[ruby-core:76571] [Ruby trunk Feature#12608] Proposal to replace unless in Ruby

Issue #12608 has been updated by Lucian Cancescu.


Thanks all for the replies. A few examples will obviously not cover everything to convince everyone. My examples were probably not the best but you get the idea, it happens a lot and it can so easily be changed.

However, I continue see so many wrong usages of unless that it makes me question whether its presence in the language is a good idea at all. I am sure I'm not the only one who has ever struggled to read a complicated unless/else structure. You can call it a poor design, but it's something that allows people to so easily shoot themselves in the foot. And they seem to enjoy doing it.

We have two things to achieve the same result, one (if) is positive and the other (unless) is negative. I think this brings the confusion.

I realize that my initial proposal has a very big impact and will probably be rejected.

However, I still believe we can improve the situation by not allowing unless to be used together with else.


----------------------------------------
Feature #12608: Proposal to replace unless in Ruby
https://bugs.ruby-lang.org/issues/12608#change-59798

* Author: Lucian Cancescu
* Status: Open
* Priority: Normal
* Assignee: 
----------------------------------------
Hi,

I would like to propose the replacement of the `unless` statement in Ruby. 

# Problem description:
Unless is complex and my arguments are:

* I often see in projects `unless ... else`:

~~~ ruby
unless user
  redirect_to_login
else 
  render_profile
end
~~~


* Using `unless` with conditionals makes it very hard to understand:

~~~ ruby
unless user || tenant
  user_and_tenant_are_present
end
~~~
Put an else to the conditional above and you can easily spend a few minutes to correctly understand what the code does.

Ruby is focuses on simplicity. I find both the examples above speaking against it. I have seen many Ruby projects, written by different people, and in most of them you see `unless` being abused in some way.

There is another aspect, when you see unless you have to keep a `not` in mind. The problem with that is that you have to negate all you read afterwards. You have to remove the negation when an else appears and you have to carefully read the negation with parenthesis in mind when `unless` contains boolean conditions. It's a huge complexity which can be avoided by simply using something else.

# Proposed solution:
How can we reduce the complexity? Other languages, for instance Swift, have introduced the `guard` [1] statement.

`guard` can replace `unless` in Ruby and the complex scenarios from above would become impossible:

Example 1 from above translates to:

~~~ ruby
guard user else
  return redirect_to_login
end
# do something with the user
render_profile
~~~

Example 2 from above translates to:

~~~ ruby
guard user && tenant else
  return user_or_tenant_missing
end
# do something with the user and the tenant
user_and_tenant_are_present
~~~

Not only the conditions become easier to read, but it reduces a lot the complexity of the code.

My suggestion is to add `guard` to the language and make it replace `unless`. What do you think?

Thanks,
Lucian

[1] Guard in Swift: https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/guard-statement



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