File::open and File.open

ruby-talk
1

What exactly is the difference between these?

:: and . are interchangeable for method calls (I think fully):
  irb(main):001:0> class Foo; attr_accessor :bar; end
  => nil
  irb(main):002:0> f = Foo.new
  => #<Foo:0x2c9abd8>
  irb(main):003:0> f::bar
  => nil
  irb(main):004:0> f::bar = 12
  => 12
  irb(main):005:0> f::bar
  => 12

"::" must be used for constant lookup:

  irb(main):001:0> class Foo; BAR = 12; end
  => 12
  irb(main):002:0> Foo::BAR
  => 12
  irb(main):003:0> Foo.BAR
  NoMethodError: undefined method `BAR' for Foo:Class
          from (irb):3

Most people (I believe) only use "::" for constants, and "." for all
method calls.

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From: Brad Tilley