Issue #18285 has been updated by mame (Yusuke Endoh). I have created a PR based on @akr 's proposal. https://github.com/ruby/ruby/pull/6950 ``` 42.time #=> undefined method `time' for object Integer (NoMethodError) class Foo privatee #=> undefined local variable or method 'privatee' for class Foo (NoMethodError) end s = "" def s.foo = nil s.bar #=> undefined method `bar' for extended object String (NoMethodError) ``` I think we can almost agree to stop using `#inspect` in `NoMethodError#message`. Now, we need to decide the new message format. However, I think it is difficult to decide this through discussion and imagination because it is very much a matter of preference. So, how about trying @akr's proposal towards Ruby 3.3, after the release of Ruby 3.2? Let's evaluate how annoying (or not) the new error format would be for daily programming by those who uses master. Note that @akr is one of the most proven and trusted committers in the area of designing Ruby. I believe that his proposal is a good start. ---------------------------------------- Feature #18285: NoMethodError#message uses a lot of CPU/is really expensive to call https://bugs.ruby-lang.org/issues/18285#change-100699 * Author: ivoanjo (Ivo Anjo) * Status: Open * Priority: Normal ---------------------------------------- Hello there! I'm working at Datadog on the ddtrace gem -- https://github.com/DataDog/dd-trace-rb and we ran into this issue on one of our internal testing applications. I also blogged about this issue in <https://ivoanjo.me/blog/2021/11/01/nomethoderror-ruby-cost/>. ### Background While testing an application that threw a lot of `NoMethodError`s in a Rails controller (this was used for validation), we discovered that service performance was very much impacted when we were logging these exceptions. While investigating with a profiler, the performance impact was caused by calls to `NoMethodError#message`, because this Rails controller had a quite complex `#inspect` method, that was getting called every time we tried to get the `#message` from the exception. ### How to reproduce ```ruby require 'bundler/inline' gemfile do source 'https://rubygems.org' gem 'benchmark-ips' end puts RUBY_DESCRIPTION class GemInformation # ... def get_no_method_error method_does_not_exist rescue => e e end def get_runtime_error raise 'Another Error' rescue => e e end def inspect # <-- expensive method gets called when calling NoMethodError#message Gem::Specification._all.inspect end end NO_METHOD_ERROR_INSTANCE = GemInformation.new.get_no_method_error RUNTIME_ERROR_INSTANCE = GemInformation.new.get_runtime_error Benchmark.ips do |x| x.config(:time => 5, :warmup => 2) x.report("no method error message cost") { NO_METHOD_ERROR_INSTANCE.message } x.report("runtime error message cost") { RUNTIME_ERROR_INSTANCE.message } x.compare! end ``` ### Expectation and result Getting the `#message` from a `NoMethodError` should be no costly than getting it from any other exception. In reality: ``` ruby 3.0.2p107 (2021-07-07 revision 0db68f0233) [x86_64-linux] no method error message cost 115.390 (± 1.7%) i/s - 580.000 in 5.027822s runtime error message cost 6.938M (± 0.5%) i/s - 35.334M in 5.092617s Comparison: runtime error message cost: 6938381.6 i/s no method error message cost: 115.4 i/s - 60130.02x (± 0.00) slower ``` ### Suggested solutions 1. Do not call `#inspect` on the object on which the method was not found (see <https://github.com/ruby/ruby/blob/e0915ba67964d843832148aeca29a1f8244ca7b1/error.c#L1962>) 2. Cache result of calling `#message` after the first call. Ideally this should be done together with suggestion 1. -- https://bugs.ruby-lang.org/