Trait std::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

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! 将等效。

TryFrom<T> 可以实现如下:

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))
        }
    }
}
Run

Examples

如上所述,i32 实现了 TryFrom<i64>

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());
Run

Required Associated Types§

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type Error

发生转换错误时返回的类型。

Required Methods§

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

执行转换。

Implementors§

1.59.0 · source§

impl TryFrom<char> for u8

将 U+0000..=U+00FF 中代码点的 char 映射到 0x00..=0xFF 中具有相同值的字节,如果代码点大于 U+00FF 则失败。

有关编码的详细信息,请参见 impl From<u8> for char

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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 NonZeroI8

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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 NonZeroI16

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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 NonZeroI32

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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 NonZeroI64

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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 NonZeroI128

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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

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impl TryFrom<isize> for NonZeroIsize

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impl TryFrom<u8> for i8

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impl TryFrom<u8> for NonZeroU8

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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 NonZeroU16

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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 NonZeroU32

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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 NonZeroU64

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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 NonZeroU128

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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 NonZeroUsize

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impl TryFrom<usize> for Alignment

1.49.0 · source§

impl TryFrom<NonZeroI8> for NonZeroU8

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impl TryFrom<NonZeroI8> for NonZeroU16

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impl TryFrom<NonZeroI8> for NonZeroU32

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impl TryFrom<NonZeroI8> for NonZeroU64

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impl TryFrom<NonZeroI8> for NonZeroU128

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impl TryFrom<NonZeroI8> for NonZeroUsize

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impl TryFrom<NonZeroI16> for NonZeroI8

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impl TryFrom<NonZeroI16> for NonZeroU8

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impl TryFrom<NonZeroI16> for NonZeroU16

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impl TryFrom<NonZeroI16> for NonZeroU32

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impl TryFrom<NonZeroI16> for NonZeroU64

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impl TryFrom<NonZeroI16> for NonZeroU128

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impl TryFrom<NonZeroI16> for NonZeroUsize

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impl TryFrom<NonZeroI32> for NonZeroI8

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impl TryFrom<NonZeroI32> for NonZeroI16

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impl TryFrom<NonZeroI32> for NonZeroIsize

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impl TryFrom<NonZeroI32> for NonZeroU8

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impl TryFrom<NonZeroI32> for NonZeroU16

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impl TryFrom<NonZeroI32> for NonZeroU32

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impl TryFrom<NonZeroI32> for NonZeroU64

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impl TryFrom<NonZeroI32> for NonZeroU128

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impl TryFrom<NonZeroI32> for NonZeroUsize

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impl TryFrom<NonZeroI64> for NonZeroI8

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impl TryFrom<NonZeroI64> for NonZeroI16

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impl TryFrom<NonZeroI64> for NonZeroI32

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impl TryFrom<NonZeroI64> for NonZeroIsize

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impl TryFrom<NonZeroI64> for NonZeroU8

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impl TryFrom<NonZeroI64> for NonZeroU16

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impl TryFrom<NonZeroI64> for NonZeroU32

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impl TryFrom<NonZeroI64> for NonZeroU64

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impl TryFrom<NonZeroI64> for NonZeroU128

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impl TryFrom<NonZeroI64> for NonZeroUsize

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impl TryFrom<NonZeroI128> for NonZeroI8

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impl TryFrom<NonZeroI128> for NonZeroI16

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impl TryFrom<NonZeroI128> for NonZeroI32

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impl TryFrom<NonZeroI128> for NonZeroI64

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impl TryFrom<NonZeroI128> for NonZeroIsize

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impl TryFrom<NonZeroI128> for NonZeroU8

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impl TryFrom<NonZeroI128> for NonZeroU16

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impl TryFrom<NonZeroI128> for NonZeroU32

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impl TryFrom<NonZeroI128> for NonZeroU64

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impl TryFrom<NonZeroI128> for NonZeroU128

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impl TryFrom<NonZeroI128> for NonZeroUsize

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impl TryFrom<NonZeroIsize> for NonZeroI8

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impl TryFrom<NonZeroIsize> for NonZeroI16

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impl TryFrom<NonZeroIsize> for NonZeroI32

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impl TryFrom<NonZeroIsize> for NonZeroI64

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impl TryFrom<NonZeroIsize> for NonZeroI128

1.49.0 · source§

impl TryFrom<NonZeroIsize> for NonZeroU8

1.49.0 · source§

impl TryFrom<NonZeroIsize> for NonZeroU16

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impl TryFrom<NonZeroIsize> for NonZeroU32

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impl TryFrom<NonZeroIsize> for NonZeroU64

1.49.0 · source§

impl TryFrom<NonZeroIsize> for NonZeroU128

1.49.0 · source§

impl TryFrom<NonZeroIsize> for NonZeroUsize

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impl TryFrom<NonZeroU8> for NonZeroI8

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impl TryFrom<NonZeroU16> for NonZeroI8

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impl TryFrom<NonZeroU16> for NonZeroI16

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impl TryFrom<NonZeroU16> for NonZeroIsize

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impl TryFrom<NonZeroU16> for NonZeroU8

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impl TryFrom<NonZeroU32> for NonZeroI8

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impl TryFrom<NonZeroU32> for NonZeroI16

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impl TryFrom<NonZeroU32> for NonZeroI32

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impl TryFrom<NonZeroU32> for NonZeroIsize

1.49.0 · source§

impl TryFrom<NonZeroU32> for NonZeroU8

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impl TryFrom<NonZeroU32> for NonZeroU16

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impl TryFrom<NonZeroU32> for NonZeroUsize

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impl TryFrom<NonZeroU64> for NonZeroI8

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impl TryFrom<NonZeroU64> for NonZeroI16

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impl TryFrom<NonZeroU64> for NonZeroI32

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impl TryFrom<NonZeroU64> for NonZeroI64

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impl TryFrom<NonZeroU64> for NonZeroIsize

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impl TryFrom<NonZeroU64> for NonZeroU8

1.49.0 · source§

impl TryFrom<NonZeroU64> for NonZeroU16

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impl TryFrom<NonZeroU64> for NonZeroU32

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impl TryFrom<NonZeroU64> for NonZeroUsize

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impl TryFrom<NonZeroU128> for NonZeroI8

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impl TryFrom<NonZeroU128> for NonZeroI16

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impl TryFrom<NonZeroU128> for NonZeroI32

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impl TryFrom<NonZeroU128> for NonZeroI64

1.49.0 · source§

impl TryFrom<NonZeroU128> for NonZeroI128

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impl TryFrom<NonZeroU128> for NonZeroIsize

1.49.0 · source§

impl TryFrom<NonZeroU128> for NonZeroU8

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impl TryFrom<NonZeroU128> for NonZeroU16

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impl TryFrom<NonZeroU128> for NonZeroU32

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impl TryFrom<NonZeroU128> for NonZeroU64

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impl TryFrom<NonZeroU128> for NonZeroUsize

1.49.0 · source§

impl TryFrom<NonZeroUsize> for NonZeroI8

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impl TryFrom<NonZeroUsize> for NonZeroI16

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impl TryFrom<NonZeroUsize> for NonZeroI32

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impl TryFrom<NonZeroUsize> for NonZeroI64

1.49.0 · source§

impl TryFrom<NonZeroUsize> for NonZeroI128

1.49.0 · source§

impl TryFrom<NonZeroUsize> for NonZeroIsize

1.49.0 · source§

impl TryFrom<NonZeroUsize> for NonZeroU8

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impl TryFrom<NonZeroUsize> for NonZeroU16

1.49.0 · source§

impl TryFrom<NonZeroUsize> for NonZeroU32

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impl TryFrom<NonZeroUsize> for NonZeroU64

1.49.0 · source§

impl TryFrom<NonZeroUsize> for NonZeroU128

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impl TryFrom<NonZeroUsize> for Alignment

1.63.0 · source§

impl TryFrom<HandleOrInvalid> for OwnedHandle

Available on Windows only.
1.63.0 · source§

impl TryFrom<HandleOrNull> for OwnedHandle

Available on Windows only.
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impl<'a, T, const N: usize> TryFrom<&'a [T]> for &'a [T; N]

尝试从切片 ref &[T] 创建数组 ref &[T; N]。 如果 slice.len() == N 则成功。

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]

尝试从一个非线性切片 ref &mut [T] 创建一个非线性数组 ref &mut [T; N]。 如果 slice.len() == N 则成功。

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));
Run
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 Twhere U: Into<T>,

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

尝试通过从切片 &[T] 复制来创建数组 [T; N]。 如果 slice.len() == N 则成功。

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>where LaneCount<N>: SupportedLaneCount, T: SimdElement,

1.59.0 · source§

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

尝试通过从无效切片 &mut [T] 复制来创建数组 [T; N]。 如果 slice.len() == N 则成功。

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

1.43.0 · source§

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

1.43.0 · source§

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

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type Error = Rc<[T]>

1.43.0 · source§

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

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type Error = Arc<[T]>

1.66.0 · source§

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

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type Error = Vec<T, Global>