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 和 ! 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§

source

type Error

发生转换错误时返回的类型。

Required Methods§

source

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。

§

Trait std::convert::TryFrom

泛型实现

Examples

Required Associated Types§

type Error

Required Methods§

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

Implementors§

impl TryFrom<char> for u8

type Error = TryFromCharError

impl TryFrom<i8> for u8

type Error = TryFromIntError

impl TryFrom<i8> for u16

type Error = TryFromIntError

impl TryFrom<i8> for u32

type Error = TryFromIntError

impl TryFrom<i8> for u64

type Error = TryFromIntError

impl TryFrom<i8> for u128

type Error = TryFromIntError

impl TryFrom<i8> for usize

type Error = TryFromIntError

impl TryFrom<i8> for NonZeroI8

type Error = TryFromIntError

impl TryFrom<i16> for i8

type Error = TryFromIntError

impl TryFrom<i16> for u8

type Error = TryFromIntError

impl TryFrom<i16> for u16

type Error = TryFromIntError

impl TryFrom<i16> for u32

type Error = TryFromIntError

impl TryFrom<i16> for u64

type Error = TryFromIntError

impl TryFrom<i16> for u128

type Error = TryFromIntError

impl TryFrom<i16> for usize

type Error = TryFromIntError

impl TryFrom<i16> for NonZeroI16

type Error = TryFromIntError

impl TryFrom<i32> for i8

type Error = TryFromIntError

impl TryFrom<i32> for i16

type Error = TryFromIntError

impl TryFrom<i32> for isize

type Error = TryFromIntError

impl TryFrom<i32> for u8

type Error = TryFromIntError

impl TryFrom<i32> for u16

type Error = TryFromIntError

impl TryFrom<i32> for u32

type Error = TryFromIntError

impl TryFrom<i32> for u64

type Error = TryFromIntError

impl TryFrom<i32> for u128

type Error = TryFromIntError

impl TryFrom<i32> for usize

type Error = TryFromIntError

impl TryFrom<i32> for NonZeroI32

type Error = TryFromIntError

impl TryFrom<i64> for i8

type Error = TryFromIntError

impl TryFrom<i64> for i16

type Error = TryFromIntError

impl TryFrom<i64> for i32

type Error = TryFromIntError

impl TryFrom<i64> for isize

type Error = TryFromIntError

impl TryFrom<i64> for u8

type Error = TryFromIntError

impl TryFrom<i64> for u16

type Error = TryFromIntError

impl TryFrom<i64> for u32

type Error = TryFromIntError

impl TryFrom<i64> for u64

type Error = TryFromIntError

impl TryFrom<i64> for u128

type Error = TryFromIntError

impl TryFrom<i64> for usize

type Error = TryFromIntError