The Core iOS Developer’s Cookbook, Fifth Edition

Recipe: Comparing Constraints

All constraints use a fixed structure in the following form, along with an associated priority:

view1.attribute (relation) view2.attribute * multiplier + constant

Each element of this equation is exposed through a constraint’s object properties—namely priority, firstItem, firstAttribute, relation, secondItem, secondAttribute, multiplier, and constant. These properties make it easy to compare two constraints.

Views store and remove constraints as objects. If two constraints are stored in separate memory locations, they’re considered unequal, even if they describe the same conditions. To allow your code to add and remove constraints on-the-fly without storing those items locally, use comparisons.

Recipe 5-1 introduces ...