Swift-Optional实质#

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public enum Optional<Wrapped> : _Reflectable, NilLiteralConvertible {
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    case None
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    case Some(Wrapped)
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    /// Construct a `nil` instance.
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    public init()
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    /// Construct a non-`nil` instance that stores `some`.
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    public init(_ some: Wrapped)
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    /// If `self == nil`, returns `nil`.  Otherwise, returns `f(self!)`.
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    @warn_unused_result
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    public func map<U>(@noescape f: (Wrapped) throws -> U) rethrows -> U?
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    /// Returns `nil` if `self` is `nil`, `f(self!)` otherwise.
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    @warn_unused_result
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    public func flatMap<U>(@noescape f: (Wrapped) throws -> U?) rethrows -> U?
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    /// Create an instance initialized with `nil`.
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    public init(nilLiteral: ())
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}