How to return all properties of a class/struct in a string delimited list?

1

Example code:

class Portal
  property zone_to = 0
  property x = 0f32
  property y = 0f32
  property owner_id = 0

  def initialize(@x, @y, @owner_id, @zone_to)
  end

  def prop_string()
    "#{zone_to},#{x},#{y},#{owner_id}"
  end
end

p = Portal.new(1f32,1f32,1,1)

pp p.prop_string

However, is it possible to do this dynamically so we don’t have to hard-code the variable in prop_string each time we add a new property to the class?

edit: Hmm… something something macros :stuck_out_tongue:

2

DAMN! I think I got it!

class Portal
  property zone_to = 0
  property x = 0f32
  property y = 0f32
  property owner_id = 0

  def initialize(@x, @y, @owner_id, @zone_to)
  end
  
  def prop_string()
    array_string = Array(String).new
    {% for v in @type.instance_vars %}
      array_string << {{v}}.to_s
     {% end %}
    array_string.join(",")
  end
end

p = Portal.new(1f32,1f32,1,1)

pp p.prop_string

All by myself :slight_smile: Any thoughts / improvements?

edit: Damn, macros are aweeesomeee!

1 Like
3

Could simplify it to {{@type.instance_vars.map(&.id)}}.join(','). This way the only thing that is happening at runtime is the join.

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4

Oh neato! Yeah that’s way nicer and easier to read lol, ty

5

You can even avoid the runtime join by doing it in the macro. {{@type.instance_vars.map(&.id).join(‘,’)}} will perform the join at compile time and you don’t even have to pay the runtime cost of allocating the string.

6

That wouldn’t work. That would result in the string being the names of each property joined together, like "zone_to,x,y,owner_id". It has to happen at runtime as it needs to join the runtime values of each ivar.

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7

Ah, sorry. I thought the names are what we were talking about. :joy:

8

You could even use a tuple, to avoid allocating an array!

{% begin %}
  { {{@type.instance_vars.map(&.id).splat}} }.join(',')
{% end %}
3 Likes
9

Yeah, I probably should have wrote property values :laughing:

More explicit hahaha

1 Like