Convert hash params into instance variables on Ruby initializer

Question

I have this class:

class PriceChange
  attr_accessor :distributor_id, :product_id, :value, :price_changed_at, :realm

  def initialize(data = {})
    @distributor_id   = data[:distributor_id]
    @product_id       = data[:product_id]
    @value            = data[:value]
    @price_changed_at = data[:price_changed_at]
    @realm            = data[:realm]
  end
end

And I want to avoid the mapping inside the method body. I want a transparent and elegant way to set the instance attributes values. I know I can iterate through the data keys and use something like define_method. I don't want this. I want to do this in a clean way.

Andrey Deineko · Accepted Answer · 2017-04-04 15:52:38Z

5

I want to do this in a clean way.

You won't get attr_accessors and instance variables without defining them. The below is using some simple metaprogramming (does it qualify for "clean"?)

class PriceChange
  def initialize(data = {})
    data.each_pair do |key, value|
      instance_variable_set("@#{key}", value)
      self.class.instance_eval { attr_accessor key.to_sym }
    end
  end
end

Usage:

price_change = PriceChange.new(foo: :foo, bar: :bar)
#=> #<PriceChange:0x007fb3a1755178 @bar=:bar, @foo=:foo>
price_change.foo
#=> :foo
price_change.foo = :baz
#=> :baz
price_change.foo
#=> :baz

edited Apr 4, 2017 at 15:52

answered Apr 4, 2017 at 15:39

Andrey Deineko

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2 Comments

Leantraxxx Over a year ago

Your code is undoubtedly very clean but, as I said: "I know I can iterate through the data keys and use something like define_method". I'm looking for a "transparent" way. Maybe does not exist.

Andrey Deineko Over a year ago

@Leantraxxx it does not exist, AFAICT

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