Swift Guard Statement利用ケース ref: http://qiita.com/roothybrid7/items/beba0daf9bf7338f4874

[Class]CustomCollectionViewLayout.swift

class CustomCollectionViewLayout : UICollectionViewFlowLayout {
    var minimumLineSpacing: CGFloat = 0.0
    var minimumInteritemSpacing: CGFloat = 0.0
    var itemSize: CGSize = CGSizeMake(50, 50)
}

[Extension]CustomCollectionViewLayout.swift

extension CustomCollectionViewLayout {

    func minimumLineSpacingForSectionAtIndex(section: Int) -> CGFloat {
        guard let collectionView = self.collectionView, delegate = self.delegate else {
            return 0.0
        }
        guard let spacing = delegate.collectionView?(collectionView, layout: self, minimumLineSpacingForSectionAtIndex: section) else {
            return self.minimumLineSpacing
        }
        return spacing
    }

    func minimumInteritemSpacingForSectionAtIndex(section: Int) -> CGFloat {
        guard let collectionView = self.collectionView, delegate = self.delegate else {
            return 0.0
        }
        guard let spacing = delegate.collectionView?(collectionView, layout: self, minimumInteritemSpacingForSectionAtIndex: section) else {
            return self.minimumInteritemSpacing
        }
        return spacing
    }

    func insetForSectionAtIndex(section: Int) -> UIEdgeInsets {
        guard let collectionView = self.collectionView, delegate = self.delegate else {
            return UIEdgeInsetsZero
        }
        guard let inset = delegate.collectionView?(collectionView, layout: self, insetForSectionAtIndex: section) else {
            return self.sectionInset
        }
        return inset
    }

    func sizeForItemAtIndexPath(indexPath: NSIndexPath) -> CGSize {
        guard let collectionView = self.collectionView, delegate = self.delegate else {
            return CGSizeZero
        }
        guard let size = delegate.collectionView?(collectionView, layout: self, sizeForItemAtIndexPath: indexPath) else {
            return self.itemSize
        }
        return size
    }

}

CollectionViewController.swift

    // MARK: UICollectionViewDelegateFlowLayout

    func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAtIndex section: Int) -> UIEdgeInsets {
        return UIEdgeInsetsZero
    }

    func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAtIndex section: Int) -> CGFloat {
        return 2.0
    }

    func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumInteritemSpacingForSectionAtIndex section: Int) -> CGFloat {
        return 2.0
    }

errors.go

func (g *Gopher) WriteTo(w io.Writer) (size int64, err error) {
    err = binary.Write(w, binary.LittleEndian, int32(len(g.Name)))
    if err != nil {
        return
    }
    size += 4
    n, err := w.Write([]byte(g.Name))
    size += int64(n)
    if err != nil {
        return
    }
    err = binary.Write(w, binary.LittleEndian, int64(g.AgeYears))
    if err == nil {
        size += 4
    }
    return
}

guard.swift

func greet(person: [String: String]) {
    guard let name = person["name"] else {
        return
    }

    print("Hello \(name)!")

    guard let location = person["location"] else {
        print("I hope the weather is nice near you.")
        return
    }

    print("I hope the weather is nice in \(location).")
}

greet(["name": "John"])
// prints "Hello John!"
// prints "I hope the weather is nice near you."
greet(["name": "Jane", "location": "Cupertino"])
// prints "Hello Jane!"
// prints "I hope the weather is nice in Cupertino."