I'm not sure, but I think your counterexample is meant to show you can't replace `Array#pop`. However, that's not what you show -- you show that irb depends on

I'm not sure, but I think your counterexample is meant to show you can't replace `Array#pop`. However, that's not what you show -- you show that irb depends on `Array#pop` for its normal usage. Consider: $ ruby -e "class Array; def pop; self.first; end; end; puts [1,2,3].pop" 1