Compiling...

bench.rb

require "benchmark/ips"

HASH = { :foo => 1, :bar => 2 }

def hc
  {
    :foo => HASH.fetch(:foo),
    :bar => HASH.fetch(:bar),
  }
end

def dyn
  HASH.each_with_object({}) do |(key, value), result|
    result[key] = value
  end
end

def compile!
  content = HASH.map do |key, value|
    "#{key.inspect} => HASH.fetch(#{key.inspect}),"
  end.join(" ")

  body = "def compiled; { #{content} }; end"
  puts body
  eval body
end

compile!

p compiled
p dyn
p hc

Benchmark.ips do |x|
  x.report "hash" do
    dyn
  end

  x.report "hc" do
    hc
  end

  x.report "compiled" do
    compiled
  end

  x.compare!
end

results.txt

def compiled; { :foo => HASH.fetch(:foo), :bar => HASH.fetch(:bar), }; end
{:foo=>1, :bar=>2}
{:foo=>1, :bar=>2}
{:foo=>1, :bar=>2}
Calculating -------------------------------------
                hash    28.130k i/100ms
                  hc    45.333k i/100ms
            compiled    46.710k i/100ms
-------------------------------------------------
                hash    423.640k (± 6.0%) i/s -      2.110M
                  hc    869.989k (± 5.9%) i/s -      4.352M
            compiled    915.810k (± 5.5%) i/s -      4.578M

Comparison:
            compiled:   915810.3 i/s
                  hc:   869988.7 i/s - 1.05x slower
                hash:   423640.1 i/s - 2.16x slower