pub trait TryFrom<T>: Sized {
type Error;
// Required method
fn try_from(value: T) -> Result<Self, Self::Error> ⓘ;
}std only.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 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.
§Generic Implementations
TryFrom<T> for UimpliesTryInto<U> for Ttry_fromis reflexive, which means thatTryFrom<T> for Tis implemented and cannot fail – the associatedErrortype for callingT::try_from()on a value of typeTisInfallible. When the!type is stabilizedInfallibleand!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 values greater than zero!")
} else {
Ok(GreaterThanZero(value))
}
}
}§Examples
As described, i32 implements TryFrom<i64>:
let big_number = 1_000_000_000_000i64;
// Silently truncates `big_number`, requires detecting
// and handling the truncation after the fact.
let smaller_number = big_number as i32;
assert_eq!(smaller_number, -727379968);
// Returns an error because `big_number` is too big to
// fit in an `i32`.
let try_smaller_number = i32::try_from(big_number);
assert!(try_smaller_number.is_err());
// Returns `Ok(3)`.
let try_successful_smaller_number = i32::try_from(3);
assert!(try_successful_smaller_number.is_ok());Required Associated Types§
Required Methods§
Dyn Compatibility§
This trait is not dyn compatible.
In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.
Implementors§
Source§impl TryFrom<NotAvailable> for NotImplemented
impl TryFrom<NotAvailable> for NotImplemented
Source§impl TryFrom<NotAvailable> for NotSupported
impl TryFrom<NotAvailable> for NotSupported
Source§impl TryFrom<DataNotEnough> for NotEnoughElements
impl TryFrom<DataNotEnough> for NotEnoughElements
Source§impl TryFrom<DataNotEnough> for NotEnoughSpace
impl TryFrom<DataNotEnough> for NotEnoughSpace
Source§impl TryFrom<MismatchedBounds> for DataOverflow
impl TryFrom<MismatchedBounds> for DataOverflow
Source§impl TryFrom<MismatchedBounds> for IndexOutOfBounds
impl TryFrom<MismatchedBounds> for IndexOutOfBounds
Source§impl TryFrom<MismatchedBounds> for MismatchedCapacity
impl TryFrom<MismatchedBounds> for MismatchedCapacity
Source§impl TryFrom<MismatchedBounds> for MismatchedIndices
impl TryFrom<MismatchedBounds> for MismatchedIndices
Source§impl TryFrom<PartialSpace> for NotEnoughSpace
impl TryFrom<PartialSpace> for NotEnoughSpace
Source§impl TryFrom<PartialSpace> for PartiallyAdded
impl TryFrom<PartialSpace> for PartiallyAdded
Source§impl TryFrom<InvalidText> for MismatchedCapacity
impl TryFrom<InvalidText> for MismatchedCapacity
Source§impl TryFrom<InvalidText> for InvalidChar
impl TryFrom<InvalidText> for InvalidChar
Source§impl TryFrom<InvalidText> for InvalidUtf8
impl TryFrom<InvalidText> for InvalidUtf8
1.59.0 · Source§impl TryFrom<char> for u8
Maps a char with code point in U+0000..=U+00FF to a byte in 0x00..=0xFF with same value,
failing if the code point is greater than U+00FF.
impl TryFrom<char> for u8
Maps a char with code point in U+0000..=U+00FF to a 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.
type Error = TryFromCharError
1.74.0 · Source§impl TryFrom<char> for u16
Maps a char with code point in U+0000..=U+FFFF to a u16 in 0x0000..=0xFFFF with same value,
failing if the code point is greater than U+FFFF.
impl TryFrom<char> for u16
Maps a char with code point in U+0000..=U+FFFF to a u16 in 0x0000..=0xFFFF with same value,
failing if the code point is greater than U+FFFF.
This corresponds to the UCS-2 encoding, as specified in ISO/IEC 10646:2003.
type Error = TryFromCharError
Source§impl TryFrom<i8> for UnixTimeU32
impl TryFrom<i8> for UnixTimeU32
type Error = TryFromIntError
Source§impl TryFrom<i16> for UnixTimeU32
impl TryFrom<i16> for UnixTimeU32
type Error = TryFromIntError
Source§impl TryFrom<i32> for UnixTimeU32
impl TryFrom<i32> for UnixTimeU32
type Error = TryFromIntError
Source§impl TryFrom<i64> for UnixTimeU32
impl TryFrom<i64> for UnixTimeU32
type Error = TryFromIntError
Source§impl TryFrom<i128> for UnixTimeI64
impl TryFrom<i128> for UnixTimeI64
type Error = TryFromIntError
Source§impl TryFrom<i128> for UnixTimeU32
impl TryFrom<i128> for UnixTimeU32
type Error = TryFromIntError
Source§impl TryFrom<isize> for UnixTimeI64
impl TryFrom<isize> for UnixTimeI64
type Error = TryFromIntError
Source§impl TryFrom<isize> for UnixTimeU32
impl TryFrom<isize> for UnixTimeU32
type Error = TryFromIntError
Source§impl TryFrom<u64> for UnixTimeI64
impl TryFrom<u64> for UnixTimeI64
type Error = TryFromIntError
Source§impl TryFrom<u64> for UnixTimeU32
impl TryFrom<u64> for UnixTimeU32
type Error = TryFromIntError
Source§impl TryFrom<u128> for UnixTimeI64
impl TryFrom<u128> for UnixTimeI64
type Error = TryFromIntError
Source§impl TryFrom<u128> for UnixTimeU32
impl TryFrom<u128> for UnixTimeU32
type Error = TryFromIntError
Source§impl TryFrom<usize> for UnixTimeI64
impl TryFrom<usize> for UnixTimeI64
type Error = TryFromIntError
Source§impl TryFrom<usize> for UnixTimeU32
impl TryFrom<usize> for UnixTimeU32
type Error = TryFromIntError
§impl TryFrom<Duration> for Span
Converts a std::time::Duration to a Span.
impl TryFrom<Duration> for Span
Converts a std::time::Duration to a Span.
The span returned from this conversion will only ever have non-zero units of seconds or smaller.
§Errors
This only fails when the given Duration overflows the maximum number of
seconds representable by a Span.
§Example
This shows a basic conversion:
use std::time::Duration;
use jiff::{Span, ToSpan};
let duration = Duration::new(86_400, 123_456_789);
let span = Span::try_from(duration)?;
// A duration-to-span conversion always results in a span with
// non-zero units no bigger than seconds.
assert_eq!(
span,
86_400.seconds().milliseconds(123).microseconds(456).nanoseconds(789),
);
§Example: rounding
This example shows how to convert a Duration to a Span, and then round
it up to bigger units given a relative date:
use std::time::Duration;
use jiff::{civil::date, Span, SpanRound, ToSpan, Unit};
let duration = Duration::new(450 * 86_401, 0);
let span = Span::try_from(duration)?;
// We get back a simple span of just seconds:
assert_eq!(span, Span::new().seconds(450 * 86_401));
// But we can balance it up to bigger units:
let options = SpanRound::new()
.largest(Unit::Year)
.relative(date(2024, 1, 1));
assert_eq!(
span.round(options)?,
1.year().months(2).days(25).minutes(7).seconds(30),
);
Source§impl TryFrom<SystemTime> for UnixTimeI64
impl TryFrom<SystemTime> for UnixTimeI64
type Error = SystemTimeError
Source§impl TryFrom<UnixTimeI64> for UnixTimeU32
impl TryFrom<UnixTimeI64> for UnixTimeU32
type Error = TryFromIntError
§impl TryFrom<SignedDuration> for Span
Converts a SignedDuration to a Span.
impl TryFrom<SignedDuration> for Span
Converts a SignedDuration to a Span.
The span returned from this conversion will only ever have non-zero units of seconds or smaller.
§Errors
This only fails when the given SignedDuration overflows the maximum
number of seconds representable by a Span.
§Example
This shows a basic conversion:
use jiff::{SignedDuration, Span, ToSpan};
let duration = SignedDuration::new(86_400, 123_456_789);
let span = Span::try_from(duration)?;
// A duration-to-span conversion always results in a span with
// non-zero units no bigger than seconds.
assert_eq!(
span,
86_400.seconds().milliseconds(123).microseconds(456).nanoseconds(789),
);
§Example: rounding
This example shows how to convert a SignedDuration to a Span, and then
round it up to bigger units given a relative date:
use jiff::{civil::date, SignedDuration, Span, SpanRound, ToSpan, Unit};
let duration = SignedDuration::new(450 * 86_401, 0);
let span = Span::try_from(duration)?;
// We get back a simple span of just seconds:
assert_eq!(span, Span::new().seconds(450 * 86_401));
// But we can balance it up to bigger units:
let options = SpanRound::new()
.largest(Unit::Year)
.relative(date(2024, 1, 1));
assert_eq!(
span.round(options)?,
1.year().months(2).days(25).minutes(7).seconds(30),
);
§impl TryFrom<Span> for Duration
Converts a Span to a std::time::Duration.
impl TryFrom<Span> for Duration
Converts a Span to a std::time::Duration.
Note that this assumes that days are always 24 hours long.
§Errors
This can fail for only two reasons:
- The span is negative. This is an error because a
std::time::Durationis unsigned.) - The span has any non-zero units greater than days. This is an error because it’s impossible to determine the length of, e.g., a month without a reference date.
This can never result in overflow because a Duration can represent a
bigger span of time than Span when limited to units of days or lower.
If you need to convert a Span to a Duration that has non-zero units
bigger than days (or a Span with days of non-uniform length), then please
use Span::to_duration with a corresponding relative date.
§Example: maximal span
This example shows the maximum possible span using units of days or
smaller, and the corresponding Duration value:
use std::time::Duration;
use jiff::Span;
let sp = Span::new()
.days(7_304_484)
.hours(175_307_616)
.minutes(10_518_456_960i64)
.seconds(631_107_417_600i64)
.milliseconds(631_107_417_600_000i64)
.microseconds(631_107_417_600_000_000i64)
.nanoseconds(9_223_372_036_854_775_807i64);
let duration = Duration::try_from(sp)?;
assert_eq!(duration, Duration::new(3_795_867_877_636, 854_775_807));
§Example: converting a negative span
Since a Span is signed and a Duration is unsigned, converting
a negative Span to Duration will always fail. One can use
Span::signum to get the sign of the span and Span::abs to make the
span positive before converting it to a Duration:
use std::time::Duration;
use jiff::{Span, ToSpan};
let span = -86_400.seconds().nanoseconds(1);
let (sign, duration) = (span.signum(), Duration::try_from(span.abs())?);
assert_eq!((sign, duration), (-1, Duration::new(86_400, 1)));
§impl TryFrom<Span> for SignedDuration
Converts a Span to a SignedDuration.
impl TryFrom<Span> for SignedDuration
Converts a Span to a SignedDuration.
Note that this assumes that days are always 24 hours long.
§Errors
This can fail for only when the span has any non-zero units greater than days. This is an error because it’s impossible to determine the length of, e.g., a month without a reference date.
This can never result in overflow because a SignedDuration can represent
a bigger span of time than Span when limited to units of days or lower.
If you need to convert a Span to a SignedDuration that has non-zero
units bigger than days (or a Span with days of non-uniform length), then
please use Span::to_jiff_duration with a corresponding relative date.
§Example: maximal span
This example shows the maximum possible span using units of days or
smaller, and the corresponding SignedDuration value:
use jiff::{SignedDuration, Span};
let sp = Span::new()
.days(7_304_484)
.hours(175_307_616)
.minutes(10_518_456_960i64)
.seconds(631_107_417_600i64)
.milliseconds(631_107_417_600_000i64)
.microseconds(631_107_417_600_000_000i64)
.nanoseconds(9_223_372_036_854_775_807i64);
let duration = SignedDuration::try_from(sp)?;
assert_eq!(duration, SignedDuration::new(3_795_867_877_636, 854_775_807));
§impl<'a, 'py, T> TryFrom<BoundRef<'a, 'py, T>> for PyRef<'py, T>where
T: PyClass,
impl<'a, 'py, T> TryFrom<BoundRef<'a, 'py, T>> for PyRef<'py, T>where
T: PyClass,
type Error = PyBorrowError
§impl<'a, 'py, T> TryFrom<BoundRef<'a, 'py, T>> for PyRefMut<'py, T>where
T: PyClass<Frozen = False>,
impl<'a, 'py, T> TryFrom<BoundRef<'a, 'py, T>> for PyRefMut<'py, T>where
T: PyClass<Frozen = False>,
type Error = PyBorrowMutError
1.34.0 · Source§impl<'a, T, const N: usize> TryFrom<&'a [T]> for &'a [T; N]
Tries to create an array ref &[T; N] from a slice ref &[T]. Succeeds if
slice.len() == N.
impl<'a, T, const N: usize> TryFrom<&'a [T]> for &'a [T; N]
Tries to create an array ref &[T; N] from a slice ref &[T]. Succeeds if
slice.len() == N.
let bytes: [u8; 3] = [1, 0, 2];
let bytes_head: &[u8; 2] = <&[u8; 2]>::try_from(&bytes[0..2]).unwrap();
assert_eq!(1, u16::from_le_bytes(*bytes_head));
let bytes_tail: &[u8; 2] = bytes[1..3].try_into().unwrap();
assert_eq!(512, u16::from_le_bytes(*bytes_tail));type Error = TryFromSliceError
1.34.0 · Source§impl<'a, T, const N: usize> TryFrom<&'a mut [T]> for &'a mut [T; N]
Tries to create a mutable array ref &mut [T; N] from a mutable slice ref
&mut [T]. Succeeds if slice.len() == N.
impl<'a, T, const N: usize> TryFrom<&'a mut [T]> for &'a mut [T; N]
Tries to create a mutable array ref &mut [T; N] from a mutable slice ref
&mut [T]. Succeeds if slice.len() == N.
let mut bytes: [u8; 3] = [1, 0, 2];
let bytes_head: &mut [u8; 2] = <&mut [u8; 2]>::try_from(&mut bytes[0..2]).unwrap();
assert_eq!(1, u16::from_le_bytes(*bytes_head));
let bytes_tail: &mut [u8; 2] = (&mut bytes[1..3]).try_into().unwrap();
assert_eq!(512, u16::from_le_bytes(*bytes_tail));type Error = TryFromSliceError
§impl<'a, T, const N: usize> TryFrom<Box<'a, [T]>> for devela::_dep::bumpalo::boxed::Box<'a, [T; N]>
This impl replaces unsize coercion.
impl<'a, T, const N: usize> TryFrom<Box<'a, [T]>> for devela::_dep::bumpalo::boxed::Box<'a, [T; N]>
This impl replaces unsize coercion.
Source§impl<'a, const CAP: usize> TryFrom<&'a str> for ArrayString<CAP>
impl<'a, const CAP: usize> TryFrom<&'a str> for ArrayString<CAP>
type Error = CapacityError<&'a str>
Source§impl<'a, const CAP: usize> TryFrom<Arguments<'a>> for ArrayString<CAP>
impl<'a, const CAP: usize> TryFrom<Arguments<'a>> for ArrayString<CAP>
type Error = CapacityError<Error>
Source§impl<T> TryFrom<Interval<T>> for Range<T>
§Errors
Returns IncompatibleBounds if the bounds are not compatible.
impl<T> TryFrom<Interval<T>> for Range<T>
§Errors
Returns IncompatibleBounds if the bounds are not compatible.
Source§impl<T> TryFrom<Interval<T>> for RangeFrom<T>
§Errors
Returns IncompatibleBounds if the bounds are not compatible.
impl<T> TryFrom<Interval<T>> for RangeFrom<T>
§Errors
Returns IncompatibleBounds if the bounds are not compatible.
Source§impl<T> TryFrom<Interval<T>> for RangeFull
§Errors
Returns IncompatibleBounds if the bounds are not compatible.
impl<T> TryFrom<Interval<T>> for RangeFull
§Errors
Returns IncompatibleBounds if the bounds are not compatible.
Source§impl<T> TryFrom<Interval<T>> for RangeInclusive<T>
§Errors
Returns IncompatibleBounds if the bounds are not compatible.
impl<T> TryFrom<Interval<T>> for RangeInclusive<T>
§Errors
Returns IncompatibleBounds if the bounds are not compatible.
Source§impl<T> TryFrom<Interval<T>> for RangeTo<T>
§Errors
Returns IncompatibleBounds if the bounds are not compatible.
impl<T> TryFrom<Interval<T>> for RangeTo<T>
§Errors
Returns IncompatibleBounds if the bounds are not compatible.
Source§impl<T> TryFrom<Interval<T>> for RangeToInclusive<T>
§Errors
Returns IncompatibleBounds if the bounds are not compatible.
impl<T> TryFrom<Interval<T>> for RangeToInclusive<T>
§Errors
Returns IncompatibleBounds if the bounds are not compatible.
1.43.0 · Source§impl<T, A, const N: usize> TryFrom<Arc<[T], A>> for Arc<[T; N], A>where
A: Allocator,
impl<T, A, const N: usize> TryFrom<Arc<[T], A>> for Arc<[T; N], A>where
A: Allocator,
Source§impl<T, const CAP: usize> TryFrom<&[T]> for ArrayVec<T, CAP>where
T: Clone,
Try to create an ArrayVec from a slice. This will return an error if the slice was too big to
fit.
impl<T, const CAP: usize> TryFrom<&[T]> for ArrayVec<T, CAP>where
T: Clone,
Try to create an ArrayVec from a slice. This will return an error if the slice was too big to
fit.
use arrayvec::ArrayVec;
use std::convert::TryInto as _;
let array: ArrayVec<_, 4> = (&[1, 2, 3] as &[_]).try_into().unwrap();
assert_eq!(array.len(), 3);
assert_eq!(array.capacity(), 4);type Error = CapacityError
1.34.0 · Source§impl<T, const N: usize> TryFrom<&[T]> for [T; N]where
T: Copy,
Tries to create an array [T; N] by copying from a slice &[T].
Succeeds if slice.len() == N.
impl<T, const N: usize> TryFrom<&[T]> for [T; N]where
T: Copy,
Tries to create an array [T; N] by copying from a slice &[T].
Succeeds if slice.len() == N.
let bytes: [u8; 3] = [1, 0, 2];
let bytes_head: [u8; 2] = <[u8; 2]>::try_from(&bytes[0..2]).unwrap();
assert_eq!(1, u16::from_le_bytes(bytes_head));
let bytes_tail: [u8; 2] = bytes[1..3].try_into().unwrap();
assert_eq!(512, u16::from_le_bytes(bytes_tail));type Error = TryFromSliceError
1.59.0 · Source§impl<T, const N: usize> TryFrom<&mut [T]> for [T; N]where
T: Copy,
Tries to create an array [T; N] by copying from a mutable slice &mut [T].
Succeeds if slice.len() == N.
impl<T, const N: usize> TryFrom<&mut [T]> for [T; N]where
T: Copy,
Tries to create an array [T; N] by copying from a mutable slice &mut [T].
Succeeds if slice.len() == N.
let mut bytes: [u8; 3] = [1, 0, 2];
let bytes_head: [u8; 2] = <[u8; 2]>::try_from(&mut bytes[0..2]).unwrap();
assert_eq!(1, u16::from_le_bytes(bytes_head));
let bytes_tail: [u8; 2] = (&mut bytes[1..3]).try_into().unwrap();
assert_eq!(512, u16::from_le_bytes(bytes_tail));type Error = TryFromSliceError
Source§impl<T, const N: usize> TryFrom<&mut [T]> for Simd<T, N>
impl<T, const N: usize> TryFrom<&mut [T]> for Simd<T, N>
type Error = TryFromSliceError
Source§impl<const CAP: usize> TryFrom<&str> for StringNonul<CAP>
Available on crate feature _string_nonul only.
impl<const CAP: usize> TryFrom<&str> for StringNonul<CAP>
_string_nonul only.type Error = MismatchedCapacity
Source§impl<const CAP: usize> TryFrom<&str> for StringU16<CAP>
impl<const CAP: usize> TryFrom<&str> for StringU16<CAP>
type Error = MismatchedCapacity
Source§impl<const CAP: usize> TryFrom<&str> for StringU32<CAP>
impl<const CAP: usize> TryFrom<&str> for StringU32<CAP>
type Error = MismatchedCapacity
Source§impl<const CAP: usize> TryFrom<&str> for StringUsize<CAP>
impl<const CAP: usize> TryFrom<&str> for StringUsize<CAP>
type Error = MismatchedCapacity
Source§impl<const CAP: usize> TryFrom<&[u8]> for StringNonul<CAP>
Available on crate feature _string_nonul only.
impl<const CAP: usize> TryFrom<&[u8]> for StringNonul<CAP>
_string_nonul only.type Error = InvalidText
Source§impl<const CAP: usize> TryFrom<&[u8]> for StringUsize<CAP>
impl<const CAP: usize> TryFrom<&[u8]> for StringUsize<CAP>
type Error = InvalidText
Source§impl<const V: i8> TryFrom<i8> for devela::_info::examples::niche::NonValueI8<V>
Available on doc only.
impl<const V: i8> TryFrom<i8> for devela::_info::examples::niche::NonValueI8<V>
doc only.