Bug #16467: Fetching a class variable with instance_eval fails with NameError

• Status: Rejected
• Assignee: -
• Target version: -
• ruby -v: ruby 2.7.0p0 (2019-12-25 revision 647ee6f091) [x86_64-darwin18]
• Backport: 2.5: UNKNOWN, 2.6: UNKNOWN

[barrettkingram (Barrett Ingram)]

Trying to fetch a class variable using instance_eval fails with uninitialized class variable @variable_name in Object (NameError).

Reproduction program:

class FooClass
  def initialize
    @foo = "foo"
    @@bar = "bar"
  end

  def get_bar
    @@bar
  end
end

foo = FooClass.new
puts foo.instance_eval("@foo") # prints "foo"
puts foo.get_bar # prints "bar"
puts foo.instance_eval("@@bar") # raises uninitialized class variable @@bar in Object (NameError)

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Rejected

Class variables need to be in the proper class context.
The following code raises a NameError too.

class FooClass::BarClass
  @@bar # NameError (uninitialized class variable @@bar in FooClass::BarClass)
end

You have to use class_eval.

foo.class.class_eval("@@bar")
# or
FooClass.class_eval("@@bar")