- ruby helpers for method chaining


methodchain - ruby helpers for method chaining: chain, tap, then, else, and, or

Easy ways to navigate around nil without creating local variables.

Initial blog post describing previous ideas:

Author and License

Copyright (c) 2008 Greg Weber, Licensed under the MIT license


#then and #else

old way

              person = nil
              name = person ? : nil

new way

              name = person.then {|p|}
              # or
              name = person.then {name}

not a huge savings. But sometimes the person variable is actually a function call, and then we must save it in a variable first.

old way

              def find(*args)
                # do some expensive database queries
              person = find(:first)
              @phone = person &&   # => nil

new way

              @phone = find(:first).then {phone}   # => nil

We have reduced a line of code and removed a local variable. #else is the opposite of then, and the two methods can be used together

              'a'.then{'b'} #=> 'b'
              nil.then{'b'}.else{'c'} #=> 'c'

message sending

The normal conditional for #then and #else is self

              if self # inside MethodChain#then
                # evaluate block

#then and #else allow message sending as the conditional. See more examples of message sending with the MethodChain#chain examples below

              "not empty".then(:empty?) {"N/A"} # => "not empty"
                       "".then(:empty?) {"N/A"} # => "N/A"

#and, #or

old way

Return a default value or the original value depending on whether multiple conditions are met

              Person = )
              blank ='') # or {:phone => nil}
     && (not ? : "N/A" # => "N/A"
              p ='123')
     && (not ? : "N/A" # => "123"

new way

     {not empty?} || "N/A" # => "N/A"
     {not empty?} || "N/A" # => "123"


if you don‘t already know about this method, look it up on the net. The tap included here allows message sending.

old way

              arr = [1]
              arr.compact! # => nil
              arr.first # => 1

normal #tap (still valid)

              [1].tap {|arr| arr.compact!}.first # => 1

new #tap

              [1].tap(:compact!).first # => 1

normal #tap (still valid)

              [1].tap {|arr| arr.compact!}.tap {|arr| arr * 2}.first # => 1

new #tap

              [1].tap( :compact!, [:*, 2] ).first # => 1

You can also pass Procs as arguments

              [1].tap( :compact!, lambda{|arr| arr * 2} ).first # => 1


chain is like tap, but instead of always returning self, it will return the result of the method call.

              [1].chain(:first) == [1].first

But there is an important difference- chain guards against certain results (by default it guards against nil and false)

old way

              customer = nil
              customer && customer.order &&

new way

              customer.chain(:order, :id)

note that this is equivalent to

              customer.then {order}.then {id}

#chain - Custom guards, multiple arguments, and Procs

old way - guarding against zero

              value = 0
              result = if value == 0 then value else
                tmp = value.abs
                if tmp == 0 then tmp else
                  tmp * 20
              result # => 0

new way

              value.chain(:abs, [:*, 20]) {|s| s == 0 }   # => 0

Procs can be used, so this is equivalent to

              value.chain(:abs, lambda {|n| n * 20 }) {|s| s == 0 } # => 0


              require 'rubygems'

import all MethodChain methods into Object

              require 'methodchain'

selectively import MethodChain methods

              require 'methodchain/not-included'

You can then include methodchain into selected classes, or you can use the module-import gem to include only certain methods

              gem install module-import
              require 'module-import'
              class Object
                import MethodChain, :chain  # I only want Object#chain

import will still load all the private methods from the module:

  • yield_or_eval
  • send_as_function
  • send_as_functions


There are no proxy objects and no use of method_missing- these are simply function calls, so it should be fast.

private methods:

  • yield_or_eval: allows the two different block forms {|p|} and {name}, where the first form yields self and the second form is called using instance_eval.
  • send_as_function: allows symbols and arrays to be sent as messages, and calls yield_or_eval on Proc arguments
  • send_as_functions:

    def send_arguments_as_functions *args

                  args.each {|arg| send_as_function arg}



gem install methodchain




git clone git://


RDoc documentation

included with gem