Project

General

Profile

Feature #18773

Updated by kddnewton (Kevin Newton) almost 2 years ago

Currently when you're pattern matching against a hash pattern, `deconstruct_keys` receives the keys that are being matched. This is really useful for computing expensive hashes. 

 However, when you're pattern matching against an array pattern, you don't receive any information. So if the array is expensive to compute (for instance loading an array of database records), you have no way to bail out. It would be useful to receive a range signifying how many records the pattern is specifying. It would be used like the following: 

 ```ruby 
 class ActiveRecord::Relation 
   def deconstruct(range) 
     (loaded? || range.cover?(count)) ? records : nil 
   end 
 end 
 ``` 

 It needs to be a range and not just a number to handle cases where `*` is used. You would use it like: 

 ```ruby 
 case Person.all 
 in [] 
   "No records" 
 in [person] 
   "Only #{person.name}" 
 else 
   "Multiple people" 
 end 
 ``` 

 In this way, you wouldn't have to load the whole thing into memory to check if it pattern matched. The patch is here: https://github.com/ruby/ruby/pull/5905.

Back