http://www.perlmonks.org?node_id=232957


in reply to my least favorite perl feature

Though this article deals with Lisp rather than Perl, the point is the same: equality (and its cousin copying) are rather difficult concepts, and it's rather impossible to get an operation involving them to automatically do the "right thing" all of the time, because there are many conflicting and incompatible yet individually perfectly valid notions of what the right thing is.