Trait 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§

1.34.0 · Source

type Error

The type returned in the event of a conversion error.

Required Methods§

1.34.0 · Source

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

Performs the conversion.

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.

Trait TryFromCopy item path

§Generic Implementations

§Examples

Required Associated Types§

type Error

Required Methods§

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

Dyn Compatibility§

Implementors§

impl TryFrom<&SubstateKey> for AuthZoneField

type Error = ()

impl TryFrom<&SubstateKey> for BootLoaderField

type Error = ()

impl TryFrom<&SubstateKey> for ComponentField

type Error = ()

impl TryFrom<&SubstateKey> for FungibleBucketField

type Error = ()

impl TryFrom<&SubstateKey> for FungibleProofField

type Error = ()

impl TryFrom<&SubstateKey> for NonFungibleBucketField

type Error = ()

impl TryFrom<&SubstateKey> for NonFungibleProofField

type Error = ()

impl TryFrom<&SubstateKey> for ProtocolUpdateStatusField

type Error = ()

impl TryFrom<&SubstateKey> for RoyaltyField

type Error = ()

impl TryFrom<&SubstateKey> for TransactionTrackerField

type Error = ()

impl TryFrom<&SubstateKey> for TypeInfoField

type Error = ()

impl TryFrom<&SubstateKey> for WorktopField

type Error = ()

impl TryFrom<&str> for regex::regex::bytes::Regex

type Error = Error

impl TryFrom<&str> for regex::regex::string::Regex

type Error = Error

impl TryFrom<&str> for Decimal

type Error = ParseDecimalError

impl TryFrom<&str> for PreciseDecimal

type Error = ParsePreciseDecimalError

impl TryFrom<&str> for StringNonFungibleLocalId

type Error = ContentValidationError

impl TryFrom<&BigInt> for i8

type Error = TryFromBigIntError<()>

impl TryFrom<&BigInt> for i16

type Error = TryFromBigIntError<()>

impl TryFrom<&BigInt> for i32

type Error = TryFromBigIntError<()>

impl TryFrom<&BigInt> for i64

type Error = TryFromBigIntError<()>

impl TryFrom<&BigInt> for i128

type Error = TryFromBigIntError<()>

impl TryFrom<&BigInt> for isize

type Error = TryFromBigIntError<()>

impl TryFrom<&BigInt> for u8

type Error = TryFromBigIntError<()>

impl TryFrom<&BigInt> for u16

type Error = TryFromBigIntError<()>

impl TryFrom<&BigInt> for u32

type Error = TryFromBigIntError<()>

impl TryFrom<&BigInt> for u64

type Error = TryFromBigIntError<()>

impl TryFrom<&BigInt> for u128

type Error = TryFromBigIntError<()>

impl TryFrom<&BigInt> for usize

type Error = TryFromBigIntError<()>

impl TryFrom<&BigInt> for BigUint

type Error = TryFromBigIntError<()>

impl TryFrom<&BigUint> for i8

type Error = TryFromBigIntError<()>

impl TryFrom<&BigUint> for i16

type Error = TryFromBigIntError<()>

impl TryFrom<&BigUint> for i32

type Error = TryFromBigIntError<()>

impl TryFrom<&BigUint> for i64

type Error = TryFromBigIntError<()>

impl TryFrom<&BigUint> for i128

type Error = TryFromBigIntError<()>

impl TryFrom<&BigUint> for isize

Trait TryFrom