Predicates
Dry-logic comes with a lot predicates to compose multiple rules:
require 'dry/logic'
require 'dry/logic/predicates'
include Dry::Logic
Now you can access all built-in predicates:
Predicates[:key?]
# => #<Method: Module(Dry::Logic::Predicates::Methods)#key?>
In the end predicates return true or false.
Predicates[:key?].(:name, {name: 'John'})
# => true
- Built-in:
type?none?key?attr?empty?filled?bool?date?date_time?time?number?int?float?decimal?str?hash?array?odd?even?lt?gt?lteq?gteq?size?min_size?max_size?bytesize?min_bytesize?max_bytesize?inclusion?exclusion?included_in?excluded_from?includes?excludes?eql?not_eql?is?case?true?false?format?respond_to?predicateuuid_v4?
With predicates you can build more composable and complex operations: For example, let's say we want to check that a given input is a hash and has a specify key.
require 'dry/logic'
require 'dry/logic/predicates'
include Dry::Logic
is_hash = Rule::Predicate.new(Predicates[:type?]).curry(Hash)
# => #<Dry::Logic::Rule::Predicate predicate=#<Method: Module(Dry::Logic::Predicates::Methods)#type?> options={:args=>[:hash]}>
name_key = Rule::Predicate.new(Predicates[:key?]).curry(:name)
# => #<Dry::Logic::Rule::Predicate predicate=#<Method: Module(Dry::Logic::Predicates::Methods)#key?> options={:args=>[:name]}>
hash_with_key = is_hash & name_key
# => #<Dry::Logic::Operations::And rules=[#<Dry::Logic::Rule::Predicate predicate=#<Method: Module(Dry::Logic::Predicates::Methods)#type?> options={:args=>[:hash]}>, #<Dry::Logic::Rule::Predicate predicate=#<Method: Module(Dry::Logic::Predicates::Methods)#key?> options={:args=>[:name]}>] options={}>
hash_with_key.(name: 'John').success?
# => true
hash_with_key.(not_valid: 'John').success?
# => false
hash_with_key.([1,2]).success?
# => false