Issue #8237 has been updated by rosenfeld (Rodrigo Rosenfeld Rosas).


I really believe it would be better to isolate each wanted feature in a separate ticket instead of mixing several ideas in the same ticket. Also, I guess you should state clearly that a&&.b&&.c should mean (tmp1 = a; tmp1 && (tmp2 = tmp1.b); tmp2 && tmp2.c), meaning that each method should be evaluated just once in the chain.

Anyway, I'm -1 for this proposal (with the implementation above) because it doesn't make any sense to me to call any method on the "false" object in most real-world codes out there. I'm favorable to adding a shortcut syntax for chaining methods, but I believe it should check for "nil?" only. I don't have an opinion yet if it should abort the entire statement if a subexpression is nil, like CoffeeScript does, or simply replace the subexpression with "nil" and let the expression go on with the evaluation, like Groovy does.
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Feature #8237: Logical method chaining via inferred receiver
https://bugs.ruby-lang.org/issues/8237#change-38349

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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