Issue #8237 has been updated by boris_stitnicky (Boris Stitnicky).


> And the pattern isn't a && a.b && a.b.c, but (a.nil ? nil : (a.b.nil? ? nil : a.b.c)).

class NullObject # let's define null object
  def method_missing sym, *a, &b; self end
  def to_s; "null" end
end
class Integer # let's patch Integer with #b, #c methods
  def b; self + 1 end
  def c; self + 10 end
end
# let's define function that expects a number, and returns it unchanged
# if it is bigger than 42, otherwise returning a NullObject.
classify = lambda { |arg| arg > 42 ? arg : NullObject.new }
# and a function that applies #b and #c boldly to its argument
f = lambda { |arg| arg.b.c }
# and their composition
l = lambda { |arg| f.( classify.( arg ) ) }
# the point is, that null object pattern allows smooth handling of bold
# message passing without fear whether the object is "present" or "absent":
l.( 42 )
#=> null
l.( 43 )
#=> 54

Thus "shall we support try before do" question becomes "shall we support null object more".

l.( 32 ) + 10
#=> null
l.( l.( 2 ) ** 64 - 1 ) )
#=> null

----------------------------------------
Feature #8237: Logical method chaining via inferred receiver
https://bugs.ruby-lang.org/issues/8237#change-38813

Author: wardrop (Tom Wardrop)
Status: Open
Priority: Normal
Assignee: 
Category: 
Target version: 


=begin
This is a feature suggestion that was raised while discussing issue #8191. The feature suggestion is to introduce some form of logical method chaining to address this reasonably common pattern:

    user && user.profile && user.profile.website && user.profile.website.thumbnail

It would be reasonably trivial to shorten this to:

    user && .profile && .website && .thumbnail

The implementation I propose would be for Ruby to allow an inferred receiver; the dot prefix would be the syntax for this. The inferred receiver would resolve to the result of the last expression in the current scope. For illustrative purposes, the following would work under this proposal:

    "some string"
    puts .upcase #=> SOME STRING

Another example:

    puts .upcase if obj.success_message || obj.error_message

    # Instead of...

    message = (obj.success_message || obj.error_message)
    puts message.upcase if message

This can also potentially provide an alternative option in syntactically awkward scenario's, such as dealing with the return value of an if statement or a catch block, avoiding the need for temporary variable assignment:

    catch :halt do
      # Do something
    end

    if .nil?
       log.info "Request was halted" 
       response.body = "Sorry, but your request could not be completed"
    end

The logical chaining scenario is the main use case however. I just wanted to demonstrate how the proposed implementation could also be used in other creative ways.

=end


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