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Trait std::convert::TryFrom ​

用于将T类型的值转化为Self类型的值，但是可能会出现转换失败的情况，它是 TryInto 的倒数。

rust
pub trait TryFrom<T>: Sized {
    type Error;

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

简单安全的类型转换在某些情况下可能会以受控方式失败。它是 TryInto 的倒数。

当您进行的类型转换可能会成功完成但可能还需要特殊处理时，这很有用。

例如，无法使用 From trait 将 i64 转换为 i32，因为 i64 可能包含 i32 无法表示的值，因此转换将丢失数据。

这可以通过将 i64 截断为 i32 (本质上给 i64 的值取 i32::MAX 模) 或通过简单地返回 i32::MAX 或其他方法来处理。

From trait 用于完美的转换，因此 TryFrom trait 会通知程序员类型转换何时会变差，并让他们决定如何处理它。

泛型实现 ​

  • TryFrom\<T> for U 意味着 TryInto\<U> for T
  • try_from 是反射的，这意味着 TryFrom\<T> for T 已实现并且不会失败 – 用于在类型 T 上调用 T::try_from() 的关联 Error 类型是 Infallible。 当 ! 类型稳定后，Infallible 和 ! 将等效。

TryFrom\<T> 可以实现如下：

rust
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))
        }
    }
}

如上所述，i32 实现了 TryFrom\<i64>：

rust
let big_number = 1_000_000_000_000i64;
// 默默地截断 `big_number`，事实之后需要检测并处理该截断。
let smaller_number = big_number as i32;
assert_eq!(smaller_number, -727379968);

// 由于 `big_number` 太大而无法容纳在 `i32` 中，因此返回错误。
let try_smaller_number = i32::try_from(big_number);
assert!(try_smaller_number.is_err());

// 返回 `Ok(3)`。
let try_successful_smaller_number = i32::try_from(3);
assert!(try_successful_smaller_number.is_ok());

Required Associated Types ​

Error ​

发生转换错误时返回的类型。

rust
type Error

Required Methods ​

try_from ​

转换函数，将T类型转化为Self类型并放入Ok中，若转换失败则返回Err

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

​

Implementors ​

impl TryFrom<char> for u8 ​

impl TryFrom<i8> for u8 ​

impl TryFrom<i8> for u16 ​

impl TryFrom<i8> for u32 ​

impl TryFrom<i8> for u64 ​

impl TryFrom<i8> for u128 ​

impl TryFrom<i8> for usize ​

impl TryFrom<i8> for NonZeroI8 ​

impl TryFrom<i16> for i8 ​

impl TryFrom<i16> for u8 ​

impl TryFrom<i16> for u16 ​

impl TryFrom<i16> for u32 ​

impl TryFrom<i16> for u64 ​

impl TryFrom<i16> for u128 ​

impl TryFrom<i16> for usize ​

impl TryFrom<i16> for NonZeroI16 ​

impl TryFrom<i32> for i8 ​

impl TryFrom<i32> for i16 ​

impl TryFrom<i32> for isize ​

impl TryFrom<i32> for u8 ​

impl TryFrom<i32> for u16 ​

impl TryFrom<i32> for u32 ​

impl TryFrom<i32> for u64 ​

impl TryFrom<i32> for u128 ​

impl TryFrom<i32> for usize ​

impl TryFrom<i32> for NonZeroI32 ​

impl TryFrom<i64> for i8 ​

impl TryFrom<i64> for i16 ​

impl TryFrom<i64> for i32 ​

impl TryFrom<i64> for isize ​

impl TryFrom<i64> for u8 ​

impl TryFrom<i64> for u16 ​

impl TryFrom<i64> for u32 ​

impl TryFrom<i64> for u64 ​

impl TryFrom<i64> for u128 ​

impl TryFrom<i64> for usize ​

impl TryFrom<i64> for NonZeroI64 ​

impl TryFrom<i128> for i8 ​

impl TryFrom<i128> for i16 ​

impl TryFrom<i128> for i32 ​

impl TryFrom<i128> for i64 ​

impl TryFrom<i128> for isize ​

impl TryFrom<i128> for u8 ​

impl TryFrom<i128> for u16 ​

impl TryFrom<i128> for u32 ​

impl TryFrom<i128> for u64 ​

impl TryFrom<i128> for u128 ​

impl TryFrom<i128> for usize ​

impl TryFrom<i128> for NonZeroI128 ​

impl TryFrom<isize> for i8 ​

impl TryFrom<isize> for i16 ​

impl TryFrom<isize> for i32 ​

impl TryFrom<isize> for i64 ​

impl TryFrom<isize> for i128 ​

impl TryFrom<isize> for u8 ​

impl TryFrom<isize> for u16 ​

impl TryFrom<isize> for u32 ​

impl TryFrom<isize> for u64 ​

impl TryFrom<isize> for u128 ​

impl TryFrom<isize> for usize ​

impl TryFrom<isize> for NonZeroIsize ​

impl TryFrom<u8> for i8 ​

impl TryFrom<u8> for NonZeroU8 ​

impl TryFrom<u16> for i8 ​

impl TryFrom<u16> for i16 ​

impl TryFrom<u16> for isize ​

impl TryFrom<u16> for u8 ​

impl TryFrom<u16> for NonZeroU16 ​

impl TryFrom<u32> for char ​

impl TryFrom<u32> for i8 ​

impl TryFrom<u32> for i16 ​

impl TryFrom<u32> for i32 ​

impl TryFrom<u32> for isize ​

impl TryFrom<u32> for u8 ​

impl TryFrom<u32> for u16 ​

impl TryFrom<u32> for usize ​

impl TryFrom<u32> for NonZeroU32 ​

impl TryFrom<u64> for i8 ​

impl TryFrom<u64> for i16 ​

impl TryFrom<u64> for i32 ​

impl TryFrom<u64> for i64 ​

impl TryFrom<u64> for isize ​

impl TryFrom<u64> for u8 ​

impl TryFrom<u64> for u16 ​

impl TryFrom<u64> for u32 ​

impl TryFrom<u64> for usize ​

impl TryFrom<u64> for NonZeroU64 ​

impl TryFrom<u128> for i8 ​

impl TryFrom<u128> for i16 ​

impl TryFrom<u128> for i32 ​

impl TryFrom<u128> for i64 ​

impl TryFrom<u128> for i128 ​

impl TryFrom<u128> for isize ​

impl TryFrom<u128> for u8 ​

impl TryFrom<u128> for u16 ​

impl TryFrom<u128> for u32 ​

impl TryFrom<u128> for u64 ​

impl TryFrom<u128> for usize ​

impl TryFrom<u128> for NonZeroU128 ​

impl TryFrom<usize> for i8 ​

impl TryFrom<usize> for i16 ​

impl TryFrom<usize> for i32 ​

impl TryFrom<usize> for i64 ​

impl TryFrom<usize> for i128 ​

impl TryFrom<usize> for isize ​

impl TryFrom<usize> for u8 ​

impl TryFrom<usize> for u16 ​

impl TryFrom<usize> for u32 ​

impl TryFrom<usize> for u64 ​

impl TryFrom<usize> for u128 ​

impl TryFrom<usize> for NonZeroUsize ​

impl TryFrom<usize> for Alignment ​

impl TryFrom<NonZeroI8> for NonZeroU8 ​

impl TryFrom<NonZeroI8> for NonZeroU16 ​

impl TryFrom<NonZeroI8> for NonZeroU32 ​

impl TryFrom<NonZeroI8> for NonZeroU64 ​

impl TryFrom<NonZeroI8> for NonZeroU128 ​

impl TryFrom<NonZeroI8> for NonZeroUsize ​

impl TryFrom<NonZeroI16> for NonZeroI8 ​

impl TryFrom<NonZeroI16> for NonZeroU8 ​

impl TryFrom<NonZeroI16> for NonZeroU16 ​

impl TryFrom<NonZeroI16> for NonZeroU32 ​

impl TryFrom<NonZeroI16> for NonZeroU64 ​

impl TryFrom<NonZeroI16> for NonZeroU128 ​

impl TryFrom<NonZeroI16> for NonZeroUsize ​

impl TryFrom<NonZeroI32> for NonZeroI8 ​

impl TryFrom<NonZeroI32> for NonZeroI16 ​

impl TryFrom<NonZeroI32> for NonZeroIsize ​

impl TryFrom<NonZeroI32> for NonZeroU8 ​

impl TryFrom<NonZeroI32> for NonZeroU16 ​

impl TryFrom<NonZeroI32> for NonZeroU32 ​

impl TryFrom<NonZeroI32> for NonZeroU64 ​

impl TryFrom<NonZeroI32> for NonZeroU128 ​

impl TryFrom<NonZeroI32> for NonZeroUsize ​

impl TryFrom<NonZeroI64> for NonZeroI8 ​

impl TryFrom<NonZeroI64> for NonZeroI16 ​

impl TryFrom<NonZeroI64> for NonZeroI32 ​

impl TryFrom<NonZeroI64> for NonZeroIsize ​

impl TryFrom<NonZeroI64> for NonZeroU8 ​

impl TryFrom<NonZeroI64> for NonZeroU16 ​

impl TryFrom<NonZeroI64> for NonZeroU32 ​

impl TryFrom<NonZeroI64> for NonZeroU64 ​

impl TryFrom<NonZeroI64> for NonZeroU128 ​

impl TryFrom<NonZeroI64> for NonZeroUsize ​

impl TryFrom<NonZeroI128> for NonZeroI8 ​

impl TryFrom<NonZeroI128> for NonZeroI16 ​

impl TryFrom<NonZeroI128> for NonZeroI32 ​

impl TryFrom<NonZeroI128> for NonZeroI64 ​

impl TryFrom<NonZeroI128> for NonZeroIsize ​

impl TryFrom<NonZeroI128> for NonZeroU8 ​

impl TryFrom<NonZeroI128> for NonZeroU16 ​

impl TryFrom<NonZeroI128> for NonZeroU32 ​

impl TryFrom<NonZeroI128> for NonZeroU64 ​

impl TryFrom<NonZeroI128> for NonZeroU128 ​

impl TryFrom<NonZeroI128> for NonZeroUsize ​

impl TryFrom<NonZeroIsize> for NonZeroI8 ​

impl TryFrom<NonZeroIsize> for NonZeroI16 ​

impl TryFrom<NonZeroIsize> for NonZeroI32 ​

impl TryFrom<NonZeroIsize> for NonZeroI64 ​

impl TryFrom<NonZeroIsize> for NonZeroI128 ​

impl TryFrom<NonZeroIsize> for NonZeroU8 ​

impl TryFrom<NonZeroIsize> for NonZeroU16 ​

impl TryFrom<NonZeroIsize> for NonZeroU32 ​

impl TryFrom<NonZeroIsize> for NonZeroU64 ​

impl TryFrom<NonZeroIsize> for NonZeroU128 ​

impl TryFrom<NonZeroIsize> for NonZeroUsize ​

impl TryFrom<NonZeroU8> for NonZeroI8 ​

impl TryFrom<NonZeroU16> for NonZeroI8 ​

impl TryFrom<NonZeroU16> for NonZeroI16 ​

impl TryFrom<NonZeroU16> for NonZeroIsize ​

impl TryFrom<NonZeroU16> for NonZeroU8 ​

impl TryFrom<NonZeroU32> for NonZeroI8 ​

impl TryFrom<NonZeroU32> for NonZeroI16 ​

impl TryFrom<NonZeroU32> for NonZeroI32 ​

impl TryFrom<NonZeroU32> for NonZeroIsize ​

impl TryFrom<NonZeroU32> for NonZeroU8 ​

impl TryFrom<NonZeroU32> for NonZeroU16 ​

impl TryFrom<NonZeroU32> for NonZeroUsize ​

impl TryFrom<NonZeroU64> for NonZeroI8 ​

impl TryFrom<NonZeroU64> for NonZeroI16 ​

impl TryFrom<NonZeroU64> for NonZeroI32 ​

impl TryFrom<NonZeroU64> for NonZeroI64 ​

impl TryFrom<NonZeroU64> for NonZeroIsize ​

impl TryFrom<NonZeroU64> for NonZeroU8 ​

impl TryFrom<NonZeroU64> for NonZeroU16 ​

impl TryFrom<NonZeroU64> for NonZeroU32 ​

impl TryFrom<NonZeroU64> for NonZeroUsize ​

impl TryFrom<NonZeroU128> for NonZeroI8 ​

impl TryFrom<NonZeroU128> for NonZeroI16 ​

impl TryFrom<NonZeroU128> for NonZeroI32 ​

impl TryFrom<NonZeroU128> for NonZeroI64 ​

impl TryFrom<NonZeroU128> for NonZeroI128 ​

impl TryFrom<NonZeroU128> for NonZeroIsize ​

impl TryFrom<NonZeroU128> for NonZeroU8 ​

impl TryFrom<NonZeroU128> for NonZeroU16 ​

impl TryFrom<NonZeroU128> for NonZeroU32 ​

impl TryFrom<NonZeroU128> for NonZeroU64 ​

impl TryFrom<NonZeroU128> for NonZeroUsize ​

impl TryFrom<NonZeroUsize> for NonZeroI8 ​

impl TryFrom<NonZeroUsize> for NonZeroI16 ​

impl TryFrom<NonZeroUsize> for NonZeroI32 ​

impl TryFrom<NonZeroUsize> for NonZeroI64 ​

impl TryFrom<NonZeroUsize> for NonZeroI128 ​

impl TryFrom<NonZeroUsize> for NonZeroIsize ​

impl TryFrom<NonZeroUsize> for NonZeroU8 ​

impl TryFrom<NonZeroUsize> for NonZeroU16 ​

impl TryFrom<NonZeroUsize> for NonZeroU32 ​

impl TryFrom<NonZeroUsize> for NonZeroU64 ​

impl TryFrom<NonZeroUsize> for NonZeroU128 ​

impl TryFrom<NonZeroUsize> for Alignment ​

impl TryFrom<HandleOrInvalid> for OwnedHandle

Available on Windows only.

impl TryFrom<HandleOrNull> for OwnedHandle

Available on Windows only.

impl<'a, T, const N: usize> TryFrom<&'a [T]> for &'a [T; N] ​

impl<'a, T, const N: usize> TryFrom<&'a mut [T]> for &'a mut [T; N] ​

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

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

impl<T, U> TryFrom<U> for T ​

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

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

rust
impl<T, const N: usize> TryFrom<&[T]> for [T; N]
where
  T: Copy,

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

rust
impl<T, const N: usize> TryFrom<&[T]> for Simd<T, N>
where
  LaneCount<N>: SupportedLaneCount,
  T: SimdElement,

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

rust
impl<T, const N: usize> TryFrom<&mut [T]> for [T; N]
where
  T: Copy,

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

rust
impl<T, const N: usize> TryFrom<&mut [T]> for Simd<T, N>
where
  LaneCount<N>: SupportedLaneCount,
  T: SimdElement,

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

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

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

impl<T, const N: usize> TryFrom<Vec<T, Global> ​

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