6.

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);

Converts a SocketAddrV4 into a SocketAddr::V4.

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

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<CStr> into a CString 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);

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

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 creates 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 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 an Ipv4Addr into a host byte order u32.

Examples
use std::net::Ipv4Addr;

let addr = Ipv4Addr::new(0x12, 0x34, 0x56, 0x78);
assert_eq!(0x12345678, u32::from(addr));

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 clone-on-write pointer to an owned path.

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

Converts a Cow<'a, CStr> into a CString, by copying the contents if they are borrowed.

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

Converts i32 to i128 losslessly.

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

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

Converts u8 to i32 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 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 i16 to f64 losslessly.

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

Moves the value into a Poll::Ready to make a Poll<T>.

Example
assert_eq!(Poll::from(true), Poll::Ready(true));
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impl From<__m512i> for Simd<u32, 16_usize>

Converts i16 to f32 losslessly.

Converts a NonZeroUsize into an usize

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

Moves val into a new Some.

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

assert_eq!(Some(67), o);
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impl From<Simd<i8, 16_usize>> for __m128i

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

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

Converts a NonZeroU64 into an u64

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

Converts i16 to isize losslessly.

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

Converts u8 to u32 losslessly.

Converts u64 to i128 losslessly.

Converts u8 to f32 losslessly.

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

Converts u32 to u64 losslessly.

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

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

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

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

Creates a new OnceCell<T> which already contains the given value.

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

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

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

Converts i8 to isize losslessly.

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

Converts u16 to i64 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 a NonZeroI8 into an i8

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 from 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 a NonZeroU32 into an u32

Converts i8 to i32 losslessly.

Converts u8 to usize losslessly.

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

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

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

Converts u8 to i64 losslessly.

Converts u32 to u128 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))
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impl From<Simd<u64, 2_usize>> for __m128i

Converts u16 to u32 losslessly.

Converts u16 to u128 losslessly.

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

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

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

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

Converts u32 to i128 losslessly.

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

Converts i64 to i128 losslessly.

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

Converts u8 to i128 losslessly.

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

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

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

Converts u32 to i64 losslessly.

Converts u8 to f64 losslessly.

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

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

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 u16 to i32 losslessly.

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

Converts a NonZeroI16 into an i16

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

Converts u8 to i16 losslessly.

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

Converts a NonZeroI32 into an i32

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

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

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

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 a NonZeroU8 into an u8

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

Converts u16 to f64 losslessly.

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

Converts u8 to u128 losslessly.

Converts u16 to i128 losslessly.

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

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

Converts a NonZeroU16 into an u16

Converts i8 to f64 losslessly.

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

Converts u8 to u64 losslessly.

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

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

Converts i8 to i16 losslessly.

Converts a NonZeroI128 into an i128

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 i8 to i128 losslessly.

Converts u16 to f32 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);
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impl From<__m128> for Simd<f32, 4_usize>

Converts u32 to f64 losslessly.

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

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

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

Converts i8 to i64 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 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 a NonZeroI64 into an i64

Converts i16 to i32 losslessly.

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

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

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

Converts i32 to f64 losslessly.

Converts u8 to u16 losslessly.

Converts f32 to f64 losslessly.

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

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

Converts a NonZeroU128 into an u128

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!")));
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impl From<__m128i> for Simd<i64, 2_usize>

Converts i8 to f32 losslessly.

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

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

Converts u64 to u128 losslessly.

Converts u16 to usize losslessly.

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

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

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 NonZeroIsize into an isize

Converts u16 to u64 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);
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impl From<Simd<u32, 8_usize>> for __m256i

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

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

Converts i16 to i64 losslessly.

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

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

Converts u8 to isize losslessly.

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

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

Converts i16 to i128 losslessly.

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

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 i32 to i64 losslessly.

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

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

Converts a &String into a String.

This clones s and returns the clone.

Converts a &str into a String.

The result is allocated on the heap.

Always evaluates to TryReserveErrorKind::CapacityOverflow.

Converts a [T; N] into a LinkedList<T>.

use std::collections::LinkedList;

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

Use a Wake-able type as a Waker.

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.

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 &mut str into a String.

The result is allocated on the heap.

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");
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);
}

Allocates an owned String from a single character.

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

Use a Wake-able type as a RawWaker.

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

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.