to_proc hack to access hash

class Array
  def to_proc
    ->(h) { length == 1 ? h[first] : h.values_at(*self) }
  end
end

[
  { name: "Ruby", "age" => 21 }, { name: "Common Lisp", "age" => 56 }
].map(&[:name, "age"])

# => [["Ruby", 21], ["Common Lisp", 56]]

But it is about 2.7 times slower than built-in way of doing this:

require 'benchmark/ips'

class Array
  def to_proc
    ->(h) { length == 1 ? h[first] : h.values_at(*self) }
  end
end

LANGUAGE_AND_AGE = [
  { name: "Ruby", "age" => 21 }, { name: "Common Lisp", "age" => 56 }
]

def built_in
  LANGUAGE_AND_AGE.map { |h| [h[:name], h['age']] }
end

def to_proc_hack
  LANGUAGE_AND_AGE.map(&[:name, "age"])
end

Benchmark.ips do |x|
  x.report('built_in')     { built_in }
  x.report('to_proc_hack') { to_proc_hack }
  x.compare!
end

$ ruby -v to-proc-hack.rb
ruby 2.2.0preview1 (2014-09-17 trunk 47616) [x86_64-darwin13]

Calculating -------------------------------------
            built_in     88340 i/100ms
        to_proc_hack     47669 i/100ms
-------------------------------------------------
            built_in  1806140.9 (±6.2%) i/s -    9010680 in   5.009917s
        to_proc_hack   665738.9 (±4.9%) i/s -    3336830 in   5.024990s

Comparison:
            built_in:  1806140.9 i/s
        to_proc_hack:   665738.9 i/s - 2.71x slower

Source: Array#to_proc for hash access - The Pug Automatic