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class_eval_vs_module_eval

🕹️ Dynamically Adding Methods with class_eval​

Use class_eval or module_eval to inject methods or constants at runtime. This approach is helpful in metaprogramming for DSLs or dynamic API wrappers.

class APIClient; end

APIClient.class_eval do
  def fetch(resource)
    "Fetching \\#{resource}"
  end
end

client = APIClient.new
puts client.fetch('users')
# => "Fetching users"