Discussion on: Simple memorization

[jakebman]

(Disclaimer - I've never written Ruby, but I'm assuming || is logical or - a || b is a if a is true, otherwise b)

I believe that ||= might not work very well if you try to memoize false.

The point of memoization is that once a value is set, you don't change it:

it 'smilers never "CRY"' do
  expect(smile.smile).to be_nil
  expect(smile.ensmile).to eq 'SMILE'
  expect(smile.ensmile(cry: true)).to eq 'SMILE'
  expect(smile.smile).to eq 'SMILE'
end

it 'criers never "SMILE"' do
  expect(smile.smile).to be_nil
  expect(smile.ensmile(cry: true)).to eq 'CRY'
  expect(smile.ensmile).to eq 'CRY'
  expect(smile.smile).to eq 'CRY'
end

Consider a boolean property instead:

class Smile
  attr_accessor :smiling

  def ensmile(cry: false)
    @smiling ||= begin
      !cry
    end
  end
end

And test that criers never smile:

it 'criers never "SMILE"' do
  expect(smile.smiling).to be_nil
  expect(smile.ensmile(cry: true)).to eq false
  expect(smile.ensmile).to eq false # Failure here
  expect(smile.smiling).to eq false # And here, for the same reason
end