Instance variable as parameter in initialize can be accessed without the @ prefix

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1

The output of the following code leaves me a little confused!

class Test
  def initialize(@value : String = "abcd")
	puts value ## without @ instance variable prefix char
  end
end
Test.new # => abcd

I guess it is Crystal’s syntactic sugar for initialization of instance variables that allows this, but nevertheless shouldn’t it raise an exception?

2

What would be the reason to prevent it? I’m pretty sure:

def initialize(@value : String = "abcd")
  puts value
end

gets re-written to

def initialize(value : String = "abcd")
  @value = value
  puts value
end

So it technically does exist.

3

Yes, that’s what I think too, but I find it a bit weird anyway.

4

Yes, ivar parameters are exposed as local variables.
One reason for this is that the parameter may have a type restriction that’s different from the ivar. For example when the ivar is nilable, but the parameter is not, the local variables has the same non-nil type.
Another use case is concurrency: When the method reads the ivar, it may have a different value than what was passed to the method call when it was assigned from a different fiber in the mean time.

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