dry-rules-with-matcher.rb

require 'dry-validation'

ThreeDigits = /^\d{3}$/
FourDigits = /^\d{4}$/

schema = Dry::Validation.Schema do
  required(:field_1).filled(:str?)
  required(:field_2).filled(:str?)

  rule(field_2_depends_on_field_1: [:field_1, :field_2]) do |field_1, field_2|
    field_1.eql?('Foo').then(field_2.format?(ThreeDigits)) & field_1.eql?('Bar').then(field_2.format?(FourDigits))
  end
end

puts schema.call(field_1: 'Foo', field_2: '999').success?
puts schema.call(field_1: 'Bar', field_2: '999').success?
puts schema.call(field_1: 'Foo', field_2: '9999').success?
puts schema.call(field_1: 'Bar', field_2: '9999').success?