conditional chaining in ruby

Question

Is there a good way to chain methods conditionally in Ruby?

What I want to do functionally is

if a && b && c
 my_object.some_method_b         


        

Answer 1

Maybe your situation is more complicated than this, but why not:

my_object.method_a if a
my_object.method_b if b
my_object.method_c if c

Answer 2

You could put your methods into an arry and then execute everything in this array

l= []
l << :method_a if a
l << :method_b if b
l << :method_c if c

l.inject(object) { |obj, method| obj.send(method) }

Object#send executes the method with the given name. Enumerable#inject iterates over the array, while giving the block the last returned value and the current array item.

If you want your method to take arguments you could also do it this way

l= []
l << [:method_a, arg_a1, arg_a2] if a
l << [:method_b, arg_b1] if b
l << [:method_c, arg_c1, arg_c2, arg_c3] if c

l.inject(object) { |obj, method_and_args| obj.send(*method_and_args) }

Answer 3

I ended up writing the following:

class Object

  # A naïve Either implementation.
  # Allows for chainable conditions.
  # (a -> Bool), Symbol, Symbol, ...Any -> Any
  def either(pred, left, right, *args)

    cond = case pred
           when Symbol
             self.send(pred)
           when Proc
             pred.call
           else
             pred
           end

    if cond
      self.send right, *args
    else
      self.send left
    end
  end

  # The up-coming identity method...
  def itself
    self
  end
end


a = []
# => []
a.either(:empty?, :itself, :push, 1)
# => [1]
a.either(:empty?, :itself, :push, 1)
# => [1]
a.either(true, :itself, :push, 2)
# => [1, 2]

Answer 4

You can use tap:

my_object.tap{|o|o.method_a if a}.tap{|o|o.method_b if b}.tap{|o|o.method_c if c}

Answer 5

If you're using Rails, you can use #try. Instead of

foo ? (foo.bar ? foo.bar.baz : nil) : nil

write:

foo.try(:bar).try(:baz)

or, with arguments:

foo.try(:bar, arg: 3).try(:baz)

Not defined in vanilla ruby, but it isn't a lot of code.

What I wouldn't give for CoffeeScript's ?. operator.

Answer 6

I use this pattern:

class A
  def some_method_because_of_a
     ...
     return self
  end

  def some_method_because_of_b
     ...
     return self
  end
end

a = A.new
a.some_method_because_of_a().some_method_because_of_b()