--- title: SendableMetatype framework: swift role: symbol role_heading: Protocol path: swift/sendablemetatype --- # SendableMetatype A type whose metatype can be shared across arbitrary isolation domains without introducing a risk of data races. ## Declaration ```swift protocol SendableMetatype : ~Copyable, ~Escapable ``` ## Overview Overview When a generic type T conforms to SendableMetatype, its metatype T.Type conforms to Sendable. All concrete types implicitly conform to the SendableMetatype protocol, so its primary purpose is in generic code to prohibit the use of isolated conformances along with the generic type. A generic type T will need a SendableMetatype conformance when its metatype is shared across concurrency boundaries. For example, protocol P { static func f() } func useFromAnotherTask(_: T.Type) { Task { @concurrent in T.f() // error: capturing non-Sendable type `T.Type` in a concurrently-executing task } } The potential data race above would occur when useFromAnotherTask is provided with an isolated conformance to P. For example: @MainActor class MyModel: @MainActor P { /* implicitly @MainActor */ static func f() { /* on the main actor */ } } useFromAnotherTask(MyModel.self) Here, the error within the body of useFromAnotherTask is preventing the isolated conformance from leaving the current task and actor. The signature of useFromAnotherTask can be adjusted to introduce a requirement on SendableMetatype: func useFromAnotherTask(_: T.Type) { Task { @concurrent in T.f() // error: okay, T.Type is Sendable } } useFromAnotherTask(MyModel.self) // error: cannot use main-actor-isolated conformance `MyModel: P` for a `SendableMetatype`-conforming type parameter `T` The Sendable protocol inherits from SendableMetatype, so any generic type T with a requirement T: Sendable will have the implied requirement T: SendableMetatype. ## Relationships ### Inherited By - [Actor](swift/actor.md) - [Clock](swift/clock.md) - [CodingKey](swift/codingkey.md) - [DistributedActor](distributed/distributedactor.md) - [DistributedActorSystem](distributed/distributedactorsystem.md) - [DistributedActorSystemError](distributed/distributedactorsystemerror.md) - [DurationProtocol](swift/durationprotocol.md) - [Error](swift/error.md) - [Executor](swift/executor.md) - [InstantProtocol](swift/instantprotocol.md) - [Sendable](swift/sendable.md) - [SerialExecutor](swift/serialexecutor.md) - [TaskExecutor](swift/taskexecutor.md) - [UnsafeSendable](swift/unsafesendable.md) ### Conforming Types - [Array](swift/array.md) - [ArraySlice](swift/arrayslice.md) - [AsyncCompactMapSequence](swift/asynccompactmapsequence.md) - [AsyncCompactMapSequence.Iterator](swift/asynccompactmapsequence/iterator.md) - [AsyncDropFirstSequence](swift/asyncdropfirstsequence.md) - [AsyncDropFirstSequence.Iterator](swift/asyncdropfirstsequence/iterator.md) - [AsyncDropWhileSequence](swift/asyncdropwhilesequence.md) - [AsyncDropWhileSequence.Iterator](swift/asyncdropwhilesequence/iterator.md) - [AsyncFilterSequence](swift/asyncfiltersequence.md) - [AsyncFilterSequence.Iterator](swift/asyncfiltersequence/iterator.md) - [AsyncFlatMapSequence](swift/asyncflatmapsequence.md) - [AsyncFlatMapSequence.Iterator](swift/asyncflatmapsequence/iterator.md) - [AsyncMapSequence](swift/asyncmapsequence.md) - [AsyncMapSequence.Iterator](swift/asyncmapsequence/iterator.md) - [AsyncPrefixSequence](swift/asyncprefixsequence.md) - [AsyncPrefixSequence.Iterator](swift/asyncprefixsequence/iterator.md) - [AsyncPrefixWhileSequence](swift/asyncprefixwhilesequence.md) - [AsyncPrefixWhileSequence.Iterator](swift/asyncprefixwhilesequence/iterator.md) - [AsyncStream](swift/asyncstream.md) - [AsyncStream.Continuation](swift/asyncstream/continuation.md) - [AsyncStream.Continuation.BufferingPolicy](swift/asyncstream/continuation/bufferingpolicy.md) - [AsyncStream.Continuation.Termination](swift/asyncstream/continuation/termination.md) - [AsyncStream.Continuation.YieldResult](swift/asyncstream/continuation/yieldresult.md) - [AsyncThrowingCompactMapSequence](swift/asyncthrowingcompactmapsequence.md) - [AsyncThrowingCompactMapSequence.Iterator](swift/asyncthrowingcompactmapsequence/iterator.md) - [AsyncThrowingDropWhileSequence](swift/asyncthrowingdropwhilesequence.md) - [AsyncThrowingDropWhileSequence.Iterator](swift/asyncthrowingdropwhilesequence/iterator.md) - [AsyncThrowingFilterSequence](swift/asyncthrowingfiltersequence.md) - [AsyncThrowingFilterSequence.Iterator](swift/asyncthrowingfiltersequence/iterator.md) - [AsyncThrowingFlatMapSequence](swift/asyncthrowingflatmapsequence.md) - [AsyncThrowingFlatMapSequence.Iterator](swift/asyncthrowingflatmapsequence/iterator.md) - [AsyncThrowingMapSequence](swift/asyncthrowingmapsequence.md) - [AsyncThrowingMapSequence.Iterator](swift/asyncthrowingmapsequence/iterator.md) - [AsyncThrowingPrefixWhileSequence](swift/asyncthrowingprefixwhilesequence.md) - [AsyncThrowingPrefixWhileSequence.Iterator](swift/asyncthrowingprefixwhilesequence/iterator.md) - [AsyncThrowingStream](swift/asyncthrowingstream.md) - [AsyncThrowingStream.Continuation](swift/asyncthrowingstream/continuation.md) - [AsyncThrowingStream.Continuation.BufferingPolicy](swift/asyncthrowingstream/continuation/bufferingpolicy.md) - [AsyncThrowingStream.Continuation.Termination](swift/asyncthrowingstream/continuation/termination.md) - [AsyncThrowingStream.Continuation.YieldResult](swift/asyncthrowingstream/continuation/yieldresult.md) - [Atomic](synchronization/atomic.md) - [AtomicLazyReference](synchronization/atomiclazyreference.md) - [AtomicLoadOrdering](synchronization/atomicloadordering.md) - [AtomicStoreOrdering](synchronization/atomicstoreordering.md) - [AtomicUpdateOrdering](synchronization/atomicupdateordering.md) - [Bool](swift/bool.md) - [CancellationError](swift/cancellationerror.md) - [Character](swift/character.md) - [CheckedContinuation](swift/checkedcontinuation.md) - [ClosedRange](swift/closedrange.md) - [ClosedRange.Index](swift/closedrange/index.md) - [CodingUserInfoKey](swift/codinguserinfokey.md) - [CollectionDifference](swift/collectiondifference.md) - [CollectionDifference.Change](swift/collectiondifference/change.md) - [CollectionDifference.Index](swift/collectiondifference/index.md) - [CollectionOfOne](swift/collectionofone.md) - [CollectionOfOne.Iterator](swift/collectionofone/iterator.md) - [CommandLine](swift/commandline.md) - [ContiguousArray](swift/contiguousarray.md) - [ContinuousClock](swift/continuousclock.md) - [ContinuousClock.Instant](swift/continuousclock/instant.md) - [DecodingError](swift/decodingerror.md) - [DecodingError.Context](swift/decodingerror/context.md) - [DefaultIndices](swift/defaultindices.md) - [DefaultStringInterpolation](swift/defaultstringinterpolation.md) - [Dictionary](swift/dictionary.md) - [Dictionary.Index](swift/dictionary/index.md) - [Dictionary.Iterator](swift/dictionary/iterator.md) - [Dictionary.Keys](swift/dictionary/keys-swift.struct.md) - [Dictionary.Keys.Iterator](swift/dictionary/keys-swift.struct/iterator.md) - [Dictionary.Values](swift/dictionary/values-swift.struct.md) - [Dictionary.Values.Iterator](swift/dictionary/values-swift.struct/iterator.md) - [DiscontiguousSlice](swift/discontiguousslice.md) - [DiscontiguousSlice.Index](swift/discontiguousslice/index.md) - [DistributedActorCodingError](distributed/distributedactorcodingerror.md) - [Double](swift/double.md) - [Double.SIMD16Storage](swift/double/simd16storage.md) - [Double.SIMD2Storage](swift/double/simd2storage.md) - [Double.SIMD32Storage](swift/double/simd32storage.md) - [Double.SIMD4Storage](swift/double/simd4storage.md) - [Double.SIMD64Storage](swift/double/simd64storage.md) - [Double.SIMD8Storage](swift/double/simd8storage.md) - [DropFirstSequence](swift/dropfirstsequence.md) - [DropWhileSequence](swift/dropwhilesequence.md) - [DropWhileSequence.Iterator](swift/dropwhilesequence/iterator.md) - [Duration](swift/duration.md) - [Duration.TimeFormatStyle](swift/duration/timeformatstyle.md) - [Duration.TimeFormatStyle.Attributed](swift/duration/timeformatstyle/attributed-swift.struct.md) - [Duration.TimeFormatStyle.Pattern](swift/duration/timeformatstyle/pattern-swift.struct.md) - [Duration.UnitsFormatStyle](swift/duration/unitsformatstyle.md) - [Duration.UnitsFormatStyle.Attributed](swift/duration/unitsformatstyle/attributed-swift.struct.md) - [Duration.UnitsFormatStyle.FractionalPartDisplayStrategy](swift/duration/unitsformatstyle/fractionalpartdisplaystrategy.md) - [Duration.UnitsFormatStyle.Unit](swift/duration/unitsformatstyle/unit.md) - [Duration.UnitsFormatStyle.UnitWidth](swift/duration/unitsformatstyle/unitwidth-swift.struct.md) - [Duration.UnitsFormatStyle.ZeroValueUnitsDisplayStrategy](swift/duration/unitsformatstyle/zerovalueunitsdisplaystrategy.md) - [EmptyCollection](swift/emptycollection.md) - [EmptyCollection.Iterator](swift/emptycollection/iterator.md) - [EncodingError](swift/encodingerror.md) - [EncodingError.Context](swift/encodingerror/context.md) - [EnumeratedSequence](swift/enumeratedsequence.md) - [EnumeratedSequence.Iterator](swift/enumeratedsequence/iterator.md) - [ExecuteDistributedTargetError](distributed/executedistributedtargeterror.md) - [ExecutorJob](swift/executorjob.md) - [FlattenSequence](swift/flattensequence.md) - [FlattenSequence.Index](swift/flattensequence/index.md) - [FlattenSequence.Iterator](swift/flattensequence/iterator.md) - [Float](swift/float.md) - [Float.SIMD16Storage](swift/float/simd16storage.md) - [Float.SIMD2Storage](swift/float/simd2storage.md) - [Float.SIMD32Storage](swift/float/simd32storage.md) - [Float.SIMD4Storage](swift/float/simd4storage.md) - [Float.SIMD64Storage](swift/float/simd64storage.md) - [Float.SIMD8Storage](swift/float/simd8storage.md) - [Float16](swift/float16.md) - [Float16.SIMD16Storage](swift/float16/simd16storage.md) - [Float16.SIMD2Storage](swift/float16/simd2storage.md) - [Float16.SIMD32Storage](swift/float16/simd32storage.md) - [Float16.SIMD4Storage](swift/float16/simd4storage.md) - [Float16.SIMD64Storage](swift/float16/simd64storage.md) - [Float16.SIMD8Storage](swift/float16/simd8storage.md) - [Float80](swift/float80.md) - [FloatingPointClassification](swift/floatingpointclassification.md) - [FloatingPointRoundingRule](swift/floatingpointroundingrule.md) - [FloatingPointSign](swift/floatingpointsign.md) - [Hasher](swift/hasher.md) - [IndexingIterator](swift/indexingiterator.md) - [InlineArray](swift/inlinearray.md) - [Int](swift/int.md) - [Int.SIMD16Storage](swift/int/simd16storage.md) - [Int.SIMD2Storage](swift/int/simd2storage.md) - [Int.SIMD32Storage](swift/int/simd32storage.md) - [Int.SIMD4Storage](swift/int/simd4storage.md) - [Int.SIMD64Storage](swift/int/simd64storage.md) - [Int.SIMD8Storage](swift/int/simd8storage.md) - [Int.Words](swift/int/words-swift.struct.md) - [Int128](swift/int128.md) - [Int16](swift/int16.md) - [Int16.SIMD16Storage](swift/int16/simd16storage.md) - [Int16.SIMD2Storage](swift/int16/simd2storage.md) - [Int16.SIMD32Storage](swift/int16/simd32storage.md) - [Int16.SIMD4Storage](swift/int16/simd4storage.md) - [Int16.SIMD64Storage](swift/int16/simd64storage.md) - [Int16.SIMD8Storage](swift/int16/simd8storage.md) - [Int16.Words](swift/int16/words-swift.struct.md) - [Int32](swift/int32.md) - [Int32.SIMD16Storage](swift/int32/simd16storage.md) - [Int32.SIMD2Storage](swift/int32/simd2storage.md) - [Int32.SIMD32Storage](swift/int32/simd32storage.md) - [Int32.SIMD4Storage](swift/int32/simd4storage.md) - [Int32.SIMD64Storage](swift/int32/simd64storage.md) - [Int32.SIMD8Storage](swift/int32/simd8storage.md) - [Int32.Words](swift/int32/words-swift.struct.md) - [Int64](swift/int64.md) - [Int64.SIMD16Storage](swift/int64/simd16storage.md) - [Int64.SIMD2Storage](swift/int64/simd2storage.md) - [Int64.SIMD32Storage](swift/int64/simd32storage.md) - [Int64.SIMD4Storage](swift/int64/simd4storage.md) - [Int64.SIMD64Storage](swift/int64/simd64storage.md) - [Int64.SIMD8Storage](swift/int64/simd8storage.md) - [Int64.Words](swift/int64/words-swift.struct.md) - [Int8](swift/int8.md) - [Int8.SIMD16Storage](swift/int8/simd16storage.md) - [Int8.SIMD2Storage](swift/int8/simd2storage.md) - [Int8.SIMD32Storage](swift/int8/simd32storage.md) - [Int8.SIMD4Storage](swift/int8/simd4storage.md) - [Int8.SIMD64Storage](swift/int8/simd64storage.md) - [Int8.SIMD8Storage](swift/int8/simd8storage.md) - [Int8.Words](swift/int8/words-swift.struct.md) - [IteratorSequence](swift/iteratorsequence.md) - [Job](swift/job.md) - [JobPriority](swift/jobpriority.md) - [JoinedSequence](swift/joinedsequence.md) - [JoinedSequence.Iterator](swift/joinedsequence/iterator.md) - [KeyValuePairs](swift/keyvaluepairs.md) - [LazyPrefixWhileSequence.Index](swift/lazyprefixwhilesequence/index.md) - [LazySequence](swift/lazysequence.md) - [LocalTestingActorID](distributed/localtestingactorid.md) - [LocalTestingDistributedActorSystem](distributed/localtestingdistributedactorsystem.md) - [LocalTestingDistributedActorSystemError](distributed/localtestingdistributedactorsystemerror.md) - [MainActor](swift/mainactor.md) - [MemoryLayout](swift/memorylayout.md) - [Mirror.DisplayStyle](swift/mirror/displaystyle-swift.enum.md) - [MutableRawSpan](swift/mutablerawspan.md) - [MutableSpan](swift/mutablespan.md) - [Mutex](synchronization/mutex.md) - [Never](swift/never.md) - [ObjectIdentifier](swift/objectidentifier.md) - [ObservationRegistrar](observation/observationregistrar.md) - [ObservationTracking](observation/observationtracking.md) - [ObservationTracking.Event.Kind](observation/observationtracking/event/kind-swift.struct.md) - [ObservationTracking.Options](observation/observationtracking/options.md) - [Observations](observation/observations.md) - [Observations.Iteration](observation/observations/iteration.md) - [Optional](swift/optional.md) - [OutputRawSpan](swift/outputrawspan.md) - [OutputSpan](swift/outputspan.md) - [PartialRangeFrom](swift/partialrangefrom.md) - [PartialRangeFrom.Iterator](swift/partialrangefrom/iterator.md) - [PartialRangeThrough](swift/partialrangethrough.md) - [PartialRangeUpTo](swift/partialrangeupto.md) - [PrefixSequence](swift/prefixsequence.md) - [PrefixSequence.Iterator](swift/prefixsequence/iterator.md) - [Range](swift/range.md) - [RangeSet](swift/rangeset.md) - [RangeSet.Ranges](swift/rangeset/ranges-swift.struct.md) - [RawSpan](swift/rawspan.md) - [Repeated](swift/repeated.md) - [Result](swift/result.md) - [ReversedCollection](swift/reversedcollection.md) - [ReversedCollection.Index](swift/reversedcollection/index.md) - [ReversedCollection.Iterator](swift/reversedcollection/iterator.md) - [SIMD16](swift/simd16.md) - [SIMD2](swift/simd2.md) - [SIMD3](swift/simd3.md) - [SIMD32](swift/simd32.md) - [SIMD4](swift/simd4.md) - [SIMD64](swift/simd64.md) - [SIMD8](swift/simd8.md) - [SIMDMask](swift/simdmask.md) - [Set](swift/set.md) - [Set.Index](swift/set/index.md) - [Set.Iterator](swift/set/iterator.md) - [Slice](swift/slice.md) - [Span](swift/span.md) - [StaticBigInt](swift/staticbigint.md) - [StaticString](swift/staticstring.md) - [StrideThrough](swift/stridethrough.md) - [StrideThroughIterator](swift/stridethroughiterator.md) - [StrideTo](swift/strideto.md) - [StrideToIterator](swift/stridetoiterator.md) - [String](swift/string.md) - [String.Comparator](swift/string/comparator.md) - [String.Encoding](swift/string/encoding.md) - [String.Index](swift/string/index.md) - [String.Iterator](swift/string/iterator.md) - [String.LocalizationValue](swift/string/localizationvalue.md) - [String.LocalizationValue.Placeholder](swift/string/localizationvalue/placeholder.md) - [String.StandardComparator](swift/string/standardcomparator.md) - [String.UTF16View](swift/string/utf16view.md) - [String.UTF16View.Iterator](swift/string/utf16view/iterator.md) - [String.UTF8View](swift/string/utf8view.md) - [String.UnicodeScalarView](swift/string/unicodescalarview.md) - [String.UnicodeScalarView.Iterator](swift/string/unicodescalarview/iterator.md) - [Substring](swift/substring.md) - [Substring.UTF16View](swift/substring/utf16view.md) - [Substring.UTF8View](swift/substring/utf8view.md) - [Substring.UnicodeScalarView](swift/substring/unicodescalarview.md) - [SuspendingClock](swift/suspendingclock.md) - [SuspendingClock.Instant](swift/suspendingclock/instant.md) - [SystemRandomNumberGenerator](swift/systemrandomnumbergenerator.md) - [Task](swift/task.md) - [TaskLocal](swift/tasklocal.md) - [TaskPriority](swift/taskpriority.md) - [UInt](swift/uint.md) - [UInt.SIMD16Storage](swift/uint/simd16storage.md) - [UInt.SIMD2Storage](swift/uint/simd2storage.md) - [UInt.SIMD32Storage](swift/uint/simd32storage.md) - [UInt.SIMD4Storage](swift/uint/simd4storage.md) - [UInt.SIMD64Storage](swift/uint/simd64storage.md) - [UInt.SIMD8Storage](swift/uint/simd8storage.md) - [UInt.Words](swift/uint/words-swift.struct.md) - [UInt128](swift/uint128.md) - [UInt128.Words](swift/uint128/words-swift.struct.md) - [UInt16](swift/uint16.md) - [UInt16.SIMD16Storage](swift/uint16/simd16storage.md) - [UInt16.SIMD2Storage](swift/uint16/simd2storage.md) - [UInt16.SIMD32Storage](swift/uint16/simd32storage.md) - [UInt16.SIMD4Storage](swift/uint16/simd4storage.md) - [UInt16.SIMD64Storage](swift/uint16/simd64storage.md) - [UInt16.SIMD8Storage](swift/uint16/simd8storage.md) - [UInt16.Words](swift/uint16/words-swift.struct.md) - [UInt32](swift/uint32.md) - [UInt32.SIMD16Storage](swift/uint32/simd16storage.md) - [UInt32.SIMD2Storage](swift/uint32/simd2storage.md) - [UInt32.SIMD32Storage](swift/uint32/simd32storage.md) - [UInt32.SIMD4Storage](swift/uint32/simd4storage.md) - [UInt32.SIMD64Storage](swift/uint32/simd64storage.md) - [UInt32.SIMD8Storage](swift/uint32/simd8storage.md) - [UInt32.Words](swift/uint32/words-swift.struct.md) - [UInt64](swift/uint64.md) - [UInt64.SIMD16Storage](swift/uint64/simd16storage.md) - [UInt64.SIMD2Storage](swift/uint64/simd2storage.md) - [UInt64.SIMD32Storage](swift/uint64/simd32storage.md) - [UInt64.SIMD4Storage](swift/uint64/simd4storage.md) - [UInt64.SIMD64Storage](swift/uint64/simd64storage.md) - [UInt64.SIMD8Storage](swift/uint64/simd8storage.md) - [UInt64.Words](swift/uint64/words-swift.struct.md) - [UInt8](swift/uint8.md) - [UInt8.SIMD16Storage](swift/uint8/simd16storage.md) - [UInt8.SIMD2Storage](swift/uint8/simd2storage.md) - [UInt8.SIMD32Storage](swift/uint8/simd32storage.md) - [UInt8.SIMD4Storage](swift/uint8/simd4storage.md) - [UInt8.SIMD64Storage](swift/uint8/simd64storage.md) - [UInt8.SIMD8Storage](swift/uint8/simd8storage.md) - [UInt8.Words](swift/uint8/words-swift.struct.md) - [UnboundedRange_](swift/unboundedrange_.md) - [UnfoldSequence](swift/unfoldsequence.md) - [Unicode](swift/unicode.md) - [Unicode.ASCII](swift/unicode/ascii.md) - [Unicode.ASCII.Parser](swift/unicode/ascii/parser.md) - [Unicode.CanonicalCombiningClass](swift/unicode/canonicalcombiningclass.md) - [Unicode.GeneralCategory](swift/unicode/generalcategory.md) - [Unicode.NumericType](swift/unicode/numerictype.md) - [Unicode.ParseResult](swift/unicode/parseresult.md) - [Unicode.Scalar](swift/unicode/scalar.md) - [Unicode.Scalar.Properties](swift/unicode/scalar/properties-swift.struct.md) - [Unicode.Scalar.UTF16View](swift/unicode/scalar/utf16view.md) - [Unicode.Scalar.UTF8View](swift/unicode/scalar/utf8view.md) - [Unicode.UTF16](swift/unicode/utf16.md) - [Unicode.UTF16.ForwardParser](swift/unicode/utf16/forwardparser.md) - [Unicode.UTF16.ReverseParser](swift/unicode/utf16/reverseparser.md) - [Unicode.UTF32](swift/unicode/utf32.md) - [Unicode.UTF32.Parser](swift/unicode/utf32/parser.md) - [Unicode.UTF8](swift/unicode/utf8.md) - [Unicode.UTF8.ForwardParser](swift/unicode/utf8/forwardparser.md) - [Unicode.UTF8.ReverseParser](swift/unicode/utf8/reverseparser.md) - [Unicode.UTF8.ValidationError](swift/unicode/utf8/validationerror.md) - [Unicode.UTF8.ValidationError.Kind](swift/unicode/utf8/validationerror/kind-swift.struct.md) - [UnicodeDecodingResult](swift/unicodedecodingresult.md) - [Unmanaged](swift/unmanaged.md) - [UnownedJob](swift/unownedjob.md) - [UnownedSerialExecutor](swift/unownedserialexecutor.md) - [UnownedTaskExecutor](swift/unownedtaskexecutor.md) - [UnsafeContinuation](swift/unsafecontinuation.md) - [WordPair](synchronization/wordpair.md) - [Zip2Sequence](swift/zip2sequence.md) - [Zip2Sequence.Iterator](swift/zip2sequence/iterator.md) ## See Also ### Actors - [Sendable](swift/sendable.md) - [Actor](swift/actor.md) - [AnyActor](swift/anyactor.md) - [MainActor](swift/mainactor.md) - [GlobalActor](swift/globalactor.md) - [ConcurrentValue](swift/concurrentvalue.md) - [UnsafeSendable](swift/unsafesendable.md) - [UnsafeConcurrentValue](swift/unsafeconcurrentvalue.md) - [isolation()](swift/isolation().md) - [extractIsolation(_:)](swift/extractisolation(_:).md)