Ruby Data Class: Immutability Workarounds/

#ruby #immutability #valueobjects #datastructures

This is part 3 in this series on Ruby's Data Class. Part 1 covered Syntax and part 2 compared Data with Struct.

Immutability Workarounds, Sort of

We can work (arguably) against the intent of Data in some ways.

For example, when an attribute is set to a Hash, we can update values in the hash.

ColorCounts = Data.define(:color_tally)
# => Colorcounts

screen_colors = ColorCounts.new({red: 0, blue: 0, green: 0})
# => #<data ColorCounts color_tally={:red=>0, :blue=>0, :green=>0}>

# Update a value in `color_tally`
screen_colors.color_tally[:red] += 5
# => 5

# Note that the value for  `:red` has been updated
screen_colors.color_tally
# => {:red=>5, :blue=>0, :green=>0}

We can also workaround to update a (non-frozen) string.

Example:

Person = Data.define(:name)
# => Person

me = Person.new(name: +'Popko')
# => #<data Person name="Popko">

me.name.prepend 'Kelly '
# => 'Kelly Popko'

me.name
# => 'Kelly Popko'

So we are not completely without the ability to modify or create certain workarounds.

However, when we need more flexibility or mutability, for example, we would want to choose class or something else more suited to what we need instead of trying to work around it with Data.