Trait AsRef

1.0.0 (const: unstable) · Source

pub trait AsRef<T>where
    T: ?Sized,{
    // Required method
    fn as_ref(&self) -> &T;
}

Expand description

Used to do a cheap reference-to-reference conversion.

This trait is similar to AsMut which is used for converting between mutable references. If you need to do a costly conversion it is better to implement From with type &T or write a custom function.

§Relation to `Borrow`

AsRef has the same signature as Borrow, but Borrow is different in a few aspects:

Unlike AsRef, Borrow has a blanket impl for any T, and can be used to accept either a reference or a value. (See also note on AsRef’s reflexibility below.)
Borrow also requires that Hash, Eq and Ord for a borrowed value are equivalent to those of the owned value. For this reason, if you want to borrow only a single field of a struct you can implement AsRef, but not Borrow.

Note: This trait must not fail. If the conversion can fail, use a dedicated method which returns an Option<T> or a Result<T, E>.

§Generic Implementations

AsRef auto-dereferences if the inner type is a reference or a mutable reference (e.g.: foo.as_ref() will work the same if foo has type &mut Foo or &&mut Foo).

Note that due to historic reasons, the above currently does not hold generally for all dereferenceable types, e.g. foo.as_ref() will not work the same as Box::new(foo).as_ref(). Instead, many smart pointers provide an as_ref implementation which simply returns a reference to the pointed-to value (but do not perform a cheap reference-to-reference conversion for that value). However, AsRef::as_ref should not be used for the sole purpose of dereferencing; instead ‘Deref coercion’ can be used:

let x = Box::new(5i32);
// Avoid this:
// let y: &i32 = x.as_ref();
// Better just write:
let y: &i32 = &x;

Types which implement Deref should consider implementing AsRef<T> as follows:

impl<T> AsRef<T> for SomeType
where
    T: ?Sized,
    <SomeType as Deref>::Target: AsRef<T>,
{
    fn as_ref(&self) -> &T {
        self.deref().as_ref()
    }
}

§Reflexivity

Ideally, AsRef would be reflexive, i.e. there would be an impl<T: ?Sized> AsRef<T> for T with as_ref simply returning its argument unchanged. Such a blanket implementation is currently not provided due to technical restrictions of Rust’s type system (it would be overlapping with another existing blanket implementation for &T where T: AsRef which allows AsRef to auto-dereference, see “Generic Implementations” above).

A trivial implementation of AsRef<T> for T must be added explicitly for a particular type T where needed or desired. Note, however, that not all types from std contain such an implementation, and those cannot be added by external code due to orphan rules.

§Examples

By using trait bounds we can accept arguments of different types as long as they can be converted to the specified type T.

For example: By creating a generic function that takes an AsRef<str> we express that we want to accept all references that can be converted to &str as an argument. Since both String and &str implement AsRef<str> we can accept both as input argument.

fn is_hello<T: AsRef<str>>(s: T) {
   assert_eq!("hello", s.as_ref());
}

let s = "hello";
is_hello(s);

let s = "hello".to_string();
is_hello(s);

Required Methods§

1.0.0 · Source

fn as_ref(&self) -> &T

Converts this type into a shared reference of the (usually inferred) input type.

AsRef

Trait AsRef Copy item path

§Relation to Borrow

§Generic Implementations

§Reflexivity

§Examples

Required Methods§

fn as_ref(&self) -> &T

Implementors§

impl AsRef<ConsensusManagerConfigurationVersions> for VersionedConsensusManagerConfiguration

impl AsRef<ConsensusManagerCurrentProposalStatisticVersions> for VersionedConsensusManagerCurrentProposalStatistic

impl AsRef<ConsensusManagerCurrentValidatorSetVersions> for VersionedConsensusManagerCurrentValidatorSet

impl AsRef<ConsensusManagerProposerMilliTimestampVersions> for VersionedConsensusManagerProposerMilliTimestamp

impl AsRef<ConsensusManagerProposerMinuteTimestampVersions> for VersionedConsensusManagerProposerMinuteTimestamp

impl AsRef<ConsensusManagerRegisteredValidatorByStakeVersions> for VersionedConsensusManagerRegisteredValidatorByStake

impl AsRef<ConsensusManagerStateVersions> for VersionedConsensusManagerState

impl AsRef<ConsensusManagerValidatorRewardsVersions> for VersionedConsensusManagerValidatorRewards

impl AsRef<FungibleResourceManagerDivisibilityVersions> for VersionedFungibleResourceManagerDivisibility

impl AsRef<FungibleResourceManagerTotalSupplyVersions> for VersionedFungibleResourceManagerTotalSupply

impl AsRef<FungibleVaultBalanceVersions> for VersionedFungibleVaultBalance

impl AsRef<FungibleVaultFreezeStatusVersions> for VersionedFungibleVaultFreezeStatus

impl AsRef<FungibleVaultLockedBalanceVersions> for VersionedFungibleVaultLockedBalance

impl AsRef<LedgerTransactionHashesVersions> for VersionedLedgerTransactionHashes

impl AsRef<NonFungibleLocalId> for NonFungibleResourceManagerDataKeyPayload

impl AsRef<NonFungibleLocalId> for NonFungibleVaultNonFungibleKeyPayload

impl AsRef<NonFungibleResourceManagerIdTypeVersions> for VersionedNonFungibleResourceManagerIdType

impl AsRef<NonFungibleResourceManagerMutableFieldsVersions> for VersionedNonFungibleResourceManagerMutableFields

impl AsRef<NonFungibleResourceManagerTotalSupplyVersions> for VersionedNonFungibleResourceManagerTotalSupply

impl AsRef<NonFungibleVaultBalanceVersions> for VersionedNonFungibleVaultBalance

impl AsRef<NonFungibleVaultFreezeStatusVersions> for VersionedNonFungibleVaultFreezeStatus

impl AsRef<NonFungibleVaultLockedResourceVersions> for VersionedNonFungibleVaultLockedResource

impl AsRef<NonFungibleVaultNonFungibleVersions> for VersionedNonFungibleVaultNonFungible

impl AsRef<PackageBlueprintVersionAuthConfigVersions> for VersionedPackageBlueprintVersionAuthConfig

impl AsRef<PackageBlueprintVersionDefinitionVersions> for VersionedPackageBlueprintVersionDefinition

impl AsRef<PackageBlueprintVersionDependenciesVersions> for VersionedPackageBlueprintVersionDependencies

impl AsRef<PackageBlueprintVersionRoyaltyConfigVersions> for VersionedPackageBlueprintVersionRoyaltyConfig

impl AsRef<PackageCodeInstrumentedCodeVersions> for VersionedPackageCodeInstrumentedCode

impl AsRef<PackageCodeOriginalCodeVersions> for VersionedPackageCodeOriginalCode

impl AsRef<PackageCodeVmTypeVersions> for VersionedPackageCodeVmType

impl AsRef<PackageRoyaltyAccumulatorVersions> for VersionedPackageRoyaltyAccumulator

impl AsRef<ProtocolUpdateStatusSummaryVersions> for ProtocolUpdateStatusSummarySubstate

impl AsRef<ResourceOrNonFungible> for AccountAuthorizedDepositorKeyPayload

impl AsRef<ValidatorProtocolUpdateReadinessSignalVersions> for VersionedValidatorProtocolUpdateReadinessSignal

impl AsRef<ValidatorStateVersions> for VersionedValidatorState

impl AsRef<AccountAuthorizedDepositorVersions> for VersionedAccountAuthorizedDepositor

impl AsRef<AccountDepositRuleVersions> for VersionedAccountDepositRule

impl AsRef<AccountResourcePreferenceVersions> for VersionedAccountResourcePreference

impl AsRef<AccountResourceVaultVersions> for VersionedAccountResourceVault

impl AsRef<AccountLockerAccountClaimsVersions> for VersionedAccountLockerAccountClaims

impl AsRef<MetadataEntryVersions> for VersionedMetadataEntry

impl AsRef<RoleAssignmentAccessRuleVersions> for VersionedRoleAssignmentAccessRule

impl AsRef<RoleAssignmentOwnerVersions> for VersionedRoleAssignmentOwner

impl AsRef<ComponentRoyaltyAccumulatorVersions> for VersionedComponentRoyaltyAccumulator

impl AsRef<ComponentRoyaltyMethodAmountVersions> for VersionedComponentRoyaltyMethodAmount

impl AsRef<TreeNodeVersions> for VersionedTreeNode

impl AsRef<TransactionValidationConfigurationVersions> for TransactionValidationConfigurationSubstate

impl AsRef<MultiResourcePoolStateVersions> for VersionedMultiResourcePoolState

impl AsRef<OneResourcePoolStateVersions> for VersionedOneResourcePoolState

impl AsRef<TwoResourcePoolStateVersions> for VersionedTwoResourcePoolState

impl AsRef<AccessControllerStateVersions> for VersionedAccessControllerState

impl AsRef<AccessControllerV2StateVersions> for VersionedAccessControllerV2State

impl AsRef<str> for str

impl AsRef<str> for AliasableString

impl AsRef<str> for InternalString

impl AsRef<str> for String

impl AsRef<u8> for u5

impl AsRef<ByteStr> for str

impl AsRef<ByteStr> for ByteString

impl AsRef<ByteStr> for ByteStr

impl AsRef<CStr> for CString

impl AsRef<CStr> for CStr

impl AsRef<LocalWaker> for Waker

impl AsRef<OsStr> for Component<'_>

impl AsRef<OsStr> for str

impl AsRef<OsStr> for OsStr

impl AsRef<OsStr> for std::ffi::os_str::OsString

impl AsRef<OsStr> for Components<'_>

impl AsRef<OsStr> for std::path::Iter<'_>

impl AsRef<OsStr> for Path

impl AsRef<OsStr> for PathBuf

Trait AsRef

§Relation to `Borrow`