[swift-dev] [RFC] UnsafeBytePointer API for In-Memory Layout

[Joe Groff]

> On May 12, 2016, at 9:27 AM, Jordan Rose via swift-dev <swift-dev at swift.org> wrote:
> 
> 
> - I’m uncomfortable with using the term “undefined behavior” as if it’s universally understood. Up until now we haven't formally had that notion in Swift, just “type safety” and “memory safety” and “invariant-preserving” and the like. Maybe we need it now, but I think it needs to be explicitly defined. (I’d actually talk to Dave about exactly what terms make the most sense for users.)

We do have undefined behavior, and use that term in the standard library docs where appropriate:

stdlib/public/core/Optional.swift-  /// `!` (forced unwrap) operator. However, in optimized builds (`-O`), no
stdlib/public/core/Optional.swift-  /// check is performed to ensure that the current instance actually has a
stdlib/public/core/Optional.swift-  /// value. Accessing this property in the case of a `nil` value is a serious
stdlib/public/core/Optional.swift:  /// programming error and could lead to undefined behavior or a runtime
stdlib/public/core/Optional.swift-  /// error.
stdlib/public/core/Optional.swift-  ///
stdlib/public/core/Optional.swift-  /// In debug builds (`-Onone`), the `unsafelyUnwrapped` property has the same
--
stdlib/public/core/StringBridge.swift-  /// The caller of this function guarantees that the closure 'body' does not
stdlib/public/core/StringBridge.swift-  /// escape the object referenced by the opaque pointer passed to it or
stdlib/public/core/StringBridge.swift-  /// anything transitively reachable form this object. Doing so
stdlib/public/core/StringBridge.swift:  /// will result in undefined behavior.
stdlib/public/core/StringBridge.swift-  @_semantics("self_no_escaping_closure")
stdlib/public/core/StringBridge.swift-  func _unsafeWithNotEscapedSelfPointer<Result>(
stdlib/public/core/StringBridge.swift-    _ body: @noescape (OpaquePointer) throws -> Result
--
stdlib/public/core/Unmanaged.swift-  /// reference's lifetime fixed for the duration of the
stdlib/public/core/Unmanaged.swift-  /// '_withUnsafeGuaranteedRef' call.
stdlib/public/core/Unmanaged.swift-  ///
stdlib/public/core/Unmanaged.swift:  /// Violation of this will incur undefined behavior.
stdlib/public/core/Unmanaged.swift-  ///
stdlib/public/core/Unmanaged.swift-  /// A lifetime of a reference 'the instance' is fixed over a point in the
stdlib/public/core/Unmanaged.swift-  /// programm if:

-Joe
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