Symbolic constraints

Symbolic constraints make it possible to define the relations among components without referencing their attributes directly. The following symbolic constraints are available.

• Equality and inequality constraints. The equality constraint A==B says that A and B are the same and the inequality constraint A != B says that A and B are different. Here, A and B can be constants , attribute variables, or components, but the types of A and B must match each other. There two types of symbolic constants: String and Color. A constant string is any ASCII character sequence enclosed in "" and a constant color is one of the following:

         black, blue, cyan, darkGray, gray, green, lightGray, 
         magenta, orange, pink, red, white, yellow
  

     

• Position constraints. Constraints in this group relate the positions of two components. The following constraints belong to this group.

         inside(O1,O2) outside(O1,O2)
         left(O1,O2)   right(O1,O2)
         above(O1,O2)  below(O1,O2)
  

  The constraint R(O1,O2) can be read as " O1 is R O2." For instance, inside(O1,O2) says that the component O1 is inside the component O2.              

• sameXXX(O1,O2,...,On). This represents a group of constraints which enforce that the components O1, ..., On have the same value for the XXX attribute. We can replace sameXXX with one the following:

         sameX sameY sameCenterX sameCenterY sameLeftX sameRightX 
         sameSize sameWidth sameHeight 
         sameColor sameFont sameRow sameColumn
  

Symbolic constraints on arrays of components will be described in the Arrays section.