Yield with self does not work when calling operator methods

Help & Support
1

I am trying to create a DSL with operator methods. However, in a “with self yield” block, the operators don’t work.

Given following code:

class Adder
  getter ns : Array(Int32) = [] of Int32

  def add=(n : Int32)
    ns.push n
  end

  def min(n : Int32)
    ns.push (-1 * n)
  end

  def calc(&)
    with self yield
  end
end

adder = Adder.new
puts adder.ns
adder.add = 1
puts adder.ns
adder.calc do
  add = 2
end
puts adder.ns
adder.min(3)
puts adder.ns
adder.calc do
  min(4)
end
puts adder.ns

I get output


[1]
[1]
[1, -3]
[1, -3, -4]

But I expected


[1]
[1, 2]
[1, 2, -3]
[1, 2, -3, -4]

Is it possible to use operator methods in a “with self yield” block?

2

Think the problem here is add = 2 is ambiguous, so the compiler is assuming it’s a local variable assignment. If you want it to call the setter, you can do itself.add = 2. Tho really a more practical solution would be to use a more idiomatic method name, like def <<(n : Int32) and/or push to make it more clear and not involve assignment so compiler will know what to do.

3

Thanks for your quick answer!

The “add” and “minus” was just an example. In my DSL, I’ve got a lot of configuration options that can be set by assignment operator. The idea is to set options that can occur only once by assignment (=), and options that can occur multiple times by <<.

I’ll see if there’s another operator I can use instead of = for options I can set once.