Trait sp_std::convert::TryFrom

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

    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 (essentially giving the i64’s value modulo i32::MAX) 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§

The type returned in the event of a conversion error.

Required Methods§

Performs the conversion.

Implementors§

Map char with code point in U+0000..=U+00FF to 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.

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));

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));

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));

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));

impl<T, const CAP: usize> TryFrom<&[T]> for ArrayVec<T, CAP>where
    T: Clone,

impl<'a, const CAP: usize> TryFrom<&'a str> for ArrayString<CAP>

impl<'a, const CAP: usize> TryFrom<Arguments<'a>> for ArrayString<CAP>

impl<T: AsRawFd + From<OwnedFd>> TryFrom<OwnedFd> for Async<T>

impl<T: Into<OwnedFd>> TryFrom<Async<T>> for OwnedFd

impl<'a> TryFrom<&'a [u8]> for Public

impl<'a> TryFrom<&'a [u8]> for Signature

impl<A, O> TryFrom<&BitSlice<<A as BitView>::Store, O>> for BitArray<A, O>where
    A: BitViewSized,
    O: BitOrder,

impl<A, O> TryFrom<&BitSlice<<A as BitView>::Store, O>> for &BitArray<A, O>where
    A: BitViewSized,
    O: BitOrder,

impl<A, O> TryFrom<&mut BitSlice<<A as BitView>::Store, O>> for &mut BitArray<A, O>where
    A: BitViewSized,
    O: BitOrder,

impl<T, O> TryFrom<Box<[T], Global>> for BitBox<T, O>where
    T: BitStore,
    O: BitOrder,

impl<T, O> TryFrom<*const T> for BitPtr<Const, T, O>where
    T: BitStore,
    O: BitOrder,

impl<T, O> TryFrom<*mut T> for BitPtr<Mut, T, O>where
    T: BitStore,
    O: BitOrder,

impl<'a, T, O> TryFrom<&'a [T]> for &'a BitSlice<T, O>where
    T: BitStore,
    O: BitOrder,

impl<'a, T, O> TryFrom<&'a mut [T]> for &'a mut BitSlice<T, O>where
    T: BitStore,
    O: BitOrder,

impl<T, O> TryFrom<Vec<T, Global>> for BitVec<T, O>where
    T: BitStore,
    O: BitOrder,

impl<T, const L: usize, const U: usize> TryFrom<Vec<T, Global>> for BoundedVec<T, L, U>

impl<const S: usize> TryFrom<String> for Cid<S>

impl<const S: usize> TryFrom<&str> for Cid<S>

impl<const S: usize> TryFrom<Vec<u8, Global>> for Cid<S>

impl<const S: usize> TryFrom<&[u8]> for Cid<S>

impl TryFrom<u64> for Version

impl TryFrom<u16> for Opcode

impl<'a> TryFrom<&'a [u8]> for Any<'a>

impl<'a> TryFrom<Any<'a>> for BitString<'a>

impl<'a> TryFrom<&'a [u8]> for BitString<'a>

impl<'a> TryFrom<&&'a [u8]> for BitString<'a>

impl<'a> TryFrom<BitString<'a>> for &'a [u8]

impl TryFrom<Any<'_>> for bool

impl<'a, T> TryFrom<Any<'a>> for ContextSpecific<T>where
    T: Decodable<'a>,

impl<'a> TryFrom<Any<'a>> for Ia5String<'a>

impl<'a> TryFrom<Any<'a>> for UIntBytes<'a>

impl TryFrom<Any<'_>> for i8

impl TryFrom<Any<'_>> for i16

impl TryFrom<Any<'_>> for i32

impl TryFrom<Any<'_>> for i64

impl TryFrom<Any<'_>> for i128

impl TryFrom<Any<'_>> for u8

impl TryFrom<Any<'_>> for u16

impl TryFrom<Any<'_>> for u32

impl TryFrom<Any<'_>> for u64

impl TryFrom<Any<'_>> for u128

impl TryFrom<Any<'_>> for Null

impl TryFrom<Any<'_>> for ()

impl<'a> TryFrom<Any<'a>> for OctetString<'a>

impl<'a> TryFrom<Any<'a>> for PrintableString<'a>

impl TryFrom<Any<'_>> for UtcTime

impl<'a> TryFrom<Any<'a>> for Utf8String<'a>

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

impl TryFrom<u32> for Length

impl TryFrom<usize> for Length

impl TryFrom<Length> for usize

impl TryFrom<u8> for TagNumber

impl TryFrom<u8> for Tag

impl<C> TryFrom<&[u8]> for Signature<C>where
    C: PrimeCurve,
    MaxSize<C>: ArrayLength<u8>,
    <FieldSize<C> as Add>::Output: Add<MaxOverhead> + ArrayLength<u8>,

impl<C> TryFrom<Signature<C>> for Signature<C>where
    C: PrimeCurve,
    MaxSize<C>: ArrayLength<u8>,
    <FieldSize<C> as Add>::Output: Add<MaxOverhead> + ArrayLength<u8>,

impl<C> TryFrom<&[u8]> for SigningKey<C>where
    C: PrimeCurve + ProjectiveArithmetic,
    Scalar<C>: Invert<Output = Scalar<C>> + Reduce<C::UInt> + SignPrimitive<C>,
    SignatureSize<C>: ArrayLength<u8>,

impl<C> TryFrom<&[u8]> for VerifyingKey<C>where
    C: PrimeCurve + ProjectiveArithmetic,
    AffinePoint<C>: FromEncodedPoint<C> + ToEncodedPoint<C>,
    FieldSize<C>: ModulusSize,

impl<C> TryFrom<&[u8]> for Signature<C>where
    C: PrimeCurve,
    SignatureSize<C>: ArrayLength<u8>,

impl TryFrom<&[u8]> for Signature

impl TryFrom<&[u8]> for Signature

impl TryFrom<&[u8]> for SigningKey

impl<C> TryFrom<&[u8]> for NonZeroScalar<C>where
    C: Curve + ScalarArithmetic,

impl<C> TryFrom<EcPrivateKey<'_>> for SecretKey<C>where
    C: Curve + ValidatePublicKey,
    FieldSize<C>: ModulusSize,

impl<T> TryFrom<u8> for BitFlags<T>where
    T: BitFlag<Numeric = u8>,

impl<T> TryFrom<u16> for BitFlags<T>where
    T: BitFlag<Numeric = u16>,

impl<T> TryFrom<u32> for BitFlags<T>where
    T: BitFlag<Numeric = u32>,

impl<T> TryFrom<u64> for BitFlags<T>where
    T: BitFlag<Numeric = u64>,

impl<T> TryFrom<u128> for BitFlags<T>where
    T: BitFlag<Numeric = u128>,

impl<'a, K, V, T> TryFrom<&'a HashMap<K, V, RandomState>> for HeaderMap<T>where
    K: Eq + Hash,
    HeaderName: TryFrom<&'a K>,
    <HeaderName as TryFrom<&'a K>>::Error: Into<Error>,
    T: TryFrom<&'a V>,
    T::Error: Into<Error>,

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

impl<'a> TryFrom<&'a String> for HeaderName

impl<'a> TryFrom<&'a [u8]> for HeaderName

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

impl<'a> TryFrom<&'a String> for HeaderValue

impl<'a> TryFrom<&'a [u8]> for HeaderValue

impl<'a> TryFrom<&'a [u8]> for Method

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

impl<'a> TryFrom<&'a [u8]> for StatusCode

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

impl<'a> TryFrom<&'a [u8]> for Authority

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

impl<'a> TryFrom<&'a [u8]> for PathAndQuery

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

impl<'a> TryFrom<Vec<u8, Global>> for PathAndQuery

impl<'a> TryFrom<&'a [u8]> for Scheme

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

impl<'a> TryFrom<&'a [u8]> for Uri

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

impl<'a> TryFrom<&'a String> for Uri

impl TryFrom<String> for Uri

impl<'a> TryFrom<Vec<u8, Global>> for Uri

impl TryFrom<Parts> for Uri

impl<'a> TryFrom<&'a Uri> for Uri

impl TryFrom<&[u8]> for ReasonPhrase

impl TryFrom<BigInt> for i64

impl TryFrom<BigInt> for u64

impl TryFrom<BigInt> for i128

impl TryFrom<BigInt> for u128

impl TryFrom<Uri> for Target

impl<'a> TryFrom<Value> for SubscriptionId<'a>

impl TryFrom<&[u8]> for Signature

impl TryFrom<u8> for Id

impl TryFrom<Vec<u8, Global>> for PeerId

impl TryFrom<Multihash<64>> for PeerId

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

impl TryFrom<u64> for Code

impl TryFrom<Error> for Errno

impl TryFrom<i32> for Signal

impl TryFrom<U128> for u8

impl TryFrom<U128> for u16

impl TryFrom<U128> for u32

impl TryFrom<U128> for usize

impl TryFrom<U128> for u64

impl TryFrom<U128> for i8

impl TryFrom<U128> for i16

impl TryFrom<U128> for i32

impl TryFrom<U128> for isize

impl TryFrom<U128> for i64

impl TryFrom<U128> for u128

impl TryFrom<U128> for i128

impl TryFrom<U256> for u8

impl TryFrom<U256> for u16

impl TryFrom<U256> for u32

impl TryFrom<U256> for usize

impl TryFrom<U256> for u64

impl TryFrom<U256> for i8

impl TryFrom<U256> for i16

impl TryFrom<U256> for i32

impl TryFrom<U256> for isize

impl TryFrom<U256> for i64

impl TryFrom<U256> for u128

impl TryFrom<U256> for i128

impl TryFrom<U512> for u8

impl TryFrom<U512> for u16

impl TryFrom<U512> for u32

impl TryFrom<U512> for usize

impl TryFrom<U512> for u64

impl TryFrom<U512> for i8

impl TryFrom<U512> for i16

impl TryFrom<U512> for i32

impl TryFrom<U512> for isize

impl TryFrom<U512> for i64

impl TryFrom<U512> for u128

impl TryFrom<U512> for i128

impl TryFrom<U256> for U128

impl TryFrom<U512> for U256

impl TryFrom<U512> for U128

impl<'a> TryFrom<&'a U512> for U256

impl<Size> TryFrom<&[u8]> for EncodedPoint<Size>where
    Size: ModulusSize,

impl<'a> TryFrom<&'a [u8]> for EcPrivateKey<'a>

impl TryFrom<i32> for Parity

impl TryFrom<u8> for Parity

impl TryFrom<u8> for OpCode

impl<'a> TryFrom<&'a [u8]> for ByteSlice125<'a>

impl<'a> TryFrom<&'a [u8]> for Public

impl<'a> TryFrom<&'a [u8]> for Signature

impl<'a> TryFrom<&'a [u8]> for Public

impl<'a> TryFrom<&'a [u8]> for Signature

impl<'a> TryFrom<&'a [u8]> for Public

impl<'a> TryFrom<&'a [u8]> for Signature

impl TryFrom<BigUint> for u128

impl TryFrom<BigUint> for u64

impl TryFrom<[u8; 32]> for VRFOutput

impl TryFrom<[u8; 64]> for VRFProof

impl<'a> TryFrom<&'a [u8]> for AccountId32

impl<'a> TryFrom<&'a [u8]> for Dummy

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

impl TryFrom<&[u8]> for Public

impl TryFrom<&[u8]> for Signature

impl TryFrom<&[u8]> for Public

impl TryFrom<&[u8]> for Signature

impl TryFrom<u8> for HttpError

impl TryFrom<&[u8]> for Public

impl TryFrom<&[u8]> for Signature

impl TryFrom<u8> for LogLevel

impl<K, V, S> TryFrom<BTreeMap<K, V, Global>> for BoundedBTreeMap<K, V, S>where
    K: Ord,
    S: Get<u32>,

impl<T, S> TryFrom<BTreeSet<T, Global>> for BoundedBTreeSet<T, S>where
    T: Ord,
    S: Get<u32>,

impl<'a, T, S: Get<u32>> TryFrom<&'a [T]> for BoundedSlice<'a, T, S>

impl<T, S: Get<u32>> TryFrom<Vec<T, Global>> for BoundedVec<T, S>

impl<T, S: Get<u32>> TryFrom<Vec<T, Global>> for WeakBoundedVec<T, S>

impl TryFrom<u8> for ValueType

impl<'a> TryFrom<&'a str> for Ss58AddressFormat

impl<T, A> TryFrom<&[T]> for ArrayVec<A>where
    T: Clone + Default,
    A: Array<Item = T>,

impl<'a, HO> TryFrom<NodeHandle<'a>> for ChildReference<HO>where
    HO: AsRef<[u8]> + AsMut<[u8]> + Default + Clone + Copy,

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

impl TryFrom<JsValue> for f64

impl TryFrom<&JsValue> for f64

impl TryFrom<JsValue> for i64

impl TryFrom<JsValue> for u64

impl TryFrom<JsValue> for i128

impl TryFrom<JsValue> for u128

impl<'a> TryFrom<&'a [u8]> for EndEntityCert<'a>

impl<T> TryFrom<*const T> for Address<Const, T>where
    T: ?Sized,

impl<T> TryFrom<*mut T> for Address<Mut, T>where
    T: ?Sized,

impl<Call> TryFrom<Order<Call>> for Order<Call>

impl<Call> TryFrom<Xcm<Call>> for Xcm<Call>

impl<Call> TryFrom<Order<Call>> for Order<Call>

impl<Call> TryFrom<Instruction<Call>> for Order<Call>

impl<Call> TryFrom<Xcm<Call>> for Xcm<Call>

impl<Call> TryFrom<Xcm<Call>> for Xcm<Call>

impl<Call> TryFrom<Xcm<Call>> for Xcm<Call>

impl<Call> TryFrom<Order<Call>> for Instruction<Call>

impl<Call> TryFrom<VersionedXcm<Call>> for Xcm<Call>

impl<Call> TryFrom<VersionedXcm<Call>> for Xcm<Call>

impl<Call> TryFrom<VersionedXcm<Call>> for Xcm<Call>