Defines new_method as an alias of old_method.

One forwarder is defined per overload of old_method, reproducing that overload's parameter list verbatim — restrictions, defaults, keyword-only section and block argument included. So the alias is exactly as type-safe as what it aliases, and named arguments and blocks both work.

class Person
  getter name

  def initialize(@name)
  end

  alias_method full_name, name
end

person = Person.new "John"
person.name      # => "John"
person.full_name # => "John"

Copying the restrictions is what makes an alias safe to introduce next to an existing method of the same name inherited from elsewhere. An unrestricted def alias(*args) forwarder would sit closer in the ancestor chain than that inherited method and silently swallow every call to it; a restricted one only claims the argument types it actually handles, leaving the rest to resolve as before.

This macro was present in Crystal until commit 7c3239ee505e07544ec372839efed527801d210a.

Defines new_method as an alias of the immediately preceding method.

NOTE only use this when the preceding method has a single overload. @type.methods does not preserve source order once a name is overloaded, so "the last one" is not reliably the one written just above. Name the target explicitly with alias_method in that case.