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This attribute can be attached to a noncopyable struct to specify that its storage is raw, meaning the type definition is (with some limitations) able to do as it pleases with the storage. This provides a basis for implementing types for things like atomics, locks, and data structures that use inline storage to store conditionally-initialized values. The example in `test/Prototypes/UnfairLock.swift` demonstrates the use of a raw layout type to wrap Darwin's `os_unfair_lock` APIs, allowing a lock value to be stored inside of classes or other types without needing a separate allocation, and using the borrow model to enforce safe access to lock-guarded storage.
30 lines
970 B
Swift
30 lines
970 B
Swift
// RUN: %target-swift-frontend -enable-experimental-feature RawLayout -parse -verify %s
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@_rawLayout(size: 4, alignment: 4)
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struct Lock: ~Copyable {}
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@_rawLayout(like: Int)
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struct Lock2: ~Copyable {}
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@_rawLayout(like: Optional<Int>)
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struct Lock3: ~Copyable {}
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@_rawLayout(like: T)
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struct MyUnmanaged<T>: ~Copyable {}
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@_rawLayout(likeArrayOf: T, count: 8)
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struct SmallVectorBuf<T>: ~Copyable {}
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@_rawLayout // expected-error{{expected '('}}
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struct NoLayoutSpecified: ~Copyable {}
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@_rawLayout() // expected-error{{expected 'size', 'like', or 'likeArrayOf' argument to @_rawLayout attribute}}
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struct NoParamsSpecified: ~Copyable {}
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@_rawLayout(size: 4) // expected-error{{expected alignment argument after size argument in @_rawLayout attribute}}
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struct SizeWithoutAlignment: ~Copyable {}
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@_rawLayout(likeArrayOf: Optional<Int>) // expected-error{{expected count argument after likeArrayOf argument in @_rawLayout attribute}}
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struct ArrayWithoutSize: ~Copyable {}
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