Can I have default initialize values without having to explicitly declare property name in child

Question

I am coming from the Java world but I tried to use a base class like this...

class Bicycle
  attr_reader :gears
  def initialize( gears: 1, 
    seats: 2, 
    wheels: 2 )
    @gears = gears
    @seats = seats
    @wheels = wheels
  end  
end  
class CrazyBicycle < Bicycle
  def initialize( seats: 2, 
    wheels: 2 )
    super(101, seats, wheels)
  end  
end  

b = CrazyBicycle.new(3, 4)
puts b.gears

This didn't work and throws Wrong number of arguments (given: 2, expected: 0). I can get it to work by being extremely explicit with param names. For example this does work...

class Bicycle
  attr_reader :gears
  def initialize( gears: 1, 
    seats: 2, 
    wheels: 2 )
    @gears = gears
    @seats = seats
    @wheels = wheels
  end  
end  
class CrazyBicycle < Bicycle
  def initialize( seats: 2, 
    wheels: 2 )
    super(gears: 101, seats: seats, wheels:wheels)
  end  
end  

b = CrazyBicycle.new(seats: 3,wheels: 4)
puts b.gears

But that seems like a lot of unnecessary variable names. Is there some sort of Ruby sugar I can use to prevent being that explicit?

Not directly related, but most Rubyists do not put method arguments on different lines. Yours is fine syntactically, but would be frowned upon by most Rubyists. — Kyle Heironimus, Dec 14 '17 at 18:23
or maybe https://stackoverflow.com/a/4557470/525478, which has defaults, but a similar concept... — Brad Werth, Dec 14 '17 at 18:29

Kyle Heironimus · Answer 1 · 2017-12-14T18:49:56.347

2

You are using keyword arguments, so must always pass the argument names when calling them. If you don't want to pass the argument name, remove the colon like so:

class Bicycle
  attr_reader :gears
  def initialize( gears = 1, 
    seats = 2, 
    wheels = 2 )
  ...
end

edited Dec 14 '17 at 18:49

answered Dec 14 '17 at 18:20

Kyle Heironimus

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score 0 · Answer 2 · answered Dec 14 '17 at 19:13

With keyword arguments you need to specify the argument name whenever that initialize method is called, even if that's indirectly via super:

class CrazyBicycle < Bicycle
  def initialize(seats: 2, wheels: 2)
    super(gears: 101, seats: seats, wheels: wheels)
  end  
end

Can I have default initialize values without having to explicitly declare property name in child

2 Answers2