Issue #15829 has been updated by nobu (Nobuyoshi Nakada).

Description updated

As it seems useful only when `condition` doesn't use the parameter `query`, it is questionable to me if it is generic enough to be a language feature.

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Feature #15829: Object#then_if(condition){}
https://bugs.ruby-lang.org/issues/15829#change-77979

* Author: foonlyboy (Eike Dierks)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
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I'd like to propose some sugar to Object#then

There should be `Object#then_if(condition, &block)`
 
The block should only be applied when the condition is true,
otherwise the object should be returned without applying the block.

Rationale:

I frequently use `Object#then` with Rails to extend queries like this:

```ruby
foo.then {|query|
  if(condition)
   query.where(zip:zap)
  else
   query
  end
}
```

by using the proposed `Object#then_if` the example could be simplified to:

```ruby
foo.then_if(condition) {|query|
   query.where(zip:zap)
}
```

I believe that this also applies to a lot of other use cases,
i.e. only applying some transformation if some condition is true,
but otherwise leaving the result untouched.















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