Today, I Learned...

city = "Philadelphia"
city.frozen? # => false
city << ", PA"
city # => "Philadelphia, PA"

# frozen_string_literal: true

city = "Philadelphia"
city.frozen? # => true
city << ", PA" # RuntimeError: can't modify frozen String

a = 1.23
b = nil

a.round # => 1
b.round # NoMethodError: undefined method `round' for nil:NilClass

a&.round # => 1
b&.round # => nil

nil&.none&.of&.these&.methods&.exist # => nil

data = {
  users: [
    {
      name: "Justin",
      cats: [
        { name: "Tallie"},
        { name: "Zack"}
      ]
    }
  ]
}

data[:users][0][:cats][0][:name] # => "Tallie"
data[:users][0][:dogs][0][:name] # NoMethodError: undefined method `[]' for nil:NilClass

data.dig(:users, 0, :cats, 0, :name) # => "Tallie"
data.dig(:users, 0, :dogs, 0, :name) # => nil

> "abcd".revrse
NoMethodError: undefined method `revrse' for "abcd":String
Did you mean?  reverse
               reverse!