pub trait Default {
const fn default() -> Self;
}
Expand description
A trait for giving a type a useful default value.
Sometimes, you want to fall back to some kind of default value, and
don’t particularly care what it is. This comes up often with struct
s
that define a set of options:
struct SomeOptions {
foo: i32,
bar: f32,
}
How can we define some default values? You can use Default
:
#[derive(Default)]
struct SomeOptions {
foo: i32,
bar: f32,
}
fn main() {
let options: SomeOptions = Default::default();
}
Now, you get all of the default values. Rust implements Default
for various primitives types.
If you want to override a particular option, but still retain the other defaults:
fn main() {
let options = SomeOptions { foo: 42, ..Default::default() };
}
Derivable
This trait can be used with #[derive]
if all of the type’s fields implement
Default
. When derive
d, it will use the default value for each field’s type.
enum
s
When using #[derive(Default)]
on an enum
, you need to choose which unit variant will be
default. You do this by placing the #[default]
attribute on the variant.
#[derive(Default)]
enum Kind {
#[default]
A,
B,
C,
}
You cannot use the #[default]
attribute on non-unit or non-exhaustive variants.
How can I implement Default
?
Provide an implementation for the default()
method that returns the value of
your type that should be the default:
enum Kind {
A,
B,
C,
}
impl Default for Kind {
fn default() -> Self { Kind::A }
}
Examples
#[derive(Default)]
struct SomeOptions {
foo: i32,
bar: f32,
}
Required Methods
sourceconst fn default() -> Self
const fn default() -> Self
Returns the “default value” for a type.
Default values are often some kind of initial value, identity value, or anything else that may make sense as a default.
Examples
Using built-in default values:
let i: i8 = Default::default();
let (x, y): (Option<String>, f64) = Default::default();
let (a, b, (c, d)): (i32, u32, (bool, bool)) = Default::default();
Making your own:
enum Kind {
A,
B,
C,
}
impl Default for Kind {
fn default() -> Self { Kind::A }
}
Implementors
impl Default for &str
impl Default for &CStr
impl Default for &OsStr
impl Default for &mut str
impl Default for MapAddr
impl Default for FutexClockId
impl Default for FutexOp
impl Default for PageType
impl Default for Feature
impl Default for Version
impl Default for ExceptionType
impl Default for ExceptionVector
impl Default for HandleResult
impl Default for PceError
impl Default for QcnlError
impl Default for Quote3Error
impl Default for SgxStatus
impl Default for DirIndex
impl Default for EcResult
impl Default for RsaKeyType
impl Default for RsaResult
impl Default for PckCertFlag
impl Default for ProdType
impl Default for QeType
impl Default for QlAttestationAlgorithmId
impl Default for QlCertKeyType
impl Default for QlConfigVersion
impl Default for QlLogLevel
impl Default for QlPathType
impl Default for QlQvResult
impl Default for QlRequestPolicy
impl Default for QvPathType
impl Default for DhSessionRole
impl Default for EnclaveMode
impl Default for KeyName
impl Default for ProtectPerm
impl Default for RaKeyType
impl Default for QuoteSignType
impl Default for SwitchlessWokerEvent
impl Default for SwitchlessWokerType
impl Default for SgxDeviceStatus
impl Default for TcsPolicy
impl Default for bool
impl Default for char
impl Default for f32
impl Default for f64
impl Default for i8
impl Default for i16
impl Default for i32
impl Default for i64
impl Default for i128
impl Default for isize
impl Default for u8
impl Default for u16
impl Default for u32
impl Default for u64
impl Default for u128
impl Default for ()
impl Default for usize
impl Default for AlignReq
impl Default for CpuidResult
impl Default for AddrInfoHints
impl Default for MsgHdrFlags
impl Default for sgx_sync::condvar::Condvar
impl Default for FutexFlags
impl Default for MovableMutex
impl Default for MovableRwLock
impl Default for PageFlags
impl Default for PageInfo
impl Default for Rng
impl Default for AlignKeyRequest
impl Default for AlignReport2Mac
impl Default for AlignReport
impl Default for AlignReportData
impl Default for AlignTargetInfo
impl Default for CpuContext
impl Default for ExceptionInfo
impl Default for CssBody
impl Default for CssBuffer
impl Default for CssHeader
impl Default for CssKey
impl Default for DataDir
impl Default for MetaData
impl Default for AlignEc256PrivateKey
impl Default for AlignKey128bit
impl Default for AlignKey256bit
impl Default for AlignMac128bit
impl Default for AlignMac256bit
impl Default for Ec256PrivateKey
impl Default for Ec256PublicKey
impl Default for Ec256Signature
impl Default for Rsa2048Key
impl Default for Rsa2048Param
impl Default for Rsa2048PrivKey
impl Default for Rsa2048PubKey
impl Default for Rsa2048Signature
impl Default for Rsa3072Key
impl Default for Rsa3072Param
impl Default for Rsa3072PrivKey
impl Default for Rsa3072PubKey
impl Default for Rsa3072Signature
impl Default for Sha1Hash
impl Default for Sha256Hash
impl Default for Sha384Hash
impl Default for Sm3Hash
impl Default for PceInfo
impl Default for QlAuthData
impl Default for QlCertificationData
impl Default for QlEcdsaSigData
impl Default for QlPPIDRsa3072EncryptedCertInfo
impl Default for QlQe3Id
impl Default for QlQeReportInfo
impl Default for QlQvSupplemental
impl Default for QlQveCollateralParam
impl Default for Quote3
impl Default for QuoteHeader
impl Default for CDhMsg1
impl Default for CDhMsg2
impl Default for CDhMsg3
impl Default for CDhMsg3Body
impl Default for CDhSession
impl Default for CEnclaveIdentity
impl Default for CRaMsg1
impl Default for CRaMsg2
impl Default for CRaMsg3
impl Default for PsSecPropDesc
impl Default for AttKeyId
impl Default for AttKeyIdExt
impl Default for BaseName
impl Default for PlatformInfo
impl Default for QeReportInfo
impl Default for QlAttKeyId
impl Default for Quote
impl Default for QuoteNonce
impl Default for Spid
impl Default for UpdateInfoBit
impl Default for CDcapMRaMsg2
impl Default for CDcapRaMsg1
impl Default for CDcapRaMsg3
impl Default for CDcapURaMsg2
impl Default for EnclaveIdentity
impl Default for timespec
impl Default for Report2
impl Default for Report2Mac
impl Default for TeeAttributes
impl Default for TeeCpuSvn
impl Default for TeeMeasurement
impl Default for TeeReportData
impl Default for TeeReportType
impl Default for CAesGcmData
impl Default for CSealedData
impl Default for Attributes
impl Default for AttributesFlags
impl Default for ConfigId
impl Default for CpuSvn
impl Default for KeyId
impl Default for KeyPolicy
impl Default for KeyRequest
impl Default for Measurement
impl Default for MiscAttribute
impl Default for MiscSelect
impl Default for Report
impl Default for ReportBody
impl Default for ReportData
impl Default for TargetInfo
impl Default for SwitchlessConfig
impl Default for SwitchlessWokerStats
impl Default for EcdsaSigDataV4
impl Default for QeReportCertificationData
impl Default for Quote4
impl Default for Quote4Header
impl Default for Report2Body
impl Default for TeeInfo
impl Default for TeeTcbInfo
impl Default for TeeTcbSvn
impl Default for KssConfig
impl Default for Global
impl Default for Box<str, Global>
impl Default for Box<CStr, Global>
impl Default for Box<OsStr>
impl Default for DefaultHasher
impl Default for RandomState
impl Default for CString
impl Default for OsString
impl Default for Error
impl Default for SipHasher
impl Default for sgx_tstd::io::Empty
impl Default for Sink
impl Default for PhantomPinned
impl Default for RangeFull
impl Default for PathBuf
impl Default for String
impl Default for AtomicBool
impl Default for AtomicI8
impl Default for AtomicI16
impl Default for AtomicI32
impl Default for AtomicI64
impl Default for AtomicIsize
impl Default for AtomicU8
impl Default for AtomicU16
impl Default for AtomicU32
impl Default for AtomicU64
impl Default for AtomicUsize
impl Default for sgx_tstd::sync::Condvar
impl Default for Duration
impl Default for FileTimes
impl<B> Default for Cow<'_, B>where
B: ToOwned + ?Sized,
<B as ToOwned>::Owned: Default,
impl<H> Default for BuildHasherDefault<H>
impl<Idx> Default for Range<Idx>where
Idx: Default,
impl<K, V> Default for BTreeMap<K, V, Global>
impl<K, V, S> Default for sgx_tstd::collections::hash_map::HashMap<K, V, S>where
S: Default,
impl<K, V, S, A> Default for hashbrown_tstd::map::HashMap<K, V, S, A>where
S: Default,
A: Default + Allocator + Clone,
impl<T> Default for &[T]
impl<T> Default for &mut [T]
impl<T> Default for Option<T>
impl<T> Default for [T; 0]
impl<T> Default for [T; 1]where
T: Default,
impl<T> Default for [T; 2]where
T: Default,
impl<T> Default for [T; 3]where
T: Default,
impl<T> Default for [T; 4]where
T: Default,
impl<T> Default for [T; 5]where
T: Default,
impl<T> Default for [T; 6]where
T: Default,
impl<T> Default for [T; 7]where
T: Default,
impl<T> Default for [T; 8]where
T: Default,
impl<T> Default for [T; 9]where
T: Default,
impl<T> Default for [T; 10]where
T: Default,
impl<T> Default for [T; 11]where
T: Default,
impl<T> Default for [T; 12]where
T: Default,
impl<T> Default for [T; 13]where
T: Default,
impl<T> Default for [T; 14]where
T: Default,
impl<T> Default for [T; 15]where
T: Default,
impl<T> Default for [T; 16]where
T: Default,
impl<T> Default for [T; 17]where
T: Default,
impl<T> Default for [T; 18]where
T: Default,
impl<T> Default for [T; 19]where
T: Default,
impl<T> Default for [T; 20]where
T: Default,
impl<T> Default for [T; 21]where
T: Default,
impl<T> Default for [T; 22]where
T: Default,
impl<T> Default for [T; 23]where
T: Default,
impl<T> Default for [T; 24]where
T: Default,
impl<T> Default for [T; 25]where
T: Default,
impl<T> Default for [T; 26]where
T: Default,
impl<T> Default for [T; 27]where
T: Default,
impl<T> Default for [T; 28]where
T: Default,
impl<T> Default for [T; 29]where
T: Default,
impl<T> Default for [T; 30]where
T: Default,
impl<T> Default for [T; 31]where
T: Default,
impl<T> Default for [T; 32]where
T: Default,
impl<T> Default for (T₁, T₂, …, Tₙ)where
T: Default,
This trait is implemented for tuples up to twelve items long.