1.0.0[−][src]Trait boolean_enums::lstd::prelude::v1::Copy
Types whose values can be duplicated simply by copying bits.
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 derive a `Copy` implementation. `Clone` is also required, as it's // a supertrait of `Copy`. #[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 whether you
are allowed to access x
after the assignment. Under the hood, both a copy and a move
can result in bits being copied in memory, although this is sometimes optimized away.
How can I implement Copy
?
There are two ways to implement Copy
on your type. The simplest is to use derive
:
#[derive(Copy, Clone)] struct MyStruct;
You can also implement Copy
and Clone
manually:
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.
What's the difference between Copy
and Clone
?
Copies happen implicitly, for example as part of an assignment y = x
. The behavior of
Copy
is not overloadable; it is always a simple bit-wise copy.
Cloning is an explicit action, x.clone()
. The implementation of Clone
can
provide any type-specific behavior necessary to duplicate values safely. For example,
the implementation of Clone
for String
needs to copy the pointed-to string
buffer in the heap. A simple bitwise copy of String
values would merely copy the
pointer, leading to a double free down the line. For this reason, String
is Clone
but not Copy
.
Clone
is a supertrait of Copy
, so everything which is Copy
must also implement
Clone
. If a type is Copy
then its Clone
implementation only needs to return *self
(see the example above).
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
, therefore Point
is eligible to be Copy
.
By contrast, consider
struct PointList { points: Vec<Point>, }
The struct PointList
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't my type be Copy
?
Some types can't be copied safely. For example, copying &mut T
would create an aliased
mutable reference. Copying String
would duplicate responsibility for managing the
String
's buffer, leading to a double free.
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.
If you try to implement Copy
on a struct or enum containing non-Copy
data, you will get
the error E0204.
When should my type be Copy
?
Generally speaking, if your type can implement Copy
, it should. Keep in mind, though,
that implementing Copy
is part of the public API of your type. If the type might become
non-Copy
in the future, it could be prudent to omit the Copy
implementation now, to
avoid a breaking API change.
Additional implementors
In addition to the implementors listed below,
the following types also implement Copy
:
- Function item types (i.e., the distinct types defined for each function)
- Function pointer types (e.g.,
fn() -> i32
) - Array types, for all sizes, if the item type also implements
Copy
(e.g.,[i32; 123456]
) - Tuple types, if each component also implements
Copy
(e.g.,()
,(i32, bool)
) - Closure types, if they capture no value from the environment
or if all such captured values implement
Copy
themselves. Note that variables captured by shared reference always implementCopy
(even if the referent doesn't), while variables captured by mutable reference never implementCopy
.
Implementations on Foreign Types
impl Copy for u16
[src]
impl Copy for u16
impl Copy for i8
[src]
impl Copy for i8
impl Copy for char
[src]
impl Copy for char
impl Copy for f64
[src]
impl Copy for f64
impl Copy for u128
[src]
impl Copy for u128
impl Copy for i32
[src]
impl Copy for i32
impl Copy for i16
[src]
impl Copy for i16
impl Copy for TryFromSliceError
[src]
impl Copy for TryFromSliceError
impl Copy for i64
[src]
impl Copy for i64
impl<'_, T> Copy for &'_ T where
T: ?Sized,
[src]
impl<'_, T> Copy for &'_ T where
T: ?Sized,
impl Copy for f32
[src]
impl Copy for f32
impl<T> Copy for *mut T where
T: ?Sized,
[src]
impl<T> Copy for *mut T where
T: ?Sized,
impl<T> Copy for *const T where
T: ?Sized,
[src]
impl<T> Copy for *const T where
T: ?Sized,
impl Copy for usize
[src]
impl Copy for usize
impl Copy for !
[src]
impl Copy for !
impl Copy for u32
[src]
impl Copy for u32
impl Copy for bool
[src]
impl Copy for bool
impl Copy for i128
[src]
impl Copy for i128
impl Copy for u8
[src]
impl Copy for u8
impl Copy for u64
[src]
impl Copy for u64
impl Copy for isize
[src]
impl Copy for isize
impl Copy for Elf32_Sym
[src]
impl Copy for Elf32_Sym
impl Copy for stack_t
[src]
impl Copy for stack_t
impl Copy for in_pktinfo
[src]
impl Copy for in_pktinfo
impl Copy for Elf64_Phdr
[src]
impl Copy for Elf64_Phdr
impl Copy for pthread_mutexattr_t
[src]
impl Copy for pthread_mutexattr_t
impl Copy for arpreq
[src]
impl Copy for arpreq
impl Copy for nl_pktinfo
[src]
impl Copy for nl_pktinfo
impl Copy for Elf64_Chdr
[src]
impl Copy for Elf64_Chdr
impl Copy for sockaddr_in
[src]
impl Copy for sockaddr_in
impl Copy for mntent
[src]
impl Copy for mntent
impl Copy for timespec
[src]
impl Copy for timespec
impl Copy for pthread_rwlockattr_t
[src]
impl Copy for pthread_rwlockattr_t
impl Copy for ifaddrs
[src]
impl Copy for ifaddrs
impl Copy for sigevent
[src]
impl Copy for sigevent
impl Copy for _libc_fpreg
[src]
impl Copy for _libc_fpreg
impl Copy for Elf32_Phdr
[src]
impl Copy for Elf32_Phdr
impl Copy for hostent
[src]
impl Copy for hostent
impl Copy for cpu_set_t
[src]
impl Copy for cpu_set_t
impl Copy for arphdr
[src]
impl Copy for arphdr
impl Copy for input_absinfo
[src]
impl Copy for input_absinfo
impl Copy for rlimit64
[src]
impl Copy for rlimit64
impl Copy for dirent
[src]
impl Copy for dirent
impl Copy for sockaddr_storage
[src]
impl Copy for sockaddr_storage
impl Copy for tm
[src]
impl Copy for tm
impl Copy for pthread_rwlock_t
[src]
impl Copy for pthread_rwlock_t
impl Copy for msghdr
[src]
impl Copy for msghdr
impl Copy for __timeval
[src]
impl Copy for __timeval
impl Copy for Elf32_Ehdr
[src]
impl Copy for Elf32_Ehdr
impl Copy for termios2
[src]
impl Copy for termios2
impl Copy for flock
[src]
impl Copy for flock
impl Copy for aiocb
[src]
impl Copy for aiocb
impl Copy for sockaddr_ll
[src]
impl Copy for sockaddr_ll
impl Copy for ff_constant_effect
[src]
impl Copy for ff_constant_effect
impl Copy for ff_trigger
[src]
impl Copy for ff_trigger
impl Copy for user_fpregs_struct
[src]
impl Copy for user_fpregs_struct
impl Copy for sysinfo
[src]
impl Copy for sysinfo
impl Copy for Elf32_Chdr
[src]
impl Copy for Elf32_Chdr
impl Copy for posix_spawnattr_t
[src]
impl Copy for posix_spawnattr_t
impl Copy for stat64
[src]
impl Copy for stat64
impl Copy for shmid_ds
[src]
impl Copy for shmid_ds
impl Copy for siginfo_t
[src]
impl Copy for siginfo_t
impl Copy for itimerval
[src]
impl Copy for itimerval
impl Copy for ff_rumble_effect
[src]
impl Copy for ff_rumble_effect
impl Copy for mq_attr
[src]
impl Copy for mq_attr
impl Copy for ipc_perm
[src]
impl Copy for ipc_perm
impl Copy for rlimit
[src]
impl Copy for rlimit
impl Copy for posix_spawn_file_actions_t
[src]
impl Copy for posix_spawn_file_actions_t
impl Copy for pthread_attr_t
[src]
impl Copy for pthread_attr_t
impl Copy for ff_condition_effect
[src]
impl Copy for ff_condition_effect
impl Copy for mcontext_t
[src]
impl Copy for mcontext_t
impl Copy for ucontext_t
[src]
impl Copy for ucontext_t
impl Copy for fd_set
[src]
impl Copy for fd_set
impl Copy for input_id
[src]
impl Copy for input_id
impl Copy for winsize
[src]
impl Copy for winsize
impl Copy for in_addr
[src]
impl Copy for in_addr
impl Copy for sockaddr_in6
[src]
impl Copy for sockaddr_in6
impl Copy for mmsghdr
[src]
impl Copy for mmsghdr
impl Copy for input_mask
[src]
impl Copy for input_mask
impl Copy for cmsghdr
[src]
impl Copy for cmsghdr
impl Copy for protoent
[src]
impl Copy for protoent
impl Copy for Elf64_Shdr
[src]
impl Copy for Elf64_Shdr
impl Copy for dl_phdr_info
[src]
impl Copy for dl_phdr_info
impl Copy for pthread_cond_t
[src]
impl Copy for pthread_cond_t
impl Copy for sigset_t
[src]
impl Copy for sigset_t
impl Copy for addrinfo
[src]
impl Copy for addrinfo
impl Copy for __exit_status
[src]
impl Copy for __exit_status
impl Copy for user
[src]
impl Copy for user
impl Copy for Dl_info
[src]
impl Copy for Dl_info
impl Copy for sigval
[src]
impl Copy for sigval
impl Copy for arpd_request
[src]
impl Copy for arpd_request
impl Copy for Elf32_Shdr
[src]
impl Copy for Elf32_Shdr
impl Copy for in6_addr
[src]
impl Copy for in6_addr
impl Copy for sockaddr
[src]
impl Copy for sockaddr
impl Copy for nlmsghdr
[src]
impl Copy for nlmsghdr
impl Copy for ff_effect
[src]
impl Copy for ff_effect
impl Copy for dqblk
[src]
impl Copy for dqblk
impl Copy for ipv6_mreq
[src]
impl Copy for ipv6_mreq
impl Copy for ip_mreq
[src]
impl Copy for ip_mreq
impl Copy for sembuf
[src]
impl Copy for sembuf
impl Copy for epoll_event
[src]
impl Copy for epoll_event
impl Copy for statvfs64
[src]
impl Copy for statvfs64
impl Copy for mallinfo
[src]
impl Copy for mallinfo
impl Copy for sigaction
[src]
impl Copy for sigaction
impl Copy for Elf64_Sym
[src]
impl Copy for Elf64_Sym
impl Copy for group
[src]
impl Copy for group
impl Copy for lconv
[src]
impl Copy for lconv
impl Copy for sem_t
[src]
impl Copy for sem_t
impl Copy for nl_mmap_hdr
[src]
impl Copy for nl_mmap_hdr
impl Copy for utsname
[src]
impl Copy for utsname
impl Copy for pthread_condattr_t
[src]
impl Copy for pthread_condattr_t
impl Copy for genlmsghdr
[src]
impl Copy for genlmsghdr
impl Copy for rusage
[src]
impl Copy for rusage
impl Copy for statfs
[src]
impl Copy for statfs
impl Copy for ff_periodic_effect
[src]
impl Copy for ff_periodic_effect
impl Copy for linger
[src]
impl Copy for linger
impl Copy for glob64_t
[src]
impl Copy for glob64_t
impl Copy for signalfd_siginfo
[src]
impl Copy for signalfd_siginfo
impl Copy for sockaddr_un
[src]
impl Copy for sockaddr_un
impl Copy for timeval
[src]
impl Copy for timeval
impl Copy for rtentry
[src]
impl Copy for rtentry
impl Copy for user_regs_struct
[src]
impl Copy for user_regs_struct
impl Copy for input_event
[src]
impl Copy for input_event
impl Copy for Elf64_Ehdr
[src]
impl Copy for Elf64_Ehdr
impl Copy for input_keymap_entry
[src]
impl Copy for input_keymap_entry
impl Copy for sockaddr_nl
[src]
impl Copy for sockaddr_nl
impl Copy for pthread_mutex_t
[src]
impl Copy for pthread_mutex_t
impl Copy for nlattr
[src]
impl Copy for nlattr
impl Copy for iovec
[src]
impl Copy for iovec
impl Copy for dirent64
[src]
impl Copy for dirent64
impl Copy for packet_mreq
[src]
impl Copy for packet_mreq
impl Copy for itimerspec
[src]
impl Copy for itimerspec
impl Copy for utmpx
[src]
impl Copy for utmpx
impl Copy for user_fpxregs_struct
[src]
impl Copy for user_fpxregs_struct
impl Copy for passwd
[src]
impl Copy for passwd
impl Copy for arpreq_old
[src]
impl Copy for arpreq_old
impl Copy for ff_ramp_effect
[src]
impl Copy for ff_ramp_effect
impl Copy for ff_envelope
[src]
impl Copy for ff_envelope
impl Copy for ff_replay
[src]
impl Copy for ff_replay
impl Copy for pollfd
[src]
impl Copy for pollfd
impl Copy for sched_param
[src]
impl Copy for sched_param
impl Copy for tms
[src]
impl Copy for tms
impl Copy for glob_t
[src]
impl Copy for glob_t
impl Copy for in6_rtmsg
[src]
impl Copy for in6_rtmsg
impl Copy for if_nameindex
[src]
impl Copy for if_nameindex
impl Copy for ucred
[src]
impl Copy for ucred
impl Copy for servent
[src]
impl Copy for servent
impl Copy for stat
[src]
impl Copy for stat
impl Copy for utimbuf
[src]
impl Copy for utimbuf
impl Copy for termios
[src]
impl Copy for termios
impl Copy for in6_pktinfo
[src]
impl Copy for in6_pktinfo
impl Copy for statfs64
[src]
impl Copy for statfs64
impl Copy for msqid_ds
[src]
impl Copy for msqid_ds
impl Copy for _libc_fpstate
[src]
impl Copy for _libc_fpstate
impl Copy for spwd
[src]
impl Copy for spwd
impl Copy for nlmsgerr
[src]
impl Copy for nlmsgerr
impl Copy for msginfo
[src]
impl Copy for msginfo
impl Copy for nl_mmap_req
[src]
impl Copy for nl_mmap_req
impl Copy for statvfs
[src]
impl Copy for statvfs
impl Copy for fsid_t
[src]
impl Copy for fsid_t
impl Copy for _Unwind_Reason_Code
impl Copy for _Unwind_Reason_Code
impl Copy for _Unwind_Action
Loading content...
impl Copy for _Unwind_Action
Implementors
impl Copy for WaitTimeoutResult
[src]
impl Copy for WaitTimeoutResult
impl Copy for System
[src]
impl Copy for System
impl Copy for SeekFrom
[src]
impl Copy for SeekFrom
impl Copy for ErrorKind
[src]
impl Copy for ErrorKind
impl Copy for RecvError
[src]
impl Copy for RecvError
impl Copy for ThreadId
[src]
impl Copy for ThreadId
impl Copy for Instant
[src]
impl Copy for Instant
impl Copy for TryRecvError
[src]
impl Copy for TryRecvError
impl Copy for SocketAddr
[src]
impl Copy for SocketAddr
impl Copy for FileType
[src]
impl Copy for FileType
impl Copy for IpAddr
[src]
impl Copy for IpAddr
impl Copy for SystemTime
[src]
impl Copy for SystemTime
impl Copy for Shutdown
[src]
impl Copy for Shutdown
impl Copy for ExitCode
[src]
impl Copy for ExitCode
impl Copy for ExitStatus
[src]
impl Copy for ExitStatus
impl Copy for RecvTimeoutError
[src]
impl Copy for RecvTimeoutError
impl Copy for TryFromIntError
[src]
impl Copy for TryFromIntError
impl Copy for TypeId
[src]
impl Copy for TypeId
impl Copy for RangeFull
[src]
impl Copy for RangeFull
impl Copy for NonZeroUsize
[src]
impl Copy for NonZeroUsize
impl Copy for PhantomPinned
[src]
impl Copy for PhantomPinned
impl Copy for Duration
[src]
impl Copy for Duration
impl Copy for SearchStep
[src]
impl Copy for SearchStep
impl Copy for boolean_enums::lstd::sync::atomic::Ordering
[src]
impl Copy for boolean_enums::lstd::sync::atomic::Ordering
impl Copy for Error
[src]
impl Copy for Error
impl Copy for UnicodeVersion
[src]
impl Copy for UnicodeVersion
impl Copy for boolean_enums::lstd::cmp::Ordering
[src]
impl Copy for boolean_enums::lstd::cmp::Ordering
impl Copy for Layout
[src]
impl Copy for Layout
impl Copy for TraitObject
[src]
impl Copy for TraitObject
impl Copy for NoneError
[src]
impl Copy for NoneError
impl Copy for CharTryFromError
[src]
impl Copy for CharTryFromError
impl Copy for FpCategory
[src]
impl Copy for FpCategory
impl Copy for Global
[src]
impl Copy for Global
impl Copy for ParseError
[src]
impl Copy for ParseError
impl Copy for Ipv6MulticastScope
[src]
impl Copy for Ipv6MulticastScope
impl Copy for CpuidResult
[src]
impl Copy for CpuidResult
impl Copy for __m128
[src]
impl Copy for __m128
impl Copy for __m128d
[src]
impl Copy for __m128d
impl Copy for __m128i
[src]
impl Copy for __m128i
impl Copy for __m256
[src]
impl Copy for __m256
impl Copy for __m256d
[src]
impl Copy for __m256d
impl Copy for __m256i
[src]
impl Copy for __m256i
impl Copy for __m512
[src]
impl Copy for __m512
impl Copy for __m512d
[src]
impl Copy for __m512d
impl Copy for __m512i
[src]
impl Copy for __m512i
impl Copy for __m64
[src]
impl Copy for __m64
impl Copy for Ipv4Addr
[src]
impl Copy for Ipv4Addr
impl Copy for Ipv6Addr
[src]
impl Copy for Ipv6Addr
impl Copy for SocketAddrV4
[src]
impl Copy for SocketAddrV4
impl Copy for SocketAddrV6
[src]
impl Copy for SocketAddrV6
impl Copy for NonZeroU128
[src]
impl Copy for NonZeroU128
impl Copy for NonZeroU16
[src]
impl Copy for NonZeroU16
impl Copy for NonZeroU32
[src]
impl Copy for NonZeroU32
impl Copy for NonZeroU64
[src]
impl Copy for NonZeroU64
impl Copy for NonZeroU8
[src]
impl Copy for NonZeroU8
impl Copy for Utf8Error
[src]
impl Copy for Utf8Error
impl<'a> Copy for Ancestors<'a>
[src]
impl<'a> Copy for Ancestors<'a>
impl<'a> Copy for Prefix<'a>
[src]
impl<'a> Copy for Prefix<'a>
impl<'a> Copy for Component<'a>
[src]
impl<'a> Copy for Component<'a>
impl<'a> Copy for PrefixComponent<'a>
[src]
impl<'a> Copy for PrefixComponent<'a>
impl<'a> Copy for Arguments<'a>
[src]
impl<'a> Copy for Arguments<'a>
impl<F> Copy for RepeatWith<F> where
F: Copy,
[src]
impl<F> Copy for RepeatWith<F> where
F: Copy,
impl<Idx> Copy for RangeTo<Idx> where
Idx: Copy,
[src]
impl<Idx> Copy for RangeTo<Idx> where
Idx: Copy,
impl<Idx> Copy for RangeToInclusive<Idx> where
Idx: Copy,
[src]
impl<Idx> Copy for RangeToInclusive<Idx> where
Idx: Copy,
impl<P> Copy for Pin<P> where
P: Copy,
[src]
impl<P> Copy for Pin<P> where
P: Copy,
impl<T> Copy for Discriminant<T>
[src]
impl<T> Copy for Discriminant<T>
impl<T> Copy for Bound<T> where
T: Copy,
[src]
impl<T> Copy for Bound<T> where
T: Copy,
impl<T> Copy for Option<T> where
T: Copy,
[src]
impl<T> Copy for Option<T> where
T: Copy,
impl<T> Copy for TrySendError<T> where
T: Copy,
[src]
impl<T> Copy for TrySendError<T> where
T: Copy,
impl<T> Copy for Poll<T> where
T: Copy,
[src]
impl<T> Copy for Poll<T> where
T: Copy,
impl<T> Copy for Reverse<T> where
T: Copy,
[src]
impl<T> Copy for Reverse<T> where
T: Copy,
impl<T> Copy for PhantomData<T> where
T: ?Sized,
[src]
impl<T> Copy for PhantomData<T> where
T: ?Sized,
impl<T> Copy for ManuallyDrop<T> where
T: Copy + ?Sized,
[src]
impl<T> Copy for ManuallyDrop<T> where
T: Copy + ?Sized,
impl<T> Copy for Wrapping<T> where
T: Copy,
[src]
impl<T> Copy for Wrapping<T> where
T: Copy,
impl<T> Copy for NonNull<T> where
T: ?Sized,
[src]
impl<T> Copy for NonNull<T> where
T: ?Sized,
impl<T> Copy for SendError<T> where
T: Copy,
[src]
impl<T> Copy for SendError<T> where
T: Copy,
impl<T, E> Copy for Result<T, E> where
E: Copy,
T: Copy,
[src]
impl<T, E> Copy for Result<T, E> where
E: Copy,
T: Copy,
impl<Y, R> Copy for GeneratorState<Y, R> where
R: Copy,
Y: Copy,
[src]
impl<Y, R> Copy for GeneratorState<Y, R> where
R: Copy,
Y: Copy,