From: "trans (SYSTEM ERROR)" <redmine@...>
Date: 2013-04-09T05:57:45+09:00
Subject: [ruby-core:54119] [ruby-trunk - Feature #8237] Logical method chaining via inferred receiver


Issue #8237 has been updated by trans (SYSTEM ERROR).


=begin
As long as you always "resolve" it should be okay. This is untested, but it's going to be something along the lines of:

    class AndAnd < BasicObject
      def initialize(receiver)
        @receiver = receiver
        @calls = []
      end
      def method_missing(s, *a, &b)
        @calls << [s, a, b]
        self
      end
      def resolve
        @calls.inject(@receiver) do |r, (s, a, b)|
         x = r.send(s, *a, &b)
         break nil if x.nil?
         x
      end
    end

    def trying
      AndAnd.new(self)
    end

Btw, `_?` isn't half bad. I wonder if it could just support `?`:

    user.?.profile.?.website.?.thumbnail

Or via "trying":

    user.?.profile.website.thumbnail.!

=end

----------------------------------------
Feature #8237: Logical method chaining via inferred receiver
https://bugs.ruby-lang.org/issues/8237#change-38372

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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