定数フリーズまとめ

mutable_constant.rb

class MutableConstant
  SERVICE_TYPES1 = ["basic", "premium", "pro"]
  SERVICE_TYPES2 = ["basic", "premium", "pro"].freeze
  SERVICE_TYPES3 = ["basic", "premium", "pro"].map(&:freeze).freeze

  module Defaults
    SERVICE_TYPES1 = ["basic", "premium", "pro"]
    SERVICE_TYPES2 = ["basic", "premium", "pro"].freeze
    SERVICE_TYPES3 = ["basic", "premium", "pro"].map(&:freeze).freeze
  end

  Defaults.freeze

  def sample1(types)
    types.delete_if {|type| !type.nil? }
  end

  def sample2(types)
    types.map {|type| type << "_mode" }
  end
end

# 参照オブジェクトの書き換え
p MutableConstant.new.sample1(MutableConstant::SERVICE_TYPES1) #=> []
p MutableConstant.new.sample1(MutableConstant::SERVICE_TYPES2) #=> 12:in `delete_if': can't modify frozen Array (RuntimeError)

# 参照オブジェクトが保持するオブジェクトの書き換え
p MutableConstant.new.sample2(MutableConstant::SERVICE_TYPES2) #=> ["basic_mode", "premiam_mode", "pro_mode"]
p MutableConstant.new.sample2(MutableConstant::SERVICE_TYPES3) #=> 12:in `block in sample2': can't modify frozen String (RuntimeError)

# 定数の再定義
p MutableConstant::SERVICE_TYPES3 = 100 #=> 100 :22:in warning: already initialized constant MutableConstant::SERVICE_TYPES3
p MutableConstant::Defaults::SERVICE_TYPES3 = 100 #=> :31:in `<main>': can't modify frozen Module (RuntimeError)

👍

BTW, s/premiam/premium/g ?

typo is frozen so we can't fix them

Yes, I can.