MyHash_one_liner.rb

require "rspec/autorun"

class MyHash < Hash
  undef_method :fetch

  # Implement the method fetch without using `super`
  # HINT: replace star with the argument(s) you want
  def fetch(key, value=NameError, &block)
    (has_key?(key))? self[key] : return_value_or_raise_exception(value, &block)
  end

  private 

  def return_value_or_raise_exception(value, &block)
    raise KeyError, 'key not in the array' if arguments_missing?(value, &block)
    (block_given?)? yield : value
  end

  def arguments_missing?(value, &block)
    value == NameError && !block_given?
  end
end

RSpec.describe MyHash do
  subject{ MyHash[:foo, "foo", :bar, "bar"] }

  it "gets the value by key" do
    expect(subject.fetch(:foo)).to eq("foo")
  end

  it "raises KeyError when trying to access non-existing key" do
    expect{ subject.fetch(:baz) }.to raise_error(KeyError)
  end

  it "returns the second argument when trying to access non-existing key" do
    expect(subject.fetch(:baz, "set value")).to eq("set value")
    expect(subject.fetch(:baz, nil)).to be_nil
    expect(subject.fetch(:baz, false)).to eq false
  end

  it "executes block if given when trying to access non-existent key" do
    expect(subject.fetch(:baz){ "set value" }).to eq("set value")
    expect(subject.fetch(:baz, "no good"){ "set value" }).to eq("set value")
  end
end