Module: Karst::Value

Defined in:
lib/karst/value.rb

Overview

Small immutable value-object helper standing in for Ruby 3.2's Data.define, which Karst cannot rely on while supporting Ruby 2.7. Built on Struct(keyword_init: true), which already provides structural equality, keyword construction, and #members; the one thing Struct does not give for free is immutability, so .define freezes every instance its class produces. This matches Data's own contract exactly: the instance itself is frozen, but a member holding a mutable object (an Array, say) is not deep-frozen -- Data.define does not do that either, and Karst does not need it to.

Class Method Summary collapse

Class Method Details

.define(*members, &block) ⇒ Object

rubocop:disable Naming/BlockForwarding, Style/ArgumentsForwarding -- anonymous block forwarding (&) needs Ruby 3.1; this file runs on Ruby 2.7.



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# File 'lib/karst/value.rb', line 16

def self.define(*members, &block)
  klass = Struct.new(*members, keyword_init: true, &block)
  # rubocop:enable Naming/BlockForwarding, Style/ArgumentsForwarding

  # Struct.new itself is a heavily overloaded class method (it doubles as
  # the anonymous-subclass factory), so overriding it and calling super
  # would climb straight past Struct's own keyword-init handling into
  # that factory instead of a plain constructor. Overriding the ordinary
  # instance method #initialize has no such trap.
  klass.class_eval do
    def initialize(...)
      super
      freeze
    end
  end

  klass
end