如何在Ruby / Rails中清晰定义“反义词”或“相反”方法？

Question

I'm pretty often defining methods and their antonyms in the code I'm writing, as in:

def happy?
  @happiness > 3
end

def sad?
  !happy?
end

Which is fine, but I'm a little surprised that Ruby or ActiveSupport doesn't give me something like:

def happy?
  @happiness > 3
end

alias_opposite :sad? :happy?

Or am I just looking in the wrong place?

Answer 1

There is no such method in popular libraries, but there is how this could be implemented

class Module
  def alias_opposite(a, b)
    define_method(a) { !self.send(b) }
  end
end

Usage

class A < Struct.new(:happiness)
  def happy?
    happiness > 3
  end

  alias_opposite :sad?, :happy?
end

p A.new(1).sad? # => true
p A.new(5).sad? # => false

Answer 2

I suspect this pattern is not as common in ruby because the unless keyword often does the trick:

# ...
clap_your_hands if happy?
stomp_your_feet unless happy?
# ...

Of course, its simple to roll your own:

module Antonymator
  def define_antonym(as, of)
    define_method(as.to_sym) do |*args|
      return !(send(of.to_sym, *args))
    end
  end
end

# Usage Example
class AreThey
  extend Antonymator
  define_antonym :uneql?, :eql?
  define_antonym :nonconsecutive?, :consecutive?
  def eql?(a, b)
    a == b
  end
  def consecutive?(a, b)
    a.next == b
  end
end

are_they = AreThey.new
puts are_they.uneql? 1, 2           # true
puts are_they.nonconsecutive? 1, 2  # false

Answer 3

If your methods return a Boolean, you can always include the positive method in the negative method.

def drinking_age?(age)
  age > @restricted_age
end

def not_drinking_age?(age)
  !drinking_age?(age)
end

@restricted_age = 20

Hope that helps.

I guess it depends on what 'opposite' means in the context.