Any way to make instance variables private

Help & Support
1

I wanted to know if there is a way we can make instance variables inaccessible outside of the class. For example, the following snippet (which works and prints 30):

class Point
  @x : Int32
  @y : Int32
  
  def initialize(@x, @y)
  end
end
  
point = Point.new(10, 20)
  
puts point.@x + point.@y

What if I wanted @x and @y not be accessible from outside the class if I do not define any getter or property. I think I read in a discussion that instance variables are private by default, is that only in case of writes?

Thanks in advance. I just started learning Crystal two days ago so if I have missed the obvious then apologies in advance too.

2

There is no way to do that. Instance variables are actually public, but you should write code as if they were private. So here you should use two getters.

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3

Put differently, accessing instance variables directly is a smell and should be avoided 99.9% of the time.

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4

Even if we remove the syntax to access an instance variable from outside of a class, anyone can reopen your class and add getters for them. In Ruby this is almost the same, you have a method called instamcr_variable_get.

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5

Thank you very much everyone, I titally agree and just wanted to verify. This code smell has a pretty strong scent since a .@ will give it away upon visual inspection. The 0.01% of the time I can see myself using it is when I’m debugging and even that would be temporary.

It’s awesome to have replies so fast. Y’all are awesome :)

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6

tbh I didn’t even know this was legal syntax

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7

I didn’t even knew that writing foo.@bar was possible :astonished:

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8

I think we should probably document it as a current behavior that you shouldn’t rely on, even if it’s a breaking change.

Ideally, I’d like that syntax to only be able to access instance variables of the same scope.

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