Ivars

@dynamicMemberLookup
public struct Ivars<IvarType>

A wrapper around an object for accessing Objective-C instance variables of type IvarType on it.

This type supports dynamic member lookup, which means that ivars can be accessed as if they were members of the type. Note that if an ivar with the given name does not exist, the dynamic member access will result in a crash.

  • To access a pointer to the ivar instead, use Ivars.withIvar(_:_:).

  • To fail gracefully if the ivar does not exist, use Ivars.subscript(safelyAccessing:).

  • To access an ivar with a name that clashes with an actual member on this type, it is possible to use Ivars.subscript(dynamicMember:) directly.

  • To access a weak ivar, pass .weak as the second argument to the Ivars initializer. The IvarType must correspond to an optional of a class (e.g. Ivars<NSString?>).

Example

let object = MyObject(foo: 5)
Ivars<Int>(object)._foo // 5
Ivars(object)._foo = 7
print(object.foo) // 7
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  • Construct a new instance of Ivars for accessing Objective-C instance variables on object.

    Declaration

    Swift

    public init(_ object: AnyObject)

    Parameters

    object

    The object on which ivars are to be accessed.
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  • Access an Objective-C instance variable on the object.

    It is safe to assume that body will be called on all execution paths.

    Warning

    The pointer argument should not be stored and used outside of the lifetime of the call to the closure.

    Declaration

    Swift

    public func withIvar<Result>(
    _ name: String,
    _ body: (_ pointer: UnsafeMutablePointer<IvarType>?) throws -> Result
) rethrows -> Result

    Parameters

    name

    The name of the instance variable to access.
    body

    A block which receives a pointer to the ivar, within which it may be read or written to.
    pointer

    The pointer to the ivar, or nil if object does not have an ivar with the provided name.

    Return Value

    The value returned from body.

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  • Access an Objective-C instance variable on the object, failing gracefully if the instance variable does not exist.

    Note

    If the setter is passed a value of nil, it will do nothing.

    Declaration

    Swift

    public subscript(safelyAccessing ivarName: String) -> IvarType? { get nonmutating set }

    Parameters

    ivarName

    The name of the instance variable to access.

    Return Value

    The value of the instance variable, or nil if there is no ivar with the given name.

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  • Access an Objective-C instance variable on the object.

    Precondition

    The ivar ivarName must be present on the object. If an ivar with the given name is not present, using this subscript will result in a crash.

    To fail gracefully, use Ivars.subscript(safelyAccessing:) or Ivars.withIvar(_:_:).

    Declaration

    Swift

    public subscript(dynamicMember ivarName: String) -> IvarType { get nonmutating set }

    Parameters

    ivarName

    The name of the instance variable to access.
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Available where IvarType: OptionalProtocol, IvarType.Wrapped: AnyObject

  • Construct a new instance of Ivars for accessing weak Objective-C instance variables on object.

    This initializer requires that IvarType be an optional object type.

    For example, to access a weak string ivar _foo on obj, you could use Ivars<NSString?>(obj, .weak)._foo.

    Declaration

    Swift

    public init(_ object: AnyObject, _ storage: WeakStorage)

    Parameters

    object

    The object on which ivars are to be accessed.
    storage

    Set this to WeakStorage.weak. Indicates that the instance variable is weak.
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