1.0.0[][src]Trait sgx_tstd::marker::Copy

#[lang = "copy"]pub trait Copy: Clone { }

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:

Implementations on Foreign Types

impl Copy for CpuidResult[src]

impl Copy for __m512i[src]

impl Copy for __m256i[src]

impl Copy for __m64[src]

impl Copy for __m256[src]

impl Copy for __m512d[src]

impl Copy for __m512[src]

impl Copy for __m128[src]

impl Copy for __m128i[src]

impl Copy for __m256d[src]

impl Copy for __m128d[src]

impl Copy for _Unwind_Action[src]

impl Copy for _Unwind_Reason_Code[src]

impl Copy for AlignReq[src]

impl Copy for sgx_rsa3072_public_key_t[src]

impl Copy for sgx_align_ec256_dh_shared_t[src]

impl Copy for sgx_kss_config_t[src]

impl Copy for sgx_dh_session_enclave_identity_t[src]

impl Copy for layout_entry_t[src]

impl Copy for sgx_report_data_t[src]

impl Copy for sgx_ql_ecdsa_sig_data_t[src]

impl Copy for sgx_rsa3072_signature_t[src]

impl Copy for sgx_dh_msg2_t[src]

impl Copy for sgx_rsa_key_type_t[src]

impl Copy for sgx_basename_t[src]

impl Copy for sgx_att_key_id_t[src]

impl Copy for sgx_exception_info_t[src]

impl Copy for sgx_attributes_t[src]

impl Copy for sgx_exception_vector_t[src]

impl Copy for sgx_quote3_error_t[src]

impl Copy for sgx_thread_mutex_attr_t[src]

impl Copy for rsa_params_t[src]

impl Copy for sgx_rsa_result_t[src]

impl Copy for sgx_platform_info_t[src]

impl Copy for sgx_pce_error_t[src]

impl Copy for sgx_cpu_context_t[src]

impl Copy for sgx_generic_ecresult_t[src]

impl Copy for sgx_misc_attribute_t[src]

impl Copy for sgx_ra_msg1_t[src]

impl Copy for sgx_align_mac_128bit_t[src]

impl Copy for sgx_ql_path_type_t[src]

impl Copy for sgx_ql_qe3_id_t[src]

impl Copy for sgx_dh_msg3_t[src]

impl Copy for sgx_ec256_dh_shared_t[src]

impl Copy for sgx_ps_cap_t[src]

impl Copy for sgx_quote_sign_type_t[src]

impl Copy for sgx_align_ec256_private_t[src]

impl Copy for sgx_update_info_bit_t[src]

impl Copy for data_directory_t[src]

impl Copy for sgx_dh_msg1_t[src]

impl Copy for sgx_ps_sec_prop_desc_t[src]

impl Copy for sgx_pce_info_t[src]

impl Copy for sgx_ql_att_key_id_t[src]

impl Copy for sgx_thread_cond_attr_t[src]

impl Copy for dir_index_t[src]

impl Copy for ecc_param_t[src]

impl Copy for sgx_qe_report_info_t[src]

impl Copy for align_req_t[src]

impl Copy for sgx_rsa3072_key_t[src]

impl Copy for sgx_ql_certification_data_t[src]

impl Copy for sgx_ql_attestation_algorithm_id_t[src]

impl Copy for sgx_target_info_t[src]

impl Copy for sgx_quote_nonce_t[src]

impl Copy for sgx_ec256_public_t[src]

impl Copy for sgx_ql_qe_report_info_t[src]

impl Copy for sgx_uswitchless_worker_stats_t[src]

impl Copy for sgx_ec256_signature_t[src]

impl Copy for sgx_ql_auth_data_t[src]

impl Copy for sgx_ql_config_version_t[src]

impl Copy for layout_group_t[src]

impl Copy for sgx_key_id_t[src]

impl Copy for sgx_ra_key_type_t[src]

impl Copy for sgx_aes_gcm_data_t[src]

impl Copy for sgx_dh_session_role_t[src]

impl Copy for sgx_ql_request_policy_t[src]

impl Copy for sgx_ra_msg2_t[src]

impl Copy for sgx_dh_session_t[src]

impl Copy for sgx_uswitchless_worker_event_t[src]

impl Copy for sgx_ra_msg3_t[src]

impl Copy for sgx_exception_type_t[src]

impl Copy for sgx_report_t[src]

impl Copy for sgx_quote_header_t[src]

impl Copy for sgx_key_request_t[src]

impl Copy for sgx_quote_t[src]

impl Copy for sgx_uswitchless_worker_type_t[src]

impl Copy for sgx_ec256_private_t[src]

impl Copy for sgx_spid_t[src]

impl Copy for sgx_align_key_256bit_t[src]

impl Copy for sgx_ql_ppid_rsa3072_encrypted_cert_info_t[src]

impl Copy for sgx_sealed_data_t[src]

impl Copy for sgx_ql_cert_key_type_t[src]

impl Copy for sgx_cpu_svn_t[src]

impl Copy for sgx_align_key_128bit_t[src]

impl Copy for sgx_align_mac_256bit_t[src]

impl Copy for sgx_att_key_id_ext_t[src]

impl Copy for sgx_status_t[src]

impl Copy for sgx_ql_qv_supplemental_t[src]

impl Copy for sgx_quote3_t[src]

impl Copy for sgx_dh_msg3_body_t[src]

impl Copy for sgx_ql_qv_result_t[src]

impl Copy for sgx_qcnl_error_t[src]

impl Copy for sgx_report_body_t[src]

impl Copy for sgx_measurement_t[src]

impl Copy for sgx_device_status_t[src]

impl Copy for sgx_qv_path_type_t[src]

impl Copy for SgxGlobalData[src]

impl Copy for Feature[src]

impl Copy for SgxThreadData[src]

impl Copy for ucred[src]

impl Copy for addrinfo[src]

impl Copy for sigval[src]

impl Copy for tm[src]

impl Copy for in_addr[src]

impl Copy for sockaddr_in[src]

impl Copy for msghdr[src]

impl Copy for DIR[src]

impl Copy for sigset_t[src]

impl Copy for sockaddr_ll[src]

impl Copy for iovec[src]

impl Copy for sockaddr_un[src]

impl Copy for sockaddr_in6[src]

impl Copy for ip_mreq[src]

impl Copy for sockaddr_nl[src]

impl Copy for cpu_set_t[src]

impl Copy for passwd[src]

impl Copy for timespec[src]

impl Copy for winsize[src]

impl Copy for linger[src]

impl Copy for sockaddr_storage[src]

impl Copy for stat64[src]

impl Copy for sockaddr[src]

impl Copy for in6_addr[src]

impl Copy for timeval[src]

impl Copy for epoll_event[src]

impl Copy for dirent64[src]

impl Copy for pthread_once_t[src]

impl Copy for sigaction[src]

impl Copy for dirent[src]

impl Copy for stat[src]

impl Copy for hostent[src]

impl Copy for fd_set[src]

impl Copy for pollfd[src]

impl Copy for siginfo_t[src]

impl Copy for cmsghdr[src]

impl Copy for ipv6_mreq[src]

impl Copy for SeekFrom[src]

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Implementors

impl Copy for ![src]

impl Copy for AllocInit[src]

impl Copy for ReallocPlacement[src]

impl Copy for sgx_tstd::cmp::Ordering[src]

impl Copy for Infallible[src]

impl Copy for SgxThreadPolicy[src]

impl Copy for ErrorKind[src]

impl Copy for sgx_tstd::io::SeekFrom[src]

impl Copy for IpAddr[src]

impl Copy for Ipv6MulticastScope[src]

impl Copy for Shutdown[src]

impl Copy for SocketAddr[src]

impl Copy for FpCategory[src]

impl Copy for SearchStep[src]

impl Copy for sgx_tstd::sync::atomic::Ordering[src]

impl Copy for Global[src]

impl Copy for Layout[src]

impl Copy for MemoryBlock[src]

impl Copy for TypeId[src]

impl Copy for TryFromSliceError[src]

impl Copy for CharTryFromError[src]

impl Copy for UnicodeVersion[src]

impl Copy for Error[src]

impl Copy for PhantomPinned[src]

impl Copy for Ipv4Addr[src]

impl Copy for Ipv6Addr[src]

impl Copy for SocketAddrV4[src]

impl Copy for SocketAddrV6[src]

impl Copy for NonZeroI128[src]

impl Copy for NonZeroI16[src]

impl Copy for NonZeroI32[src]

impl Copy for NonZeroI64[src]

impl Copy for NonZeroI8[src]

impl Copy for NonZeroIsize[src]

impl Copy for NonZeroU128[src]

impl Copy for NonZeroU16[src]

impl Copy for NonZeroU32[src]

impl Copy for NonZeroU64[src]

impl Copy for NonZeroU8[src]

impl Copy for NonZeroUsize[src]

impl Copy for TryFromIntError[src]

impl Copy for RangeFull[src]

impl Copy for NoneError[src]

impl Copy for TraitObject[src]

impl Copy for Utf8Error[src]

impl Copy for WaitTimeoutResult[src]

impl Copy for RawWakerVTable[src]

impl Copy for ThreadId[src]

impl Copy for Duration[src]

impl Copy for Instant[src]

impl Copy for SystemTime[src]

impl Copy for FileType[src]

impl Copy for bool[src]

impl Copy for char[src]

impl Copy for f32[src]

impl Copy for f64[src]

impl Copy for i8[src]

impl Copy for i16[src]

impl Copy for i32[src]

impl Copy for i64[src]

impl Copy for i128[src]

impl Copy for isize[src]

impl Copy for u8[src]

impl Copy for u16[src]

impl Copy for u32[src]

impl Copy for u64[src]

impl Copy for u128[src]

impl Copy for usize[src]

impl<'_, T> Copy for &'_ T where
    T: ?Sized
[src]

Shared references can be copied, but mutable references cannot!

impl<'a> Copy for Component<'a>[src]

impl<'a> Copy for Prefix<'a>[src]

impl<'a> Copy for ErrorIter<'a>[src]

impl<'a> Copy for Arguments<'a>[src]

impl<'a> Copy for IoSlice<'a>[src]

impl<'a> Copy for Ancestors<'a>[src]

impl<'a> Copy for PrefixComponent<'a>[src]

impl<F> Copy for RepeatWith<F> where
    F: Copy
[src]

impl<Idx> Copy for RangeTo<Idx> where
    Idx: Copy
[src]

impl<Idx> Copy for RangeToInclusive<Idx> where
    Idx: Copy
[src]

impl<P> Copy for Pin<P> where
    P: Copy
[src]

impl<T> Copy for *const T where
    T: ?Sized
[src]

impl<T> Copy for *mut T where
    T: ?Sized
[src]

impl<T> Copy for Bound<T> where
    T: Copy
[src]

impl<T> Copy for Option<T> where
    T: Copy
[src]

impl<T> Copy for Poll<T> where
    T: Copy
[src]

impl<T> Copy for Reverse<T> where
    T: Copy
[src]

impl<T> Copy for PhantomData<T> where
    T: ?Sized
[src]

impl<T> Copy for Discriminant<T>[src]

impl<T> Copy for ManuallyDrop<T> where
    T: Copy + ?Sized
[src]

impl<T> Copy for Wrapping<T> where
    T: Copy
[src]

impl<T> Copy for NonNull<T> where
    T: ?Sized
[src]

impl<T> Copy for MaybeUninit<T> where
    T: Copy
[src]

impl<T, E> Copy for Result<T, E> where
    E: Copy,
    T: Copy
[src]

impl<Y, R> Copy for GeneratorState<Y, R> where
    R: Copy,
    Y: Copy
[src]

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