Ruby关键字参数

Question

I have the class. Method bar should accept argument foo with default value equal to @foo

class Foo
  attr_accessor :foo

  def bar(foo: foo)
    p foo
  end
end

In irb I execute:

> f = Foo.new
> f.foo = 'foobar'
> f.bar

For ruby 2.0 result is:

=> "foobar"

and for ruby 2.1:

=> nil

Who can explain this behavior?

Answer 1

Further research:

# (Ruby 2.1.0)
class Foo
  attr_accessor :foo

  def bar(foo: self.foo)
    foo
  end
end
f = Foo.new
f.foo = 'bar'
f.bar
# => "bar"

It seems Ruby 2.1.0 "initializes" local variable before evaluating the "right side" of this statement, so foo on the right side is treated as local variable and thus is evaluated to nil .

This experiment seems to confirm my hypothesis:

class Foo
  attr_accessor :foo
  def bar(foo: defined?(foo))
    foo
  end
end
# Ruby 2.0.0:
Foo.new.bar
# => "method"
# Ruby 2.1.0:
Foo.new.bar
# => "local-variable"