SystemStackError on Hash#eql? with mutally recursive hashes

[lopopolo]

$ irb
mirb - Embeddable Interactive Ruby Shell

> RUBY_VERSION
 => "3.0"
> RUBY_ENGINE
 => "mruby"
> a = {} ; b = {}
 => {}
> a.merge! self: a, other: b ; nil
 => nil
> b.merge! self: b, other: a ; nil
 => nil
> a.eql? b
stack level too deep (SystemStackError)

[matz]

It's mruby limitation. The recursive check requires memory, which can be very precious on mruby target platforms.
If you can think of memory-efficient implementation (like using the tortoise-and-hare algorithm), please tell me.

[matz]

FYI, CPython also gives up a recursive comparison.