Description

This library provides a way to ensure that certain objects always satisfy a specified set of constraints. An object that can be constrained must be a child of Constraint::Shell, which acts as a wrapper for the actual value. Constraints can added to subclasses and its instances (per-object constraints). It is possible to define methods that handle constraint violations and retrofit the object according to its definition.

The primary use of this library is to define "typed"/constrained arrays that may only contain certain elements that meet a set of requirements, e.g., non-nil, kind of some class, a certain attribute set …

With some help from the developer, this library can also be used (to some extent at least) to generate correct values and to find solutions fitting the set of constraints.

    class EvenInteger < Constraint::Shell
        and_constraint("Numeric") {|o, e| e.kind_of?(Integer)}
        and_constraint("Even") {|o, e| e.modulo(2) == 0}
    end

    enum = EvenInteger.new(2)
    enum.and_constraint("LT10") {|o, e| e < 10}

    p enum + 2
    => 4
    p enum + 1
    => Fixnum didn't meet constraint 'Even': 3 (ConstraintViolation)

or:

    class NumInRange < Constraint::Shell
        constraint_attr :min, 0
        constraint_attr :max, nil

        and_constraint('Numeric') {|o, e| e.kind_of?(Numeric)}
        and_constraint('InRange') {|o, e| o.min <= e && (!o.max || o.max >= e)}
        on_constraint_violation('InRange') {|o, e| (o.max && e > o.max) ? o.max : o.min}

        def generate_constrained_value(value)
            if value
                if !max or @max > value
                    value + 1
                else
                    raise Constraint::NoMoreValues
                end
            else
                @min
            end
        end
    end

    class Num1To10 < NumInRange
        @min = 1
        @max = 10
    end

    p Num1To10.new(5.2) + 2.2
    => 7.4
    p Num1To10.new(5.2) + 20.2
    => 10
    p Num1To10.new(5).collect_constrained_values
    => [5, 6, 7, 8, 9, 10]

Changes