constraint.rb

class ConstraintAttribute
  attr_reader :name
  attr_reader :multiplier
  attr_reader :constraint
  attr_reader :relation

  def initialize(constraint, name)
    @constraint, @name = constraint, name
    @constant, @multiplier = 0, 1
  end

  def ==(attribute)
    @constraint.create(attribute, :==)
  end

  def <=(attribute)
    @constraint.create(attribute, :<=)
  end

  def >=(attribute)
    @constraint.create(attribute, :>=)
  end

  def *(multiplier)
    @multiplier = multiplier
  end

  def +(constant)
    @constant = constant
  end

end

class Constraint
  attr_reader :view

  def initialize(view)
    @view = view
  end

  def create(related_attribute, relation)
    NSLayoutConstraint.constraintWithItem(
      @view,
      attribute:convert_attribute_name(@attribute_name),
      relatedBy:convert_relation(relation),
      toItem:related_attribute.constraint.view,
      attribute:convert_attribute_name(related_attribute.name),
      multiplier:related_attribute.multiplier,
      constant:related_attribute.constant
    )
  end

  def convert_relation(symbol)
    {
      :<= => NSLayoutRelationLessThanOrEqual,
      :== => NSLayoutRelationEqual,
      :>= => NSLayoutRelationGreaterThanOrEqual
    }[symbol]
  end

  AttributeNamesMap = {
      left:     NSLayoutAttributeLeft,
      right:    NSLayoutAttributeRight,
      top:      NSLayoutAttributeTop,
      bottom:   NSLayoutAttributeBottom,
      leading:  NSLayoutAttributeLeading,
      trailing: NSLayoutAttributeTrailing,
      width:    NSLayoutAttributeWidth,
      height:   NSLayoutAttributeHeight,
      center_x: NSLayoutAttributeCenterX,
      center_y: NSLayoutAttributeCenterY,
      baseline: NSLayoutAttributeBaseline,
      none:     NSLayoutAttributeNotAnAttribute
    }

  def convert_attribute_name(symbol)
    AttributeNamesMap[symbol]
  end

  AttributeNamesMap.keys.each do |key|
    define_method key, do
      @attribute = ConstraintAttribute.new(self, key)
    end
  end

end

def constraint(view)
  Constraint.new(view)
end

superview = UIView.new
view = UIView.new
view2 = UIView.new

c = constraint(view).width == constraint(view2).height * 1 + 10

superview.addSubview(view)
superview.addSubview(view2)
superview.addConstraint(c)