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Private setters in Ruby: What to do?

Normally, if you have a private method, you can’t call it with an explicit receiver, even if that receiver is self. So you can’t say

def foo
 self.bar  # explicit receiver
end

private
def bar
  123
end

Instead, foo needs to call simply bar, leaving the self implicit:

def foo
 bar  # implicit receiver
end

However, when you call setters, you always need an explicit receiver, or you’ll just assign a local variable:

def assign_things
  self.a = 123
  b = 456
end

def a=(v)
  puts "This one gets called."
end

def b=(v)
  raise "This one never does; the other method makes a local called `b` instead."
end

So, what do you do if you have a private setter? You call it with an explicit receiver:

def assign_things
  self.a = 123
end

private
def a=(v)
  puts "This is called successfully."
end

There’s a crazy special exception in Ruby that lets you use an explicit receiver of self with a setter just so that you can call private setters.

This strikes me as weird. Why can’t you call any private method explicitly on self? I thought it was just easier to implement Ruby if you couldn’t, but if they made it work for setters, I’m not sure what the big deal is.

Comments
  1. Eric Francis says:

    This is extremely useful. I could not figure out why my private setters were not working.

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