Sometimes I just want to get a given constraint

UIViewExtensions.swift

//
//  UIViewExtensions.swift
//
//  Created by Raúl Riera on 23/09/2015.
//  Copyright (c) 2015 Raul Riera. All rights reserved.
//

import UIKit

extension UIView {
    /**
    Returns the matching attribute constraint held by the view.
    
    - parameter attribute: attribute of the constraint
    - returns: the matching constraint
    */
    public func layoutConstraint(attribute attribute: NSLayoutAttribute) -> NSLayoutConstraint? {
        return layoutConstraints(attributes: [attribute]).first
    }
    
    /**
    Returns the matching attribute constraints held by the view.
    
    - parameter attribute: of the constraints
    - returns: the matching constraints
    */
    public func layoutConstraints(attribute attribute: NSLayoutAttribute) -> [NSLayoutConstraint] {
        return layoutConstraints(attributes: [attribute])
    }
    
    /**
    Returns the matching attributes constraints held by the view.
    
    - parameter attributes: array of attributes of the constraints
    - returns: the matching constraints
    */
    public func layoutConstraints(attributes attributes: [NSLayoutAttribute]) -> [NSLayoutConstraint] {
        var layoutConstraints = [NSLayoutConstraint]()
        
        if let superviewConstrains = superview?.constraints {
            layoutConstraints += superviewConstrains
        }
        
        layoutConstraints += constraints
        
        let filteredConstraints = layoutConstraints.filter { (layoutConstraint) in
            return attributes.contains(layoutConstraint.firstAttribute)
        }.filter { (layoutConstraint) in
            if let secondItem: AnyObject = layoutConstraint.secondItem {
                return layoutConstraint.firstItem.isEqual(self) || secondItem.isEqual(self)
            } else {
                return layoutConstraint.firstItem.isEqual(self)
            }
        }
        
        return filteredConstraints
    }

}