Adding a key only to a hash based on an if statement

Question

Typically, we define a hash as

h={:a=>val1, :b=>val2}

However, i want to add a condition to only add in the key :b if val2 is not a nil value. Something like

h={:a=>val1}
h[:b]=val2 if val2

But can it be encapsulated in a single line?

Answer 1

h[:b] = val unless val.nil?

Answer 2

You could override the []= operator for just that one hash, or make a subclass of Hash and override it there.

hash = {}

class << hash
  def []=(key, value)
    case key
    when :b
      raise StandardError("Invalid :b value") if value.nil?
    end

    super(key,value)
  end
end

hash[:a] = 10
hash[:b] = nil  # Will raise exception

Answer 3

h = { :a => val1 }.merge(val2 ? { :b => val2 } : {})

But don't do this. Just keep it simple.

Answer 4

You don't have to worry about nil elements in hash, because you can simply clean up hash from them:

{:a => 1, :b => nil}.reject { |k, v| v.nil? } # {:a => 1}