From: Edvard Majakari <edvard.majakari@...>
Date: 2011-11-23T22:18:08+09:00
Subject: [ruby-core:41250] [ruby-trunk - Feature #5662] inject-accumulate, or Haskell's mapAccum*


Issue #5662 has been updated by Edvard Majakari.


Ok.. I'll give real example to show what is typical use case for us:

hash = MyDatabaseObject.get_all.infuse({}) { |h, r| h[normalize_db_key(r.id, r.name)] = r }

after that, code can quickly access any record by id and name saying

obj = hash[normalize_db_key(myid, myname)]
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Feature #5662: inject-accumulate, or Haskell's mapAccum*
http://redmine.ruby-lang.org/issues/5662

Author: Edvard Majakari
Status: Open
Priority: Normal
Assignee: 
Category: 
Target version: 


with Ruby, we often use this idiom to build a hash out of something:

new_hash = enum.inject({}) { |h, thing| h[compute_key(thing) = compute_value(thing)]; h }

while that last h is very easy to add, it is also easy to forget and feels logically not very injectish thing to do. I'd propose this we call 'infuse' in our project:

module Enumerable
  # like inject, but returns accumulator instead. Instead of writing
  #   [1, 2].inject({}) {|h, i| h[i] = 2*i; h }
  # just say
  #   [1, 2].infuse({}) {|h, i| h[i] = 2*i } # -> {1 => 2, 2 => 4}
  def infuse(init, &block)
    inject(init) { |acc, i| block.call(acc, i); acc }
  end
end

Eg. [1, 2].infuse({}) { |a, i| a[i] = 2*i } #  => {1 => 2, 2 => 4}

Instead of infuse, maybe inject_accum or inject_acc would be more rubyish method name.


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