[ruby-core:120571] [Ruby master Bug#20980] Range#size new TypeError vs semi-open ranges

Issue #20980 has been updated by mame (Yusuke Endoh).

Status changed from Open to Closed

The current behavior is intended. In principle, `#size` should return how many times `#each` will call a given block. (It could return nil as unknown.) Since beginless range does not respond to `#each`, it is now natural for `#size` to raise an exception. @naruse said he will try improving the document.

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Bug #20980: Range#size new TypeError vs semi-open ranges
https://bugs.ruby-lang.org/issues/20980#change-111395

* Author: zverok (Victor Shepelev)
* Status: Closed
* 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
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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:

```ruby
('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?..)



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