Binary operators, coerce, and non numeric types

ruby-talk
1

okay, i understand how to define a coerce method, but i don't think it
can do what i want, in fact i think the only way to do what i want is
rather ugly unless i drill down and actually patch the interpreter.

class X
  def + other
    BinOp.new(self,other,:+)
  end
end

class BinOp
  def initialize x,y,op
    @x,@y,@op=x,y,op
  end
end

x = X.new

x + x # -> BinOp, the behaviour i want
x + 3 # -> BinOp, the behaviour i want
3 + 3 # -> 6, the behaviour i want
3 + x # is of courses an error, but i want it to return a BinOp

the only way i can find that ruby will support this, is by writing

class Fixnum
  alias old_add +
  def + other
    if other.kind_of? X
      BinOp.new self, other, :+
    else
      self.old_add other
    end
  end
end

which is pretty ugly considering i have many operators to support, as
well as several numeric types. of course i could automate it with some
metaprogramming, but i'd like to know if anyone has any better ideas?

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2

ok i hadn't fully grokked coerce, and have found a solution. just incase
anybody is interested:

class X

  def + other
    bin_op other, :+
  end
  def ** other
    bin_op other, :**
  end
  def - other
    bin_op other, :-
  end
  def / other
    bin_op other, :confused:
  end

  def bin_op other, op
    if @coerced
      @coerced = false
      BinOp.new other, self, op
    else
      BinOp.new self, other, op
    end
  end

  def coerce other
    @coerced = true
    [self,other]
  end

end

class BinOp
  def initialize x,y,op
    @x, @y, @op = x, y, op
  end
  def to_s
    "BinOp #@x #@op #@y"
  end
end

x = X.new

puts x + 3
puts 3.0 + x
puts 2 - x
puts x - 10
puts 23 ** x
puts 2.99 / x
puts x / -1

cheers,
_c

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