Simple deep-dive hash access when it's likely a key may be missing.

output.txt

"Foo Bar!"
nil
nil
nil
"One"
"****************************************"
"Foo Bar!"
"boom"
"boom"
"boom"
"One"

safe_hash_values.rb

foo = {
  fe: "One",
  fo:  "Foe",
  bar: {
    baz: {
      foobar: "Foo Bar!"
    }
  }
}

module SafeHashValues
  def value_at *keys

    keys.reduce(self) do |m, k| 
      if m.respond_to?(:fetch) 
        m.fetch(k) { yield if block_given? } 
      else 
        yield if block_given?
      end
    end
  end
end

def log value
  puts value.inspect
end

foo.extend(SafeHashValues)
log foo.value_at(:bar, :baz, :foobar)
log foo.value_at(:bar, :baz, :foobar, :bang)
log foo.value_at(:bar, :baz, :foobar, :bang)
log foo.value_at :bar, :bat, :foobar
log foo.value_at :fe
log '*' * 40
log foo.value_at(:bar, :baz, :foobar) { "boom" }
log foo.value_at(:bar, :baz, :foobar, :bang) { "boom" }
log foo.value_at(:bar, :baz, :foobar, :bang) { "boom" }
log foo.value_at(:bar, :bat, :foobar) { "boom" }
log foo.value_at(:fe) { "boom" }