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rubyinstance-variables

hash[key] is to hash.fetch(key) as @ivar is to what?

To expand on the title: How can I access an instance variable (@ivar) in a way that results in an exception if the instance variable hasn't been initialized?

Solution

  • There is no built in method that provides this functionality in respect to instance variables, however;

    Since Hash#[] is analogous to @ivar (or instance_variable_get(:@ivar)) in your example then Hash#fetch would be analogous to 

    def instance_variable_fetch(sym)
  raise(NameError, "instance variable not found: #{sym}") unless instance_variable_defined?(sym) 
  instance_variable_get(sym)
end

    Example: 

    @var = 42
instance_variable_fetch(:@var)
#=> 42
@ivar = nil
instance_variable_fetch(:@ivar)
#=> nil
instance_variable_fetch(:@other_var)
#=> NameError: instance variable not found: @other_var