Ruby Gotchas

and_or_1.rb

surprise = true and false # => surprise is true
surprise = true && false  # => surprise is false

and_or_2.rb

(surprise = true) and false # => surprise is true
surprise = (true && false)  # => surprise is false

bang_1.rb

'foo'.upcase! # => "FOO"
'FOO'.upcase! # => nil

bang_2.rb

@name.upcase! and render :show

bang_3.rb

@name.upcase!

render :show

eql.rb

1 == 1.0   # => true
1.eql? 1.0 # => false

exception.rb

class MyException < Exception
end

begin
  raise MyException
rescue
  puts 'Caught it!'
end

# MyException: MyException
#       from (irb):17
#       from /Users/karol/.rbenv/versions/2.1.0/bin/irb:11:in `<main>'

module_1.rb

MY_SCOPE = 'Global'

module Foo
  MY_SCOPE = 'Foo Module'

  class Bar
    def scope1
      puts MY_SCOPE
    end
  end
end

class Foo::Bar
  def scope2
    puts MY_SCOPE
  end
end

Foo::Bar.new.scope1 # => "Foo Module"
Foo::Bar.new.scope2 # => "Global"

module_2.rb

module Foo
  class Bar
  end
end

private_1.rb

class Foo
  private
  
  def self.bar
    puts 'Not-so-private class method called'
  end
end

Foo.bar # => "Not-so-private class method called"

private_2.rb

class Foo
  class << self
    private    
    
    def bar
      puts 'Class method called'
    end    
  end
  
  def self.baz
    puts 'Another class method called'
  end
  
  private_class_method :baz
end

Foo.bar # => NoMethodError: private method `bar' called for Foo:Class
Foo.baz # => NoMethodError: private method `baz' called for Foo:Class

setter_return_1.rb

class Foo
  def self.bar=(value)
    @foo = value

    return 'OK'
  end
end

Foo.bar = 3 # => 3

setter_return_2.rb

puts 'Assigned' if (Foo.bar = 3) == 'OK' # => nil

super.rb

class Foo
  def show
    puts 'Foo#show'
  end
end

class Bar < Foo
  def show(text)
    super
    puts text
  end
end

Bar.new.show('test') # ArgumentError: wrong number of arguments (1 for 0)