Class: Mementus::Model::Value

Inherits:
Object
  • Object
show all
Defined in:
lib/mementus/model/value.rb

Overview

Value object with comparison by value equality.

This is a wrapper class, used as a factory for generating instances of Ruby structs that wraps the Struct constructor with method advice to handle validation (and eventually type coercion if needed).

Class Method Summary collapse

Class Method Details

.define(*slots, **fields, &block) ⇒ Object 



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# File 'lib/mementus/model/value.rb', line 13

def self.define(*slots, **fields, &block)
  # Cannot define a Value without specifying slots or fields
  if slots.empty? && fields.empty?
    raise ArgumentError.new("missing attribute definition")
  end

  # Build and validate an attribute specification matching the stdlib
  # constructor convention
  slots_spec, fields_spec = if fields.any?
    raise ArgumentError.new("cannot use slots when field map is supplied") if slots.any?
    [fields.keys, fields]
  else
    [slots, Hash[slots.map { |s| [s, Type::Any]}]]
  end

  validator = Validator.new(fields_spec)

  # Define a new struct with the given specification of attributes
  struct = Struct.new(*slots_spec, keyword_init: true, &block)

  # Method advice wrapping the stdlib constructor
  struct.define_method :initialize do |*args, **kwargs|

    # Handles the original stdlib API of slot-based args if you really
    # must do things this way. The keyword args API is the preferred
    # approach.
    attr_values = if args.any?
      raise ArgumentError.new("cannot mix slots and kwargs") if kwargs.any?
      Hash[slots.zip(args)]
    else
      kwargs
    end

    # Check that the provided values match the defined attributes and types
    validator.check(attr_values)

    # TODO: type coercion or mapping decision goes here

    super(**attr_values)

    # Freeze the instance before returning to caller
    # TODO: if immutability becomes optional this needs to be wrapped
    freeze
  end

  struct
end

.new(*slots, **fields, &block) ⇒ Object 



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# File 'lib/mementus/model/value.rb', line 9

def self.new(*slots, **fields, &block)
  define(*slots, **fields, &block)
end