Why 'eval' in ruby is so slow? -


in ruby code below, 'eval' more 10 times slower 'def'.

i understand 'eval' needs parse string, suppose needs done once in example.

require "benchmark" gc.disable  eval "def run1; 10_000.times { #{"$a[5]\n" * 10_000} } end" def run2     10_000.times { "#{"$a[5]\n" * 10_000}" }  end  $a = [1,2,3,4,5,6,7,8,9,10]  puts "run1:" puts benchmark.measure { run1 }  puts "run2:" puts benchmark.measure { run2 }

you're not comparing equivalent functions. run1 ends being function $a[5]\n 10,000 times in single string, since string interpolation happens string built, before eval called. run2 runs 1 expect.

to see difference, toss ruby-prof mix:

require "benchmark" require 'ruby-prof'  gc.disable  eval "def run1; 10_000.times { #{"$a[5]\n" * 10_000} } end" def run2     10_000.times { "#{"$a[5]\n" * 10_000}" }  end  $a = [1,2,3,4,5,6,7,8,9,10]  puts "run1:" rubyprof.start puts benchmark.measure { run1 } result = rubyprof.stop printer = rubyprof::flatprinter.new(result) printer.print(stdout)  puts "run2:" rubyprof.start puts benchmark.measure { run2 } result = rubyprof.stop printer = rubyprof::flatprinter.new(result) printer.print(stdout)

edit: here results (i removed benchmark calls prune down basics)

(nick@monster)-(~/desktop) (523)⚡️ ruby derp.rb  run1: thread id: 2156059640 fiber id: 2163430960 total: 484.962207 sort by: self_time   %self      total      self      wait     child     calls  name 100.00    484.962   484.962     0.000     0.000        1   integer#times    0.00    484.962     0.000     0.000   484.962        1   global#[no method]    0.00    484.962     0.000     0.000   484.962        1   object#run1   * indicates recursively called methods run2: thread id: 2156059640 fiber id: 2163430960 total: 0.265188 sort by: self_time   %self      total      self      wait     child     calls  name  94.02      0.249     0.249     0.000     0.000    10000   string#*    5.98      0.265     0.016     0.000     0.249        1   integer#times    0.01      0.265     0.000     0.000     0.265        1   global#[no method]    0.00      0.265     0.000     0.000     0.265        1   object#run2   * indicates recursively called methods

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