Class: Value

Inherits:
Object
  • Object
show all
Defined in:
lib/values.rb

Overview

Simple immutable value objects for ruby.

Examples:

Make a new value class:

Point = Value.new(:x, :y)

And use it:

p = Point.new(1, 0)
p.x
#=> 1
p.y
#=> 0

Class Method Summary collapse

Class Method Details

.new(*fields, &block) ⇒ Class

Create a new value class.

Parameters:

  • fields (Array<Symbol>) —

    Names of fields to create in the new value class

  • block (Proc) —

    Optionally, a block to further define the new value class

Returns:

  • (Class) —

    A new value class with the provided fields

Raises:

  • (ArgumentError) —

    If no field names are provided



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# File 'lib/values.rb', line 20

def self.new(*fields, &block)
  raise ArgumentError.new('wrong number of arguments (0 for 1+)') if fields.empty?

  Class.new do
    attr_reader(:hash, *fields)

    define_method(:initialize) do |*values|
      raise ArgumentError.new("wrong number of arguments, #{values.size} for #{fields.size}") if fields.size != values.size

      fields.zip(values) do |field, value|
        instance_variable_set(:"@#{field}", value)
      end

      @hash = self.class.hash ^ values.hash

      freeze
    end

    const_set :VALUE_ATTRS, fields

    def self.with(hash)
      unexpected_keys = hash.keys - self::VALUE_ATTRS
      if unexpected_keys.any?
        raise ArgumentError.new("Unexpected hash keys: #{unexpected_keys}")
      end

      missing_keys = self::VALUE_ATTRS - hash.keys
      if missing_keys.any?
        raise ArgumentError.new("Missing hash keys: #{missing_keys} (got keys #{hash.keys})")
      end

      new(*hash.values_at(*self::VALUE_ATTRS))
    end

    def ==(other)
      eql?(other)
    end

    def eql?(other)
      self.class == other.class && values == other.values
    end

    def values
      self.class::VALUE_ATTRS.map { |field| send(field) }
    end

    def inspect
      attributes = to_a.map { |field, value| "#{field}=#{value.inspect}" }.join(", ")
      "#<#{self.class.name} #{attributes}>"
    end

    def with(hash = {})
      return self if hash.empty?
      self.class.with(to_h.merge(hash))
    end

    def to_h
      Hash[to_a]
    end

    def to_a
      self.class::VALUE_ATTRS.map { |field| [field, send(field)] }
    end

    class_eval &block if block
  end
end