在看别人的源码是，发现这样一句 path = ::File.expand_path 双冒号后面的我能理解，唯独是为什么双冒号前面可以不用加任何东西？？ 求各位帮忙解答下！谢谢！
Probe
#5
2013年02月02日
有个 Ruby 教程 Koans Test 里提过这个用法
require "test/unit"
class AboutScope < Test::Unit::TestCase
# ---------
class String
end
def test_bare_bones_class_names_assume_the_current_scope
assert_equal true, AboutScope::String == String
end
def test_nested_string_is_not_the_same_as_the_system_string
assert_equal false, String == "HI".class
end
def test_use_the_prefix_scope_operator_to_force_the_global_scope
assert_equal true, ::String == "HI".class
end
# ---------
PI = 3.1416
def test_constants_are_defined_with_an_initial_uppercase_letter
assert_equal AboutScope::PI, PI
end
# ---------
MyString = ::String
def test_class_names_are_just_constants
assert_equal true, MyString == ::String
assert_equal true, MyString == "HI".class
end
def test_constants_can_be_looked_up_explicitly
assert_equal true, PI == AboutScope.const_get("PI")
assert_equal true, MyString == AboutScope.const_get("MyString")
end
end
