rama::crypto::dep::x509_parser::prelude::asn1_rs::nom::lib::std::convert

Trait From

pub trait From<T>: Sized {
    // Required method
    fn from(value: 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 From when specifying trait bounds on a generic function to ensure that types that only implement Into can be used as well.

The From trait 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>. From simplifies error handling by allowing a function to return a single error type that encapsulates 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 for T
From is reflexive, which means that From<T> for T is implemented

§When to implement `From`

While there’s no technical restrictions on which conversions can be done using a From implementation, the general expectation is that the conversions should typically be restricted as follows:

The conversion is infallible: if the conversion can fail, use TryFrom instead; don’t provide a From impl that panics.
The conversion is lossless: semantically, it should not lose or discard information. For example, i32: From<u16> exists, where the original value can be recovered using u16: TryFrom<i32>. And String: From<&str> exists, where you can get something equivalent to the original value via Deref. But From cannot be used to convert from u32 to u16, since that cannot succeed in a lossless way. (There’s some wiggle room here for information not considered semantically relevant. For example, Box<[T]>: From<Vec<T>> exists even though it might not preserve capacity, like how two vectors can be equal despite differing capacities.)
The conversion is value-preserving: the conceptual kind and meaning of the resulting value is the same, even though the Rust type and technical representation might be different. For example -1_i8 as u8 is lossless, since as casting back can recover the original value, but that conversion is not available via From because -1 and 255 are different conceptual values (despite being identical bit patterns technically). But f32: From<i16> is available because 1_i16 and 1.0_f32 are conceptually the same real number (despite having very different bit patterns technically). String: From<char> is available because they’re both text, but String: From<u32> is not available, since 1 (a number) and "1" (text) are too different. (Converting values to text is instead covered by the Display trait.)
The conversion is obvious: it’s the only reasonable conversion between the two types. Otherwise it’s better to have it be a named method or constructor, like how str::as_bytes is a method and how integers have methods like u32::from_ne_bytes, u32::from_le_bytes, and u32::from_be_bytes, none of which are From implementations. Whereas there’s only one reasonable way to wrap an Ipv6Addr into an IpAddr, thus IpAddr: From<Ipv6Addr> exists.

§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 with From::from.

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§

1.0.0 · Source

fn from(value: T) -> Self

Converts to this type from the input type.

Dyn Compatibility§

§Examples

use icu::locale::{
    langid,
    subtags::{language, region, script},
};

let lid = langid!("en-Latn-US");
let (lang, script, region) = (&lid).into();

assert_eq!(lang, language!("en"));
assert_eq!(script, Some(script!("Latn")));
assert_eq!(region, Some(region!("US")));

§

impl From<(Language, Option<Script>, Option<Region>)> for LanguageIdentifier

Convert from an LSR tuple to a [LanguageIdentifier].

§Examples

use icu::locale::{
    langid,
    subtags::{language, region, script},
    LanguageIdentifier,
};

let lang = language!("en");
let script = script!("Latn");
let region = region!("US");
assert_eq!(
    LanguageIdentifier::from((lang, Some(script), Some(region))),
    langid!("en-Latn-US")
);

§

impl From<(Language, Option<Script>, Option<Region>)> for Locale

§Examples

use icu::locale::Locale;
use icu::locale::{
    locale,
    subtags::{language, region, script},
};

assert_eq!(
    Locale::from((
        language!("en"),
        Some(script!("Latn")),
        Some(region!("US"))
    )),
    locale!("en-Latn-US")
);

use icu::locale::{langid, subtags::region, LanguageIdentifier};

assert_eq!(
    LanguageIdentifier::from(Some(region!("US"))),
    langid!("und-US")
);

§

impl From<Option<Region>> for Locale

§Examples

use icu::locale::Locale;
use icu::locale::{locale, subtags::region};

assert_eq!(Locale::from(Some(region!("US"))), locale!("und-US"));

§

impl From<Option<Script>> for LanguageIdentifier

§Examples

use icu::locale::{langid, subtags::script, LanguageIdentifier};

assert_eq!(
    LanguageIdentifier::from(Some(script!("latn"))),
    langid!("und-Latn")
);

§

impl From<Option<Script>> for Locale

§Examples

use icu::locale::Locale;
use icu::locale::{locale, subtags::script};

assert_eq!(Locale::from(Some(script!("latn"))), locale!("und-Latn"));

§

impl From<u8> for CertificateType

Source §

impl From<u8> for serde_json::value::Value

1.13.0 (const: unstable) · Source§

impl From<u8> for char

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.

impl From<Version> for HttpVersion

§

impl From<Authority> for Uri

Convert an Authority into a Uri.

§

impl From<InvalidUri> for rama::http::HttpError

§

impl From<InvalidUriParts> for rama::http::HttpError

§

impl From<PathAndQuery> for Uri

use icu::locale::{langid, subtags::language, LanguageIdentifier};

assert_eq!(LanguageIdentifier::from(language!("en")), langid!("en"));

§

impl From<Language> for Locale

§Examples

use icu::locale::Locale;
use icu::locale::{locale, subtags::language};

assert_eq!(Locale::from(language!("en")), locale!("en"));

impl<'a> From<Oid<'a>> for BerObject<'a>

Build a DER object from an OID.

impl<'data> From<&'data mut [MaybeUninit<u8>]> for BorrowedBuf<'data>

Creates a new BorrowedBuf from an uninitialized buffer.

Use set_init if part of the buffer is known to be already initialized.

Source §

impl<'data> From<BorrowedCursor<'data>> for BorrowedBuf<'data>

Creates a new BorrowedBuf from a cursor.

Use BorrowedCursor::with_unfilled_buf instead for a safer alternative.

On Windows, a corresponding From<&impl AsSocket> implementation exists.

impl<L, R> From<Either<L, R>> for Result<R, L>

Convert from Either to Result with Right => Ok and Left => Err.

This trait is implemented for tuples up to twelve items long.

1.34.0 (const: unstable) · Source§

impl<T> From<!> for T

impl<T> From<(T₁, T₂, …, Tₙ)> for [T; N]

This trait is implemented for tuples up to twelve items long.

§

impl<const N: usize> From<[Method; N]> for AllowMethods

§

Trait FromCopy item path

§Generic Implementations

§When to implement From

§Examples

Required Methods§

fn from(value: T) -> Self

Dyn Compatibility§

Implementors§

impl From<&'static str> for rama::telemetry::opentelemetry::Value

impl From<&'static str> for AnyValue

impl From<&'static str> for TraceError

impl From<&'static str> for Bytes

impl From<&'static str> for Body

impl From<&'static str> for rama::telemetry::opentelemetry::Key

impl From<&'static str> for StringValue

impl From<&'static str> for ProtoError

impl From<&'static str> for ResolveError

impl From<&'static Tls12CipherSuite> for SupportedCipherSuite

impl From<&'static Tls13CipherSuite> for SupportedCipherSuite

impl From<&'static [u8]> for Bytes

impl From<&'static [u8]> for Body

impl From<&ApplicationProtocol> for rama::crypto::dep::x509_parser::prelude::asn1_rs::nom::lib::std::vec::Vec<u8>

impl From<&SocketAddr> for Interface

impl From<&SocketAddr> for Authority

impl From<&SocketAddr> for SocketAddress

impl From<&SocketAddr> for NodeId

impl From<&str> for serde_json::value::Value

impl From<&str> for Utf8Bytes

impl From<&str> for HeapReader

impl From<&str> for StringFilter

impl From<&str> for BaggageMetadata

impl From<&str> for rama::crypto::dep::x509_parser::prelude::asn1_rs::nom::lib::std::boxed::Box<str>

impl From<&str> for String

impl From<&str> for rama::crypto::dep::x509_parser::prelude::asn1_rs::nom::lib::std::vec::Vec<u8>

impl From<&str> for Rc<str>

impl From<&str> for Arc<str>

impl From<&str> for SmolStr

impl From<&str> for Value

impl From<&str> for Vec<u8>

impl From<&PerMessageDeflateConfig> for rama::http::ws::protocol::PerMessageDeflateConfig

impl From<&Method> for AllowMethods

impl From<&Scheme> for rama::net::Protocol

impl From<&PerMessageDeflateConfig> for rama::http::headers::sec_websocket_extensions::PerMessageDeflateConfig

impl From<&SocketAddress> for Interface

impl From<&SocketAddress> for Authority

impl From<&SocketAddress> for SockAddr

impl From<&RequestContext> for TransportContext

impl From<&TransportContext> for ProxyContext

impl From<&StringFilter> for String

impl From<&Parts> for TransportContext

impl From<&Request> for TransportContext

impl From<&UserAgentProfile> for SelectedUserAgentProfile

impl From<&PublicKey> for PublicKeyComponents<Vec<u8>>

impl From<&Box<dyn Error + Sync + Send>> for ReplyKind

impl From<&Formatter<'_>> for FormatterOptions

impl From<&String> for Utf8Bytes

impl From<&String> for StringFilter

impl From<&String> for String

impl From<&String> for SmolStr

impl From<&CStr> for rama::crypto::dep::x509_parser::prelude::asn1_rs::nom::lib::std::boxed::Box<CStr>

impl From<&CStr> for CString

impl From<&CStr> for Rc<CStr>

impl From<&CStr> for Arc<CStr>

impl From<&OsStr> for rama::crypto::dep::x509_parser::prelude::asn1_rs::nom::lib::std::boxed::Box<OsStr>

impl From<&OsStr> for Rc<OsStr>

impl From<&OsStr> for Arc<OsStr>

impl From<&Path> for rama::crypto::dep::x509_parser::prelude::asn1_rs::nom::lib::std::boxed::Box<Path>

impl From<&Path> for Rc<Path>

impl From<&Path> for Arc<Path>

impl From<&BorrowedFormatItem<'_>> for OwnedFormatItem

impl From<&ChaCha8Rng> for ChaCha8Rng

impl From<&ChaCha12Rng> for ChaCha12Rng

impl From<&ChaCha20Rng> for ChaCha20Rng

impl From<&LanguageIdentifier> for (Language, Option<Script>, Option<Region>)

§Examples

impl From<&LanguageIdentifier> for DataLocale

impl From<&LanguageIdentifier> for LocalePreferences

impl From<&Locale> for DataLocale

impl From<&Locale> for LocalePreferences

impl From<&ScopedIp> for core::net::ip_addr::IpAddr

Trait From

§When to implement `From`