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,Borrowhas a blanket impl for anyT, and can be used to accept either a reference or a value. (See also note onAsRef’s reflexibility below.) Borrowalso requires thatHash,EqandOrdfor 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 implementAsRef, but notBorrow.
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<U> 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§
Implementors§
impl AsRef<str> for str
impl AsRef<str> for AcceptedWebSocketProtocol
impl AsRef<str> for LastEventId
impl AsRef<str> for Mime
impl AsRef<str> for RequestComment
impl AsRef<str> for HeaderName
impl AsRef<str> for Method
impl AsRef<str> for Scheme
impl AsRef<str> for Authority
impl AsRef<str> for Utf8Bytes
impl AsRef<str> for Domain
impl AsRef<str> for ProxyID
impl AsRef<str> for StringFilter
impl AsRef<str> for Key
impl AsRef<str> for StringValue
impl AsRef<str> for Field
impl AsRef<str> for OpensslString
impl AsRef<str> for OpensslStringRef
impl AsRef<str> for NonEmptyString
impl AsRef<str> for DnsName<'_>
impl AsRef<str> for rama::crypto::dep::rcgen::string::Ia5String
impl AsRef<str> for rama::crypto::dep::rcgen::string::PrintableString
impl AsRef<str> for rama::crypto::dep::rcgen::string::TeletexString
impl AsRef<str> for BmpString<'_>
impl AsRef<str> for UniversalString<'_>
impl AsRef<str> for String
impl AsRef<str> for Url
Return the serialization of this URL.
impl AsRef<str> for NormalizedPath<'_>
impl AsRef<str> for NormalizedPathBuf
impl AsRef<str> for SmolStr
impl AsRef<str> for UriTemplateStr
impl AsRef<str> for UriTemplateString
impl AsRef<str> for ZipFilePath<NormalizedPath<'_>>
impl AsRef<str> for ZipFilePath<NormalizedPathBuf>
impl AsRef<Bytes> for Utf8Bytes
impl AsRef<Extensions> for RequestContextExt
impl AsRef<InMemoryDns> for DnsOverwrite
impl AsRef<HeaderMap> for HttpProxyConnectResponseHeaders
impl AsRef<SocketInfo> for ClientSocketInfo
impl AsRef<TcpStream> for OwnedReadHalf
impl AsRef<TcpStream> for OwnedWriteHalf
impl AsRef<TcpStream> for ReadHalf<'_>
impl AsRef<TcpStream> for WriteHalf<'_>
impl AsRef<Asn1BitStringRef> for Asn1BitString
impl AsRef<Asn1GeneralizedTimeRef> for Asn1GeneralizedTime
impl AsRef<Asn1IntegerRef> for Asn1Integer
impl AsRef<Asn1ObjectRef> for Asn1Object
impl AsRef<Asn1StringRef> for Asn1String
impl AsRef<Asn1TimeRef> for Asn1Time
impl AsRef<BigNumContextRef> for BigNumContext
impl AsRef<BigNumRef> for BigNum
impl AsRef<ConfRef> for Conf
impl AsRef<EcGroupRef> for EcGroup
impl AsRef<EcPointRef> for EcPoint
impl AsRef<EcdsaSigRef> for EcdsaSig
impl AsRef<HpkeKeyRef> for HpkeKey
impl AsRef<Pkcs12Ref> for Pkcs12
impl AsRef<SrtpProtectionProfileRef> for SrtpProtectionProfile
impl AsRef<SslContextRef> for SslContext
impl AsRef<SslEchKeysRef> for SslEchKeys
impl AsRef<SslRef> for Ssl
impl AsRef<SslSessionRef> for SslSession
impl AsRef<OpensslStringRef> for OpensslString
impl AsRef<X509StoreBuilderRef> for X509StoreBuilder
impl AsRef<X509StoreRef> for X509Store
impl AsRef<GeneralNameRef> for GeneralName
impl AsRef<X509AlgorithmRef> for X509Algorithm
impl AsRef<X509ExtensionRef> for X509Extension
impl AsRef<X509NameEntryRef> for X509NameEntry
impl AsRef<X509NameRef> for X509Name
impl AsRef<X509ObjectRef> for X509Object
impl AsRef<X509Ref> for X509
impl AsRef<X509Ref> for X509Ref
impl AsRef<X509ReqRef> for X509Req
impl AsRef<X509StoreContextRef> for X509StoreContext
impl AsRef<X509VerifyParamRef> for X509VerifyParam
impl AsRef<UnixSocketInfo> for ClientUnixSocketInfo
impl AsRef<UnixStream> for OwnedReadHalf
impl AsRef<UnixStream> for OwnedWriteHalf
impl AsRef<UnixStream> for ReadHalf<'_>
impl AsRef<UnixStream> for WriteHalf<'_>
impl AsRef<CertificateParams> for CertificateParams
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 String
impl AsRef<OsStr> for OsStr
impl AsRef<OsStr> for OsString
impl AsRef<OsStr> for Components<'_>
impl AsRef<OsStr> for std::path::Iter<'_>
impl AsRef<OsStr> for Path
impl AsRef<OsStr> for PathBuf
impl AsRef<OsStr> for SmolStr
impl AsRef<Path> for Cow<'_, OsStr>
impl AsRef<Path> for Component<'_>
impl AsRef<Path> for str
impl AsRef<Path> for HarFilePath
impl AsRef<Path> for String
impl AsRef<Path> for OsStr
impl AsRef<Path> for OsString
impl AsRef<Path> for Components<'_>
impl AsRef<Path> for std::path::Iter<'_>
impl AsRef<Path> for Path
impl AsRef<Path> for PathBuf
impl AsRef<Path> for SmolStr
impl AsRef<Uuid> for Braced
impl AsRef<Uuid> for Hyphenated
impl AsRef<Uuid> for Simple
impl AsRef<Uuid> for Urn
impl AsRef<Uuid> for Uuid
impl AsRef<Interval> for IntervalStream
impl AsRef<RiAbsoluteStr<IriSpec>> for RiAbsoluteStr<UriSpec>
impl AsRef<RiAbsoluteStr<IriSpec>> for RiAbsoluteString<UriSpec>
impl AsRef<RiFragmentStr<IriSpec>> for RiFragmentStr<UriSpec>
impl AsRef<RiFragmentStr<IriSpec>> for RiFragmentString<UriSpec>
impl AsRef<RiQueryStr<IriSpec>> for RiQueryStr<UriSpec>
impl AsRef<RiQueryStr<IriSpec>> for RiQueryString<UriSpec>
impl AsRef<RiReferenceStr<IriSpec>> for RiReferenceStr<UriSpec>
impl AsRef<RiReferenceStr<IriSpec>> for RiReferenceString<UriSpec>
impl AsRef<RiRelativeStr<IriSpec>> for RiRelativeStr<UriSpec>
impl AsRef<RiRelativeStr<IriSpec>> for RiRelativeString<UriSpec>
impl AsRef<RiStr<IriSpec>> for RiStr<UriSpec>
impl AsRef<RiStr<IriSpec>> for RiString<UriSpec>
impl AsRef<Semaphore> for PollSemaphore
impl AsRef<UriTemplateStr> for UriTemplateStr
impl AsRef<UriTemplateStr> for UriTemplateString
impl AsRef<[(EdnsCode, EdnsOption)]> for OPT
impl AsRef<[u8; 4]> for Ipv4Addr
impl AsRef<[u8; 12]> for Nonce
impl AsRef<[u8; 16]> for Ipv6Addr
impl AsRef<[u8]> for str
impl AsRef<[u8]> for Bytes
impl AsRef<[u8]> for BytesMut
impl AsRef<[u8]> for ReasonPhrase
impl AsRef<[u8]> for Upgrade
impl AsRef<[u8]> for rama::http::proto::h2::ext::Protocol
impl AsRef<[u8]> for HeaderName
impl AsRef<[u8]> for HeaderValue
impl AsRef<[u8]> for Utf8Bytes
impl AsRef<[u8]> for DigestBytes
impl AsRef<[u8]> for OpensslString
impl AsRef<[u8]> for OpensslStringRef
impl AsRef<[u8]> for AeadKey
impl AsRef<[u8]> for Iv
impl AsRef<[u8]> for PrefixedPayload
impl AsRef<[u8]> for Output
impl AsRef<[u8]> for rama::tls::rustls::dep::rustls::crypto::hmac::Tag
impl AsRef<[u8]> for OkmBlock
impl AsRef<[u8]> for rama::tls::rustls::dep::rustls::quic::Tag
impl AsRef<[u8]> for DistinguishedName
impl AsRef<[u8]> for rama::crypto::dep::aws_lc_rs::aead::Tag
impl AsRef<[u8]> for rama::crypto::dep::aws_lc_rs::agreement::PublicKey
impl AsRef<[u8]> for Digest
impl AsRef<[u8]> for rama::crypto::dep::aws_lc_rs::hmac::Tag
impl AsRef<[u8]> for Ciphertext<'_>
impl AsRef<[u8]> for Document
impl AsRef<[u8]> for rama::crypto::dep::aws_lc_rs::signature::EcdsaPublicKey
impl AsRef<[u8]> for rama::crypto::dep::aws_lc_rs::signature::Ed25519PublicKey
impl AsRef<[u8]> for rama::crypto::dep::aws_lc_rs::signature::RsaSubjectPublicKey
impl AsRef<[u8]> for Signature
impl AsRef<[u8]> for Secret
impl AsRef<[u8]> for AlgorithmIdentifier
impl AsRef<[u8]> for CertificateDer<'_>
impl AsRef<[u8]> for CertificateRevocationListDer<'_>
impl AsRef<[u8]> for CertificateSigningRequestDer<'_>
impl AsRef<[u8]> for Der<'_>
impl AsRef<[u8]> for EchConfigListBytes<'_>
impl AsRef<[u8]> for SubjectPublicKeyInfoDer<'_>
impl AsRef<[u8]> for SerialNumber
impl AsRef<[u8]> for TbsCertificate<'_>
impl AsRef<[u8]> for BitStringObject<'_>
impl AsRef<[u8]> for TbsCertList<'_>
impl AsRef<[u8]> for BitString<'_>
impl AsRef<[u8]> for Integer<'_>
impl AsRef<[u8]> for OctetString<'_>
impl AsRef<[u8]> for Sequence<'_>
impl AsRef<[u8]> for Set<'_>
impl AsRef<[u8]> for String
impl AsRef<[u8]> for ByteString
impl AsRef<[u8]> for ByteStr
impl AsRef<[u8]> for Uuid
impl AsRef<[u8]> for Label
impl AsRef<[u8]> for Literal
impl AsRef<[u8]> for NormalizedPath<'_>
impl AsRef<[u8]> for NormalizedPathBuf
impl AsRef<[u8]> for Protocol
impl AsRef<[u8]> for RawPath<'_>
impl AsRef<[u8]> for SmolStr
impl AsRef<[u8]> for ZipFilePath<RawPath<'_>>
impl AsRef<[u64]> for ObjectIdentifier
impl<'a> AsRef<str> for Name<'a>
impl<'a> AsRef<str> for GeneralString<'a>
impl<'a> AsRef<str> for GraphicString<'a>
impl<'a> AsRef<str> for rama::crypto::dep::x509_parser::prelude::asn1_rs::Ia5String<'a>
impl<'a> AsRef<str> for NumericString<'a>
impl<'a> AsRef<str> for ObjectDescriptor<'a>
impl<'a> AsRef<str> for rama::crypto::dep::x509_parser::prelude::asn1_rs::PrintableString<'a>
impl<'a> AsRef<str> for rama::crypto::dep::x509_parser::prelude::asn1_rs::TeletexString<'a>
impl<'a> AsRef<str> for Utf8String<'a>
impl<'a> AsRef<str> for VideotexString<'a>
impl<'a> AsRef<str> for VisibleString<'a>
impl<'a> AsRef<str> for rama::crypto::dep::x509_parser::prelude::asn1_rs::nom::lib::std::string::Drain<'a>
impl<'a> AsRef<[u8]> for X509Certificate<'a>
impl<'a> AsRef<[u8]> for X509CertificationRequest<'a>
impl<'a> AsRef<[u8]> for CertificateRevocationList<'a>
impl<'a> AsRef<[u8]> for rama::crypto::dep::x509_parser::prelude::asn1_rs::nom::lib::std::string::Drain<'a>
impl<'a, S> AsRef<Certificate> for CertifiedIssuer<'a, S>
impl<'a, T> AsRef<ZeroSlice<T>> for ZeroVec<'a, T>where
T: AsULE,
impl<'a, T> AsRef<[<T as AsULE>::ULE]> for ZeroVec<'a, T>where
T: AsULE,
impl<'a, T, A> AsRef<[T]> for rama::crypto::dep::x509_parser::prelude::asn1_rs::nom::lib::std::vec::Drain<'a, T, A>where
A: Allocator,
impl<'a, T, A> AsRef<[T]> for Drain<'a, T, A>where
A: Allocator,
impl<'s, T> AsRef<[T]> for SliceVec<'s, T>
impl<A> AsRef<[<A as Array>::Item]> for ArrayVec<A>where
A: Array,
impl<A> AsRef<[<A as Array>::Item]> for SmallVec<A>where
A: Array,
impl<A> AsRef<[<A as Array>::Item]> for TinyVec<A>where
A: Array,
impl<A> AsRef<[u8]> for Aad<A>
impl<B> AsRef<[u8]> for UnparsedPublicKey<B>
impl<C> AsRef<C> for Authorization<C>
impl<C, ID> AsRef<C> for LeasedConnection<C, ID>
impl<L, R> AsRef<str> for Either<L, R>
impl<L, R> AsRef<CStr> for Either<L, R>
Requires crate feature std.
impl<L, R> AsRef<OsStr> for Either<L, R>
Requires crate feature std.
impl<L, R> AsRef<Path> for Either<L, R>
Requires crate feature std.