Trait tracing_core::stdlib::convert::TryFrom

1.34.0 · source ·
pub trait TryFrom<T>: Sized {
    type Error;

    // Required method
    fn try_from(value: T) -> Result<Self, Self::Error>;
}
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 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 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§

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type Error

The type returned in the event of a conversion error.

Required Methods§

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fn try_from(value: T) -> Result<Self, Self::Error>

Performs the conversion.

Object Safety§

This trait is not object safe.

Implementors§

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.

See impl From<u8> for char for details on the encoding.

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.

This corresponds to the UCS-2 encoding, as specified in ISO/IEC 10646:2003.

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impl TryFrom<i8> for u8

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impl TryFrom<i8> for u16

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impl TryFrom<i8> for u32

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impl TryFrom<i8> for u64

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impl TryFrom<i8> for u128

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impl TryFrom<i8> for usize

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impl TryFrom<i8> for NonZero<i8>

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impl TryFrom<i16> for i8

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impl TryFrom<i16> for u8

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impl TryFrom<i16> for u16

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impl TryFrom<i16> for u32

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impl TryFrom<i16> for u64

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impl TryFrom<i16> for u128

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impl TryFrom<i16> for usize

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impl TryFrom<i16> for NonZero<i16>

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impl TryFrom<i32> for i8

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impl TryFrom<i32> for i16

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impl TryFrom<i32> for isize

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impl TryFrom<i32> for u8

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impl TryFrom<i32> for u16

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impl TryFrom<i32> for u32

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impl TryFrom<i32> for u64

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impl TryFrom<i32> for u128

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impl TryFrom<i32> for usize

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impl TryFrom<i32> for NonZero<i32>

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impl TryFrom<i64> for i8

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impl TryFrom<i64> for i16

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impl TryFrom<i64> for i32

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impl TryFrom<i64> for isize

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impl TryFrom<i64> for u8

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impl TryFrom<i64> for u16

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impl TryFrom<i64> for u32

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impl TryFrom<i64> for u64

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impl TryFrom<i64> for u128

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impl TryFrom<i64> for usize

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impl TryFrom<i64> for NonZero<i64>

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impl TryFrom<i128> for i8

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impl TryFrom<i128> for i16

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impl TryFrom<i128> for i32

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impl TryFrom<i128> for i64

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impl TryFrom<i128> for isize

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impl TryFrom<i128> for u8

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impl TryFrom<i128> for u16

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impl TryFrom<i128> for u32

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impl TryFrom<i128> for u64

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impl TryFrom<i128> for u128

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impl TryFrom<i128> for usize

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impl TryFrom<i128> for NonZero<i128>

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impl TryFrom<isize> for i8

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impl TryFrom<isize> for i16

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impl TryFrom<isize> for i32

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impl TryFrom<isize> for i64

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impl TryFrom<isize> for i128

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impl TryFrom<isize> for u8

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impl TryFrom<isize> for u16

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impl TryFrom<isize> for u32

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impl TryFrom<isize> for u64

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impl TryFrom<isize> for u128

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impl TryFrom<isize> for usize

1.46.0 · source§

impl TryFrom<isize> for NonZero<isize>

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impl TryFrom<u8> for i8

1.46.0 · source§

impl TryFrom<u8> for NonZero<u8>

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impl TryFrom<u16> for i8

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impl TryFrom<u16> for i16

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impl TryFrom<u16> for isize

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impl TryFrom<u16> for u8

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impl TryFrom<u16> for NonZero<u16>

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impl TryFrom<u32> for char

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impl TryFrom<u32> for i8

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impl TryFrom<u32> for i16

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impl TryFrom<u32> for i32

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impl TryFrom<u32> for isize

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impl TryFrom<u32> for u8

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impl TryFrom<u32> for u16

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impl TryFrom<u32> for usize

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impl TryFrom<u32> for NonZero<u32>

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impl TryFrom<u64> for i8

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impl TryFrom<u64> for i16

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impl TryFrom<u64> for i32

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impl TryFrom<u64> for i64

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impl TryFrom<u64> for isize

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impl TryFrom<u64> for u8

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impl TryFrom<u64> for u16

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impl TryFrom<u64> for u32

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impl TryFrom<u64> for usize

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impl TryFrom<u64> for NonZero<u64>

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impl TryFrom<u128> for i8

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impl TryFrom<u128> for i16

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impl TryFrom<u128> for i32

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impl TryFrom<u128> for i64

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impl TryFrom<u128> for i128

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impl TryFrom<u128> for isize

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impl TryFrom<u128> for u8

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impl TryFrom<u128> for u16

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impl TryFrom<u128> for u32

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impl TryFrom<u128> for u64

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impl TryFrom<u128> for usize

1.46.0 · source§

impl TryFrom<u128> for NonZero<u128>

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impl TryFrom<usize> for i8

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impl TryFrom<usize> for i16

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impl TryFrom<usize> for i32

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impl TryFrom<usize> for i64

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impl TryFrom<usize> for i128

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impl TryFrom<usize> for isize

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impl TryFrom<usize> for u8

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impl TryFrom<usize> for u16

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impl TryFrom<usize> for u32

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impl TryFrom<usize> for u64

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impl TryFrom<usize> for u128

1.46.0 · source§

impl TryFrom<usize> for NonZero<usize>

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impl TryFrom<usize> for Alignment

1.49.0 · source§

impl TryFrom<NonZero<i8>> for NonZero<u8>

1.49.0 · source§

impl TryFrom<NonZero<i8>> for NonZero<u16>

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impl TryFrom<NonZero<i8>> for NonZero<u32>

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impl TryFrom<NonZero<i8>> for NonZero<u64>

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impl TryFrom<NonZero<i8>> for NonZero<u128>

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impl TryFrom<NonZero<i8>> for NonZero<usize>

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impl TryFrom<NonZero<i16>> for NonZero<i8>

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impl TryFrom<NonZero<i16>> for NonZero<u8>

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impl TryFrom<NonZero<i16>> for NonZero<u16>

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impl TryFrom<NonZero<i16>> for NonZero<u32>

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impl TryFrom<NonZero<i16>> for NonZero<u64>

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impl TryFrom<NonZero<i16>> for NonZero<u128>

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impl TryFrom<NonZero<i16>> for NonZero<usize>

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impl TryFrom<NonZero<i32>> for NonZero<i8>

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impl TryFrom<NonZero<i32>> for NonZero<i16>

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impl TryFrom<NonZero<i32>> for NonZero<isize>

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impl TryFrom<NonZero<i32>> for NonZero<u8>

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impl TryFrom<NonZero<i32>> for NonZero<u16>

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impl TryFrom<NonZero<i32>> for NonZero<u32>

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impl TryFrom<NonZero<i32>> for NonZero<u64>

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impl TryFrom<NonZero<i32>> for NonZero<u128>

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impl TryFrom<NonZero<i32>> for NonZero<usize>

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impl TryFrom<NonZero<i64>> for NonZero<i8>

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impl TryFrom<NonZero<i64>> for NonZero<i16>

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impl TryFrom<NonZero<i64>> for NonZero<i32>

1.49.0 · source§

impl TryFrom<NonZero<i64>> for NonZero<isize>

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impl TryFrom<NonZero<i64>> for NonZero<u8>

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impl TryFrom<NonZero<i64>> for NonZero<u16>

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impl TryFrom<NonZero<i64>> for NonZero<u32>

1.49.0 · source§

impl TryFrom<NonZero<i64>> for NonZero<u64>

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impl TryFrom<NonZero<i64>> for NonZero<u128>

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impl TryFrom<NonZero<i64>> for NonZero<usize>

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impl TryFrom<NonZero<i128>> for NonZero<i8>

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impl TryFrom<NonZero<i128>> for NonZero<i16>

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impl TryFrom<NonZero<i128>> for NonZero<i32>

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impl TryFrom<NonZero<i128>> for NonZero<i64>

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impl TryFrom<NonZero<i128>> for NonZero<isize>

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impl TryFrom<NonZero<i128>> for NonZero<u8>

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impl TryFrom<NonZero<i128>> for NonZero<u16>

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impl TryFrom<NonZero<i128>> for NonZero<u32>

1.49.0 · source§

impl TryFrom<NonZero<i128>> for NonZero<u64>

1.49.0 · source§

impl TryFrom<NonZero<i128>> for NonZero<u128>

1.49.0 · source§

impl TryFrom<NonZero<i128>> for NonZero<usize>

1.49.0 · source§

impl TryFrom<NonZero<isize>> for NonZero<i8>

1.49.0 · source§

impl TryFrom<NonZero<isize>> for NonZero<i16>

1.49.0 · source§

impl TryFrom<NonZero<isize>> for NonZero<i32>

1.49.0 · source§

impl TryFrom<NonZero<isize>> for NonZero<i64>

1.49.0 · source§

impl TryFrom<NonZero<isize>> for NonZero<i128>

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impl TryFrom<NonZero<isize>> for NonZero<u8>

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impl TryFrom<NonZero<isize>> for NonZero<u16>

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impl TryFrom<NonZero<isize>> for NonZero<u32>

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impl TryFrom<NonZero<isize>> for NonZero<u64>

1.49.0 · source§

impl TryFrom<NonZero<isize>> for NonZero<u128>

1.49.0 · source§

impl TryFrom<NonZero<isize>> for NonZero<usize>

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impl TryFrom<NonZero<u8>> for NonZero<i8>

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impl TryFrom<NonZero<u16>> for NonZero<i8>

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impl TryFrom<NonZero<u16>> for NonZero<i16>

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impl TryFrom<NonZero<u16>> for NonZero<isize>

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impl TryFrom<NonZero<u16>> for NonZero<u8>

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impl TryFrom<NonZero<u32>> for NonZero<i8>

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impl TryFrom<NonZero<u32>> for NonZero<i16>

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impl TryFrom<NonZero<u32>> for NonZero<i32>

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impl TryFrom<NonZero<u32>> for NonZero<isize>

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impl TryFrom<NonZero<u32>> for NonZero<u8>

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impl TryFrom<NonZero<u32>> for NonZero<u16>

1.49.0 · source§

impl TryFrom<NonZero<u32>> for NonZero<usize>

1.49.0 · source§

impl TryFrom<NonZero<u64>> for NonZero<i8>

1.49.0 · source§

impl TryFrom<NonZero<u64>> for NonZero<i16>

1.49.0 · source§

impl TryFrom<NonZero<u64>> for NonZero<i32>

1.49.0 · source§

impl TryFrom<NonZero<u64>> for NonZero<i64>

1.49.0 · source§

impl TryFrom<NonZero<u64>> for NonZero<isize>

1.49.0 · source§

impl TryFrom<NonZero<u64>> for NonZero<u8>

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impl TryFrom<NonZero<u64>> for NonZero<u16>

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impl TryFrom<NonZero<u64>> for NonZero<u32>

1.49.0 · source§

impl TryFrom<NonZero<u64>> for NonZero<usize>

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impl TryFrom<NonZero<u128>> for NonZero<i8>

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impl TryFrom<NonZero<u128>> for NonZero<i16>

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impl TryFrom<NonZero<u128>> for NonZero<i32>

1.49.0 · source§

impl TryFrom<NonZero<u128>> for NonZero<i64>

1.49.0 · source§

impl TryFrom<NonZero<u128>> for NonZero<i128>

1.49.0 · source§

impl TryFrom<NonZero<u128>> for NonZero<isize>

1.49.0 · source§

impl TryFrom<NonZero<u128>> for NonZero<u8>

1.49.0 · source§

impl TryFrom<NonZero<u128>> for NonZero<u16>

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impl TryFrom<NonZero<u128>> for NonZero<u32>

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impl TryFrom<NonZero<u128>> for NonZero<u64>

1.49.0 · source§

impl TryFrom<NonZero<u128>> for NonZero<usize>

1.49.0 · source§

impl TryFrom<NonZero<usize>> for NonZero<i8>

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impl TryFrom<NonZero<usize>> for NonZero<i16>

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impl TryFrom<NonZero<usize>> for NonZero<i32>

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impl TryFrom<NonZero<usize>> for NonZero<i64>

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impl TryFrom<NonZero<usize>> for NonZero<i128>

1.49.0 · source§

impl TryFrom<NonZero<usize>> for NonZero<isize>

1.49.0 · source§

impl TryFrom<NonZero<usize>> for NonZero<u8>

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impl TryFrom<NonZero<usize>> for NonZero<u16>

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impl TryFrom<NonZero<usize>> for NonZero<u32>

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impl TryFrom<NonZero<usize>> for NonZero<u64>

1.49.0 · source§

impl TryFrom<NonZero<usize>> for NonZero<u128>

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impl TryFrom<NonZero<usize>> for Alignment

1.72.0 · source§

impl<'a> TryFrom<&'a OsStr> for &'a str

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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));
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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));
1.43.0 · source§

impl<T, A, const N: usize> TryFrom<Arc<[T], A>> for Arc<[T; N], A>
where A: Allocator,

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type Error = Arc<[T], A>

1.48.0 · source§

impl<T, A, const N: usize> TryFrom<Vec<T, A>> for [T; N]
where A: Allocator,

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type Error = Vec<T, A>

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impl<T, U> TryFrom<U> for T
where U: Into<T>,

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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));
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impl<T, const N: usize> TryFrom<&[T]> for Simd<T, N>

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.

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));
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impl<T, const N: usize> TryFrom<&mut [T]> for Simd<T, N>

1.43.0 · source§

impl<T, const N: usize> TryFrom<Box<[T]>> for Box<[T; N]>

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type Error = Box<[T]>

1.43.0 · source§

impl<T, const N: usize> TryFrom<Rc<[T]>> for Rc<[T; N]>

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type Error = Rc<[T]>

1.66.0 · source§

impl<T, const N: usize> TryFrom<Vec<T>> for Box<[T; N]>

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type Error = Vec<T>