Setter method (assignment) with multiple arguments

Question

I have a custom class and want to be able to override the assignment operator. Here is an example:

class MyArray < Array
  attr_accessor :direction
  def initialize
    @direction = :forward
  end
end
class History
  def initialize
    @strategy = MyArray.new
  end
  def strategy=(strategy, direction = :forward)
    @strategy << strategy
    @strategy.direction = direction
  end
end

This currently doesn't work as intended. upon using

h = History.new
h.strategy = :mystrategy, :backward

[:mystrategy, :backward] gets assigned to the strategy variable and the direction variable remains :forward.
The important part is that I want to be able to assign a standard value to the direction parameter.

Any clues to make this work are highly appreciated.

Answer 1

Due to the syntax sugar of methods whose names end in=, the only way that you can actually pass multiple parameters to the method is to bypass the syntax sugar and use send…

h.send(:strategy=, :mystrategy, :backward )

…in which case you might as well just use a normal method with better names:

h.set_strategy :mystrategy, :backward

However, you could rewrite your method to automatically un-array the values if you knew that an array is never legal for the parameter:

def strategy=( value )
  if value.is_a?( Array )
    @strategy << value.first
    @strategy.direction = value.last
  else
    @strategy = value
  end
end

This seems like a gross hack to me, however. I would use a non-assigment method name with multiple arguments if you need them.

---

An alternative suggestion: if the only directions are :forward and :backward what about:

def forward_strategy=( name )
  @strategy << name
  @strategy.direction = :forward
end

def reverse_strategy=( name )
  @strategy << name
  @strategy.direction = :backward
end

Answer 2

The problem is

def strategy=(strategy, direction = :forward)
  @strategy = strategy
  @strategy.direction = direction
end

When you set

h.strategy = :mystrategy, :backward

you are actually overriding the original @strategy instance. After that call, @strategy is an instance of Symbol, not MyArray.

What do you want to do? Replace the object or update it?