Bug #20980: Range#size new TypeError vs semi-open ranges

• Status: Open
• Assignee: -
• Target version: -
• ruby -v: ruby 3.4.0dev (2024-12-24T14:40:12Z master 07e89bde46) +PRISM [x86_64-linux]
• Backport: 3.1: DONTNEED, 3.2: DONTNEED, 3.3: DONTNEED

[zverok (Victor Shepelev)]

Since #18984, Range#size throws TypeError if the begin is not iterable (doesn't respond to #succ). It produces one small inconvenience compared to 3.3:

('a'..).size #=> nil
(..'a').size 
# 3.3: nil
# 3.4: can't iterate from NilClass (TypeError) -- well, probably makes sense

# BUT:
(3..).size #=> Infinity -- cool!
(..3).size 
# 3.3: Infinity -- reasonable?
# 3.4: can't iterate from NilClass (TypeError) -- worse?

I believe that while 3.4's behavior is explainable, 3.3's one has better DX.

(Obviously too late to change before the release, but maybe might be considered for some patch version or Ruby 3.5?..)