Simple and safe type conversions in to Self
. It is the reciprocal of
Into
.
This trait is useful when performing error handling as described by
the book and is closely related to the ?
operator.
When constructing a function that is capable of failing the return type
will generally be of the form Result<T, E>
.
The From
trait allows for simplification of error handling by providing a
means of returning a single error type that encapsulates numerous possible
erroneous situations.
This trait is not limited to error handling, rather the general case for
this trait would be in any type conversions to have an explicit definition
of how they are performed.
Note: this trait must not fail. If the conversion can fail, use
TryFrom
or a dedicated method which returns an Option<T>
or a
Result<T, E>
.
From<T> for U
implies Into<U>
for T
from
is reflexive, which means that From<T> for T
is implemented
String
implements From<&str>
:
let string = "hello".to_string();
let other_string = String::from("hello");
assert_eq!(string, other_string);Run
An example usage for error handling:
use std::io::{self, Read};
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 file = std::fs::File::open("test")?;
let mut contents = String::new();
file.read_to_string(&mut contents)?;
let num: i32 = contents.trim().parse()?;
Ok(num)
}Run
Converts a LocalWaker
into a Waker
.
This conversion turns a !Sync
LocalWaker
into a Sync
Waker
, allowing a wakeup
object to be sent to another thread, but giving up its ability to do specialized
thread-local wakeup behavior.
impl From<bool> for i8 | [src] |
Converts a bool
to a i8
. The resulting value is 0
for false
and 1
for true
values.
assert_eq!(i8::from(true), 1);
assert_eq!(i8::from(false), 0);Run
impl From<bool> for i16 | [src] |
Converts a bool
to a i16
. The resulting value is 0
for false
and 1
for true
values.
assert_eq!(i16::from(true), 1);
assert_eq!(i16::from(false), 0);Run
impl From<bool> for i32 | [src] |
Converts a bool
to a i32
. The resulting value is 0
for false
and 1
for true
values.
assert_eq!(i32::from(true), 1);
assert_eq!(i32::from(false), 0);Run
impl From<bool> for i64 | [src] |
Converts a bool
to a i64
. The resulting value is 0
for false
and 1
for true
values.
assert_eq!(i64::from(true), 1);
assert_eq!(i64::from(false), 0);Run
impl From<bool> for i128 | [src] |
Converts a bool
to a i128
. The resulting value is 0
for false
and 1
for true
values.
assert_eq!(i128::from(true), 1);
assert_eq!(i128::from(false), 0);Run
impl From<bool> for isize | [src] |
Converts a bool
to a isize
. The resulting value is 0
for false
and 1
for true
values.
assert_eq!(isize::from(true), 1);
assert_eq!(isize::from(false), 0);Run
impl From<bool> for u8 | [src] |
Converts a bool
to a u8
. The resulting value is 0
for false
and 1
for true
values.
assert_eq!(u8::from(true), 1);
assert_eq!(u8::from(false), 0);Run
impl From<bool> for u16 | [src] |
Converts a bool
to a u16
. The resulting value is 0
for false
and 1
for true
values.
assert_eq!(u16::from(true), 1);
assert_eq!(u16::from(false), 0);Run
impl From<bool> for u32 | [src] |
Converts a bool
to a u32
. The resulting value is 0
for false
and 1
for true
values.
assert_eq!(u32::from(true), 1);
assert_eq!(u32::from(false), 0);Run
impl From<bool> for u64 | [src] |
Converts a bool
to a u64
. The resulting value is 0
for false
and 1
for true
values.
assert_eq!(u64::from(true), 1);
assert_eq!(u64::from(false), 0);Run
impl From<bool> for u128 | [src] |
Converts a bool
to a u128
. The resulting value is 0
for false
and 1
for true
values.
assert_eq!(u128::from(true), 1);
assert_eq!(u128::from(false), 0);Run
impl From<bool> for usize | [src] |
Converts a bool
to a usize
. The resulting value is 0
for false
and 1
for true
values.
assert_eq!(usize::from(true), 1);
assert_eq!(usize::from(false), 0);Run
impl From<char> for u32 | [src] |
Converts a char
into a u32
.
use std::mem;
fn main() {
let c = 'c';
let u = u32::from(c);
assert!(4 == mem::size_of_val(&u))
}Run
impl From<f32> for f64 | [src] |
Converts f32
to f64
losslessly.
impl From<i8> for isize | [src] |
Converts i8
to isize
losslessly.
impl From<i16> for isize | [src] |
Converts i16
to isize
losslessly.
impl From<i16> for f32 | [src] |
Converts i16
to f32
losslessly.
impl From<i16> for f64 | [src] |
Converts i16
to f64
losslessly.
impl From<i16> for i32 | [src] |
Converts i16
to i32
losslessly.
impl From<i16> for i64 | [src] |
Converts i16
to i64
losslessly.
impl From<i16> for i128 | [src] |
Converts i16
to i128
losslessly.
impl From<i32> for f64 | [src] |
Converts i32
to f64
losslessly.
impl From<i32> for i64 | [src] |
Converts i32
to i64
losslessly.
impl From<i32> for i128 | [src] |
Converts i32
to i128
losslessly.
impl From<i64> for i128 | [src] |
Converts i64
to i128
losslessly.
impl From<i8> for f32 | [src] |
Converts i8
to f32
losslessly.
impl From<i8> for f64 | [src] |
Converts i8
to f64
losslessly.
impl From<i8> for i16 | [src] |
Converts i8
to i16
losslessly.
impl From<i8> for i32 | [src] |
Converts i8
to i32
losslessly.
impl From<i8> for i64 | [src] |
Converts i8
to i64
losslessly.
impl From<i8> for i128 | [src] |
Converts i8
to i128
losslessly.
impl From<u8> for usize | [src] |
Converts u8
to usize
losslessly.
impl From<u8> for isize | [src] |
Converts u8
to isize
losslessly.
impl From<u8> for char | [src] |
Maps a byte in 0x00...0xFF to a char
whose code point has the same value, in U+0000 to 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
.
use std::mem;
fn main() {
let u = 32 as u8;
let c = char::from(u);
assert!(4 == mem::size_of_val(&c))
}Run
impl From<u16> for usize | [src] |
Converts u16
to usize
losslessly.
impl From<u16> for f32 | [src] |
Converts u16
to f32
losslessly.
impl From<u16> for f64 | [src] |
Converts u16
to f64
losslessly.
impl From<u16> for i32 | [src] |
Converts u16
to i32
losslessly.
impl From<u16> for i64 | [src] |
Converts u16
to i64
losslessly.
impl From<u16> for i128 | [src] |
Converts u16
to i128
losslessly.
impl From<u16> for u32 | [src] |
Converts u16
to u32
losslessly.
impl From<u16> for u64 | [src] |
Converts u16
to u64
losslessly.
impl From<u16> for u128 | [src] |
Converts u16
to u128
losslessly.
impl From<u32> for f64 | [src] |
Converts u32
to f64
losslessly.
impl From<u32> for i64 | [src] |
Converts u32
to i64
losslessly.
impl From<u32> for i128 | [src] |
Converts u32
to i128
losslessly.
impl From<u32> for u64 | [src] |
Converts u32
to u64
losslessly.
impl From<u32> for u128 | [src] |
Converts u32
to u128
losslessly.
impl From<u64> for i128 | [src] |
Converts u64
to i128
losslessly.
impl From<u64> for u128 | [src] |
Converts u64
to u128
losslessly.
impl From<u8> for f32 | [src] |
Converts u8
to f32
losslessly.
impl From<u8> for f64 | [src] |
Converts u8
to f64
losslessly.
impl From<u8> for i16 | [src] |
Converts u8
to i16
losslessly.
impl From<u8> for i32 | [src] |
Converts u8
to i32
losslessly.
impl From<u8> for i64 | [src] |
Converts u8
to i64
losslessly.
impl From<u8> for i128 | [src] |
Converts u8
to i128
losslessly.
impl From<u8> for u16 | [src] |
Converts u8
to u16
losslessly.
impl From<u8> for u32 | [src] |
Converts u8
to u32
losslessly.
impl From<u8> for u64 | [src] |
Converts u8
to u64
losslessly.
impl From<u8> for u128 | [src] |
Converts u8
to u128
losslessly.
impl<T> From<T> for T | [src] |