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rubyinstance-eval

Instance_eval does not work with do/end block, only with {}-blocks

If I have a class:

class KlassWithSecret
  def initialize
    @secret = 99
  end
end

and run:

puts KlassWithSecret.new.instance_eval { @secret }

it prints 99, but if I run:

puts KlassWithSecret.new.instance_eval do
  @secret
end

It returns an error: `instance_eval': wrong number of arguments (0 for 1..3) (ArgumentError)

Why can't I use do/end blocks with instance_eval?

P.S. I am using Ruby 2.1.0.

Solution

  • It's because when you pass block with curly braces, it is passed to instance_eval method. But if you pass it with do-end, it's passed to puts method, so instance_eval doesn't get block and raises an error.