Trait bitflags::__core::marker::Copy 1.0.0
[−]
[src]
pub trait Copy: Clone { }
Types that can be copied by simply copying bits (i.e. memcpy
).
By default, variable bindings have 'move semantics.' In other words:
#[derive(Debug)] struct Foo; let x = Foo; let y = x; // `x` has moved into `y`, and so cannot be used // println!("{:?}", x); // error: use of moved value
However, if a type implements Copy
, it instead has 'copy semantics':
// we can just derive a `Copy` implementation #[derive(Debug, Copy, Clone)] struct Foo; let x = Foo; let y = x; // `y` is a copy of `x` println!("{:?}", x); // A-OK!
It's important to note that in these two examples, the only difference is if you are allowed to
access x
after the assignment: a move is also a bitwise copy under the hood.
When can my type be Copy
?
A type can implement Copy
if all of its components implement Copy
. For example, this
struct
can be Copy
:
struct Point { x: i32, y: i32, }
A struct
can be Copy
, and i32
is Copy
, so therefore, Point
is eligible to be Copy
.
struct PointList { points: Vec<Point>, }
The PointList
struct
cannot implement Copy
, because Vec<T>
is not Copy
. If we
attempt to derive a Copy
implementation, we'll get an error:
the trait `Copy` may not be implemented for this type; field `points` does not implement `Copy`
When can my type not be Copy
?
Some types can't be copied safely. For example, copying &mut T
would create an aliased
mutable reference, and copying String
would result in two attempts to free the same buffer.
Generalizing the latter case, any type implementing Drop
can't be Copy
, because it's
managing some resource besides its own size_of::<T>()
bytes.
When should my type be Copy
?
Generally speaking, if your type can implement Copy
, it should. There's one important thing
to consider though: if you think your type may not be able to implement Copy
in the future,
then it might be prudent to not implement Copy
. This is because removing Copy
is a breaking
change: that second example would fail to compile if we made Foo
non-Copy
.
Derivable
This trait can be used with #[derive]
if all of its components implement Copy
and the type
implements Clone
. The implementation will copy the bytes of each field using memcpy
.
How can I implement Copy
?
There are two ways to implement Copy
on your type:
#[derive(Copy, Clone)] struct MyStruct;
and
struct MyStruct; impl Copy for MyStruct {} impl Clone for MyStruct { fn clone(&self) -> MyStruct { *self } }
There is a small difference between the two: the derive
strategy will also place a Copy
bound on type parameters, which isn't always desired.
Implementors
impl<T> Copy for Wrapping<T> where T: Copy
impl Copy for FpCategory
impl Copy for TryFromIntError
impl<T> Copy for NonZero<T> where T: Copy + Zeroable
impl<T> Copy for Shared<T> where T: ?Sized
impl<T> Copy for PhantomData<T> where T: ?Sized
impl Copy for RangeFull
impl<Idx> Copy for RangeTo<Idx> where Idx: Copy
impl<Idx> Copy for RangeInclusive<Idx> where Idx: Copy
impl<Idx> Copy for RangeToInclusive<Idx> where Idx: Copy
impl Copy for Ordering
impl Copy for TypeId
impl Copy for Ordering
impl Copy for BorrowState
impl<T> Copy for Option<T> where T: Copy
impl Copy for TraitObject
impl<T, E> Copy for Result<T, E> where E: Copy, T: Copy
impl Copy for SearchStep
impl Copy for Utf8Error
impl Copy for CharRange
impl Copy for Error
impl<'a> Copy for Arguments<'a>
impl Copy for Error
impl<T: Copy> Copy for Status<T>
impl<'a> Copy for Header<'a>
impl Copy for pthread_attr_t
impl Copy for glob_t
impl Copy for sockaddr_storage
impl Copy for addrinfo
impl Copy for mach_timebase_info
impl Copy for stat
impl Copy for dirent
impl Copy for pthread_mutex_t
impl Copy for pthread_mutexattr_t
impl Copy for pthread_cond_t
impl Copy for pthread_rwlock_t
impl Copy for siginfo_t
impl Copy for sigaction
impl Copy for stack_t
impl Copy for fstore_t
impl Copy for radvisory
impl Copy for statvfs
impl Copy for Dl_info
impl Copy for sockaddr_in
impl Copy for statfs
impl Copy for kevent
impl Copy for kevent64_s
impl Copy for dqblk
impl Copy for termios
impl Copy for flock
impl Copy for sf_hdtr
impl Copy for lconv
impl Copy for sockaddr
impl Copy for sockaddr_in6
impl Copy for sockaddr_un
impl Copy for passwd
impl Copy for ifaddrs
impl Copy for fd_set
impl Copy for tm
impl Copy for utsname
impl Copy for msghdr
impl Copy for fsid_t
impl Copy for utimbuf
impl Copy for timeval
impl Copy for timespec
impl Copy for rlimit
impl Copy for rusage
impl Copy for in_addr
impl Copy for in6_addr
impl Copy for ip_mreq
impl Copy for ipv6_mreq
impl Copy for hostent
impl Copy for iovec
impl Copy for pollfd
impl Copy for winsize
impl Copy for LogLevel
impl Copy for LogLevelFilter
impl Copy for LogLocation
impl Copy for NopErrorHandler
impl Copy for LoggingErrorHandler
impl Copy for NopConnectionCustomizer
impl Copy for IntegerDecodingError
impl Copy for StringDecodingError
impl Copy for DecoderError
impl Copy for HuffmanDecoderError
impl<X: Copy> Copy for Range<X>
impl Copy for Gamma
impl Copy for ChiSquared
impl Copy for FisherF
impl Copy for StudentT
impl Copy for StandardNormal
impl Copy for Normal
impl Copy for LogNormal
impl Copy for Exp1
impl Copy for Exp
impl<Sup> Copy for RandSample<Sup>
impl<T: Copy> Copy for Weighted<T>
impl Copy for IsaacRng
impl Copy for Isaac64Rng
impl Copy for ChaChaRng
impl Copy for ReseedWithDefault
impl Copy for StdRng
impl Copy for DataFlag
impl Copy for HeadersFlag
impl Copy for HttpSetting
impl Copy for SettingsFlag
impl Copy for SendStatus
impl Copy for EndStream
impl Copy for StreamState
impl Copy for StreamDataChunk
impl Copy for HttpScheme
impl Copy for Duration
impl Copy for OutOfRangeError
impl Copy for Timespec
impl Copy for PreciseTime
impl Copy for SteadyTime
impl Copy for Tm
impl Copy for ParseError
impl Copy for BIO_METHOD
impl Copy for EVP_MD_CTX
impl Copy for HMAC_CTX
impl Copy for GENERAL_NAME
impl Copy for X509V3_CTX
impl Copy for BIGNUM
impl<E> Copy for EnumSet<E>
impl Copy for ParseError
impl<T> Copy for Bound<T> where T: Copy
impl Copy for ExchangeHeapSingleton
impl Copy for Repeater
impl Copy for ClassRange
impl Copy for ByteRange
impl Copy for BidiClass
impl Copy for Flags
impl Copy for RNGProperty
impl Copy for Type
impl Copy for Parts
impl Copy for Role
impl Copy for EncryptionPadding
impl Copy for Mode
impl Copy for Type
impl Copy for SslContextOptions
impl Copy for SslMethod
impl Copy for SslVerifyMode
impl Copy for LocalKeyState
impl Copy for FileType
impl Copy for ErrorKind
impl Copy for SeekFrom
impl Copy for IpAddr
impl Copy for Ipv4Addr
impl Copy for Ipv6Addr
impl Copy for Ipv6MulticastScope
impl Copy for SocketAddr
impl Copy for SocketAddrV4
impl Copy for SocketAddrV6
impl Copy for Shutdown
impl<'a> Copy for Prefix<'a>
impl<'a> Copy for PrefixComponent<'a>
impl<'a> Copy for Component<'a>
impl Copy for ExitStatus
impl<T> Copy for SendError<T> where T: Copy
impl Copy for RecvError
impl Copy for TryRecvError
impl<T> Copy for TrySendError<T> where T: Copy
impl Copy for WaitTimeoutResult
impl Copy for Duration
impl Copy for Instant
impl Copy for SystemTime
impl Copy for utimbuf
impl Copy for timeval
impl Copy for timespec
impl Copy for rlimit
impl Copy for rusage
impl Copy for in_addr
impl Copy for in6_addr
impl Copy for ip_mreq
impl Copy for ipv6_mreq
impl Copy for hostent
impl Copy for iovec
impl Copy for pollfd
impl Copy for winsize
impl Copy for sockaddr
impl Copy for sockaddr_in6
impl Copy for sockaddr_un
impl Copy for passwd
impl Copy for ifaddrs
impl Copy for fd_set
impl Copy for tm
impl Copy for utsname
impl Copy for msghdr
impl Copy for fsid_t
impl Copy for glob_t
impl Copy for sockaddr_storage
impl Copy for addrinfo
impl Copy for mach_timebase_info
impl Copy for stat
impl Copy for dirent
impl Copy for pthread_mutex_t
impl Copy for pthread_mutexattr_t
impl Copy for pthread_cond_t
impl Copy for pthread_rwlock_t
impl Copy for siginfo_t
impl Copy for sigaction
impl Copy for stack_t
impl Copy for fstore_t
impl Copy for radvisory
impl Copy for statvfs
impl Copy for Dl_info
impl Copy for sockaddr_in
impl Copy for statfs
impl Copy for kevent
impl Copy for kevent64_s
impl Copy for dqblk
impl Copy for termios
impl Copy for flock
impl Copy for sf_hdtr
impl Copy for lconv
impl Copy for pthread_attr_t
impl Copy for ExchangeHeapSingleton
impl Copy for ParseError
impl Copy for KeyUsageOption
impl Copy for AltNameOption
impl Copy for X509FileType
impl Copy for X509ValidationError
impl Copy for Nid
impl Copy for CharacterSet
impl Copy for Newline
impl Copy for Config
impl Copy for FromBase64Error
impl Copy for FromHexError
impl Copy for ErrorCode
impl Copy for EncoderError
impl<E> Copy for EnumSet<E>
impl Copy for ParseError
impl<T> Copy for Bound<T> where T: Copy
impl Copy for ExchangeHeapSingleton
impl<'a> Copy for Bytes<'a>
impl Copy for Type
impl Copy for Match
impl<S: Copy> Copy for UniCase<S>
impl Copy for ParseError
impl Copy for Position
impl<'a> Copy for Parse<'a>
impl Copy for SIMPLE_ENCODE_SET
impl Copy for QUERY_ENCODE_SET
impl Copy for DEFAULT_ENCODE_SET
impl Copy for PATH_SEGMENT_ENCODE_SET
impl Copy for USERINFO_ENCODE_SET
impl<'a> Copy for ParseOptions<'a>
impl Copy for Utf8Sequence
impl Copy for Utf8Range
impl Copy for UuidVersion
impl Copy for UuidVariant
impl Copy for Uuid
impl Copy for ParseError
impl Copy for InputAt
impl<'t> Copy for CharInput<'t>
impl Copy for Char
impl Copy for EmptyLook
impl Copy for ParseError
impl Copy for Position
impl<'a> Copy for Parse<'a>
impl Copy for SIMPLE_ENCODE_SET
impl Copy for QUERY_ENCODE_SET
impl Copy for DEFAULT_ENCODE_SET
impl Copy for PATH_SEGMENT_ENCODE_SET
impl Copy for USERINFO_ENCODE_SET
impl<'a> Copy for ParseOptions<'a>
impl Copy for Flags
impl Copy for RedirectPolicy
impl Copy for HTTP_VALUE
impl Copy for StatusCode
impl Copy for StatusClass
impl Copy for HttpVersion
impl Copy for RedirectPolicy
impl<E> Copy for EnumSet<E>
impl Copy for ParseError
impl<T> Copy for Bound<T> where T: Copy
impl Copy for ExchangeHeapSingleton
impl Copy for ContentLength
impl Copy for Expect
impl Copy for HttpDate
impl Copy for Quality
impl Copy for HTTP_VALUE
impl Copy for StatusCode
impl Copy for StatusClass
impl Copy for HttpVersion