Trait concordium_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. The From trait is intended for perfect conversions. If the conversion can fail or is not perfect, 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

Converts to this type from the input type.

Implementations on Foreign Types

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));

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 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 RecvError into a TryRecvError.

This conversion always returns TryRecvError::Disconnected.

No data is allocated on the heap.

Converts a SocketAddrV6 into a SocketAddr::V6.

Creates 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);

Construct an ExitCode from an arbitrary u8 value.

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 [alloc::ffi::NulError] into a io::Error.

Converts a SocketAddrV4 into a SocketAddr::V4.

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

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 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 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");

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

Converts a Box<Path> 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.

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

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 an OsString into a PathBuf

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));

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);

Moves the string into a Cow::Owned.

Converts a RecvError into a RecvTimeoutError.

This conversion always returns RecvTimeoutError::Disconnected.

No data is allocated on the heap.

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.

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");

Copies the string into a newly allocated Arc<OsStr>.

Converts a String into a PathBuf

This conversion does not allocate or copy memory.

Converts the string reference into a Cow::Borrowed.

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.

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 the string reference into a Cow::Borrowed.

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 OsString into an Arc<OsStr> by moving the OsString data into a new Arc buffer.

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

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

This conversion does not clone or allocate.

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 PathBuf into an OsString

This conversion does not allocate or copy memory.

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

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

This conversion does not clone or allocate.

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

This conversion does not clone or allocate.

Converts a String into an OsString.

This conversion does not allocate or copy memory.

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 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.

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
);

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 u16 to i64 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 a &T to a NonNull<T>.

This conversion is safe and infallible since references cannot be null.

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

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

Converts u8 to u64 losslessly.

Converts u64 to i128 losslessly.

Converts u32 to u128 losslessly.

Converts i16 to f64 losslessly.

Converts i8 to f32 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 NonZeroI32 into an i32

Converts an u32 into an AtomicU32.

Converts i16 to i128 losslessly.

Converts i32 to f64 losslessly.

Converts u8 to u32 losslessly.

Converts u8 to i32 losslessly.

Converts i16 to i64 losslessly.

Converts u64 to u128 losslessly.

Converts a NonZeroI8 into an i8

Converts u16 to u32 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 an isize into an AtomicIsize.

Converts an i16 into an AtomicI16.

Converts i8 to i32 losslessly.

Converts a NonZeroU128 into an u128

Converts i64 to i128 losslessly.

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

Converts u8 to usize 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 an u64 into an AtomicU64.

Converts a NonZeroI64 into an i64

Converts an usize into an AtomicUsize.

Moves val into a new Some.

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

assert_eq!(Some(67), o);

Converts a NonZeroI128 into an i128

Converts u8 to i128 losslessly.

Converts an u8 into an AtomicU8.

Converts a NonZeroI16 into an i16

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 i16 to isize losslessly.

Converts a NonZeroUsize into an usize

Converts i32 to i64 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 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 u32 to i64 losslessly.

Converts u32 to u64 losslessly.

Converts u16 to i32 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 i16 to i32 losslessly.

Converts an i64 into an AtomicI64.

Converts an i8 into an AtomicI8.

Converts i8 to i64 losslessly.

Converts an i32 into an AtomicI32.

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 NonZeroU8 into an u8

Converts i8 to i128 losslessly.

Converts u16 to u64 losslessly.

Converts i8 to i16 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 an u16 into an AtomicU16.

Converts u8 to i16 losslessly.

Converts i32 to i128 losslessly.

Converts u32 to f64 losslessly.

Converts u16 to usize losslessly.

Converts u16 to f32 losslessly.

Converts u16 to i128 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 u8 to f64 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 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 NonZeroIsize into an isize

Converts i8 to isize losslessly.

Converts a NonZeroU32 into an u32

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 u8 to f32 losslessly.

Converts i16 to f32 losslessly.

Converts u16 to f64 losslessly.

Converts i8 to f64 losslessly.

Converts u32 to i128 losslessly.

Converts u8 to isize losslessly.

Converts a NonZeroU64 into an u64

Converts a *mut T into an AtomicPtr<T>.

Converts a &mut T to a NonNull<T>.

This conversion is safe and infallible since references cannot be null.

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 u8 to i64 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 u16 to u128 losslessly.

Converts f32 to f64 losslessly.

Converts a NonZeroU16 into an u16

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 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 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 CString into an Arc<CStr> by moving the CString data into a new Arc buffer.

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

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

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

This conversion does not allocate or clone the data.

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

Converts a &CStr into a Arc<CStr>, by copying the contents into a newly allocated Arc.

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 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"));

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

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));

Use a Wake-able type as a RawWaker.

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

Creates a Borrowed variant of Cow from a slice.

This conversion does not allocate or clone the data.

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

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 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 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[..]);

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 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[..]);

Use a Wake-able type as a Waker.

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

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

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

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

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

This conversion does not allocate or clone the data.

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 an atomically reference-counted string slice into a byte slice.

Example
let string: Arc<str> = Arc::from("eggplant");
let bytes: Arc<[u8]> = Arc::from(string);
assert_eq!("eggplant".as_bytes(), bytes.as_ref());

Implementors

Full is mapped to i32::MIN + 3, Malformed is mapped to i32::MIN + 4.

MissingInitPrefix is mapped to i32::MIN + 5, TooLong to i32::MIN + 6, ContainsDot to i32::MIN + 9, and InvalidCharacters to i32::MIN + 10.

MissingDotSeparator is mapped to i32::MIN + 7, TooLong to i32::MIN + 8, and InvalidCharacters to i32::MIN + 11.

AmountTooLarge is i32::MIN + 13, MissingAccount is i32::MIN + 14.

Mapped to i32::MIN + 1.

The error code is i32::MIN + 12.

Mapped to i32::MIN + 2.

Convert the vector into a parameter as is.

AmountTooLarge is i32::MIN + 15, MissingAccount is i32::MIN + 16, MissingContract is i32::MIN + 17, MissingEntrypoint is i32::MIN + 18, MessageFailed is i32::MIN + 19, LogicReject is i32::MIN + 20, Trap is i32::MIN + 21.

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.