Trait sp_std::convert::From

1.0.0 · source ·

pub trait From<T>: Sized {
    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 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 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§

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fn from(value: T) -> Self

Converts to this type from the input type.

Implementors§

1.17.0 · source§

impl From<&str> for Box<str, Global>

1.6.0 · source§

impl From<&str> for Box<dyn Error + 'static, Global>

1.21.0 · source§

impl From<&str> for Rc<str>

1.21.0 · source§

impl From<&StreamResult> for Result<MZStatus, MZError>

1.35.0 · source§

impl From<&String> for String

1.17.0 · source§

impl From<&CStr> for Box<CStr, Global>

1.24.0 · source§

impl From<&CStr> for Rc<CStr>

1.24.0 · source§

impl From<&CStr> for Arc<CStr>

1.7.0 · source§

impl From<&CStr> for CString

1.17.0 · source§

impl From<&OsStr> for Box<OsStr, Global>

1.24.0 · source§

impl From<&OsStr> for Rc<OsStr>

1.24.0 · source§

impl From<&OsStr> for Arc<OsStr>

1.17.0 · source§

impl From<&Path> for Box<Path, Global>

1.24.0 · source§

impl From<&Path> for Rc<Path>

1.24.0 · source§

impl From<&Path> for Arc<Path>

1.44.0 · source§

impl From<&mut str> for String

1.45.0 · source§

impl From<Cow<'_, str>> for Box<str, Global>

1.45.0 · source§

impl From<Cow<'_, CStr>> for Box<CStr, Global>

1.45.0 · source§

impl From<Cow<'_, OsStr>> for Box<OsStr, Global>

1.45.0 · source§

impl From<Cow<'_, Path>> for Box<Path, Global>

1.34.0 (const: unstable) · source§

impl From<Infallible> for TryFromIntError

1.36.0 (const: unstable) · source§

impl From<Infallible> for TryFromSliceError

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impl From<TryReserveErrorKind> for TryReserveError

1.14.0 · source§

impl From<ErrorKind> for Error

Intended for use for errors not exposed to the user, where allocating onto the heap (for normal construction via Error::new) is too costly.

1.28.0 (const: unstable) · source§

impl From<bool> for i8

1.28.0 (const: unstable) · source§

impl From<bool> for i16

1.28.0 (const: unstable) · source§

impl From<bool> for i32

1.28.0 (const: unstable) · source§

impl From<bool> for i64

1.28.0 (const: unstable) · source§

impl From<bool> for i128

1.28.0 (const: unstable) · source§

impl From<bool> for isize

1.28.0 (const: unstable) · source§

impl From<bool> for u8

1.28.0 (const: unstable) · source§

impl From<bool> for u16

1.28.0 (const: unstable) · source§

impl From<bool> for u32

1.28.0 (const: unstable) · source§

impl From<bool> for u64

1.28.0 (const: unstable) · source§

impl From<bool> for u128

1.28.0 (const: unstable) · source§

impl From<bool> for usize

1.24.0 (const: unstable) · source§

impl From<bool> for AtomicBool

1.13.0 (const: unstable) · source§

impl From<char> for u32

1.51.0 (const: unstable) · source§

impl From<char> for u64

1.51.0 (const: unstable) · source§

impl From<char> for u128

1.46.0 · source§

impl From<char> for String

1.6.0 (const: unstable) · source§

impl From<f32> for f64

1.6.0 (const: unstable) · source§

impl From<i8> for f32

1.6.0 (const: unstable) · source§

impl From<i8> for f64

1.5.0 (const: unstable) · source§

impl From<i8> for i16

1.5.0 (const: unstable) · source§

impl From<i8> for i32

1.5.0 (const: unstable) · source§

impl From<i8> for i64

1.26.0 (const: unstable) · source§

impl From<i8> for i128

1.5.0 (const: unstable) · source§

impl From<i8> for isize

1.34.0 (const: unstable) · source§

impl From<i8> for AtomicI8

1.6.0 (const: unstable) · source§

impl From<i16> for f32

1.6.0 (const: unstable) · source§

impl From<i16> for f64

1.5.0 (const: unstable) · source§

impl From<i16> for i32

1.5.0 (const: unstable) · source§

impl From<i16> for i64

1.26.0 (const: unstable) · source§

impl From<i16> for i128

1.26.0 (const: unstable) · source§

impl From<i16> for isize

1.34.0 (const: unstable) · source§

impl From<i16> for AtomicI16

1.6.0 (const: unstable) · source§

impl From<i32> for f64

1.5.0 (const: unstable) · source§

impl From<i32> for i64

1.26.0 (const: unstable) · source§

impl From<i32> for i128

1.34.0 (const: unstable) · source§

impl From<i32> for AtomicI32

1.26.0 (const: unstable) · source§

impl From<i64> for i128

1.34.0 (const: unstable) · source§

impl From<i64> for AtomicI64

1.23.0 (const: unstable) · source§

impl From<isize> for AtomicIsize

1.34.0 (const: unstable) · source§

impl From<!> for Infallible

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impl From<!> for TryFromIntError

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.

1.6.0 (const: unstable) · source§