Expand description
Simple and safe type conversions that may fail in a controlled
way under some circumstances. It is the reciprocal of TryInto
.
This is useful when you are doing a type conversion that may
trivially succeed but may also need special handling.
For example, there is no way to convert an i64
into an i32
using the From
trait, because an i64
may contain a value
that an i32
cannot represent and so the conversion would lose data.
This might be handled by truncating the i64
to an i32
(essentially
giving the i64
’s value modulo i32::MAX
) or by simply returning
i32::MAX
, or by some other method. The From
trait is intended
for perfect conversions, so the TryFrom
trait informs the
programmer when a type conversion could go bad and lets them
decide how to handle it.
TryFrom<T> for U
implies TryInto
<U> for T
try_from
is reflexive, which means that TryFrom<T> for T
is implemented and cannot fail – the associated Error
type for
calling T::try_from()
on a value of type T
is Infallible
.
When the !
type is stabilized Infallible
and !
will be
equivalent.
TryFrom<T>
can be implemented as follows:
struct GreaterThanZero(i32);
impl TryFrom<i32> for GreaterThanZero {
type Error = &'static str;
fn try_from(value: i32) -> Result<Self, Self::Error> {
if value <= 0 {
Err("GreaterThanZero only accepts value superior than zero!")
} else {
Ok(GreaterThanZero(value))
}
}
}
As described, i32
implements TryFrom<
i64
>
:
let big_number = 1_000_000_000_000i64;
let smaller_number = big_number as i32;
assert_eq!(smaller_number, -727379968);
let try_smaller_number = i32::try_from(big_number);
assert!(try_smaller_number.is_err());
let try_successful_smaller_number = i32::try_from(3);
assert!(try_successful_smaller_number.is_ok());
The type returned in the event of a conversion error.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Map char
with code point in U+0000..=U+00FF to byte in 0x00..=0xFF with same value, failing
if the code point is greater than U+00FF.
See impl From<u8> for char
for details on the encoding.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Try to create the target number type from a source
number type. This returns an error if the source value
is outside of the range of the target type.
Gets the entire contents of the Vec<T>
as an array,
if its size exactly matches that of the requested array.
assert_eq!(vec![1, 2, 3].try_into(), Ok([1, 2, 3]));
assert_eq!(<Vec<i32>>::new().try_into(), Ok([]));
If the length doesn’t match, the input comes back in Err
:
let r: Result<[i32; 4], _> = (0..10).collect::<Vec<_>>().try_into();
assert_eq!(r, Err(vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9]));
If you’re fine with just getting a prefix of the Vec<T>
,
you can call .truncate(N)
first.
let mut v = String::from("hello world").into_bytes();
v.sort();
v.truncate(2);
let [a, b]: [_; 2] = v.try_into().unwrap();
assert_eq!(a, b' ');
assert_eq!(b, b'd');
Attempts to convert a Box<[T]>
into a Box<[T; N]>
.
The conversion occurs in-place and does not require a
new memory allocation.
Returns the old Box<[T]>
in the Err
variant if
boxed_slice.len()
does not equal N
.