Feature #15573
closedPermit zero step in Numeric#step and Range#step
Description
Numeric#step disallows zero in the 2nd argument, but it allows zero passed as the value of by:
keyword argument. I confirmed that this inconsistency exists since 2.3. I want to allow zero in the 2nd argument, too.
>> 1.step(10, by: 0) { break }
=> nil
>> 1.step(10, 0) { break }
Traceback (most recent call last):
5: from /Users/mrkn/.rbenv/versions/2.6.0/bin/irb:23:in `<main>'
4: from /Users/mrkn/.rbenv/versions/2.6.0/bin/irb:23:in `load'
3: from /Users/mrkn/.rbenv/versions/2.6.0/lib/ruby/gems/2.6.0/gems/irb-1.0.0/exe/irb:11:in `<top (required)>'
2: from (irb):5
1: from (irb):5:in `step'
ArgumentError (step can't be 0)
Moreover, Range#step disallows zero if a block is given. I want to relax also this restriction.
>> (1..10).step(0) { break }
Traceback (most recent call last):
6: from /Users/mrkn/.rbenv/versions/2.6.0/bin/irb:23:in `<main>'
5: from /Users/mrkn/.rbenv/versions/2.6.0/bin/irb:23:in `load'
4: from /Users/mrkn/.rbenv/versions/2.6.0/lib/ruby/gems/2.6.0/gems/irb-1.0.0/exe/irb:11:in `<top (required)>'
3: from (irb):6
2: from (irb):6:in `rescue in irb_binding'
1: from (irb):6:in `step'
ArgumentError (step can't be 0)
Updated by shyouhei (Shyouhei Urabe) almost 6 years ago
mrkn (Kenta Murata) wrote:
I want to relax also this restriction.
Tell us why? Consistency?
Updated by sawa (Tsuyoshi Sawada) almost 6 years ago
There is also inconsistency in that, without the block, 0
is allowed in these forms.
1.step(10, 0) # => ok
1.step(10, 0){} # => ArgumentError: step can't be 0
(1..10).step(0) # => ok
(1..10).step(0){} # => ArgumentError: step can't be 0
Since 0
can already sneak in, disallowing it just when the block is given makes it confusing. I agree that it should be relaxed.
Oops, sorry for the post if this was what mfkn has already pointed out.
Updated by shevegen (Robert A. Heiler) almost 6 years ago
I can't say in which way to change it but I think this is indeed surprising
behaviour and should be changed either way towards more consistency
if possible.
Updated by mrkn (Kenta Murata) over 5 years ago
Tell us why? Consistency?
The reason is that zero step allows when the block is not given.
>> 1.step(10, 0).each { break }
=> nil
irb(main):005:0> (1..10).step(0)
=> ((1..10).step(0))
>> (1..10).step(0).each { break }
=> nil
Updated by matz (Yukihiro Matsumoto) over 5 years ago
For this case, consistency matters. I thought it is better to raise an error on zero step. But @mrkn (Kenta Murata) can choose whatever behavior he believes right.
Matz.
Updated by mrkn (Kenta Murata) over 5 years ago
- Assignee changed from matz (Yukihiro Matsumoto) to mrkn (Kenta Murata)
Updated by fatkodima (Dima Fatko) about 4 years ago
Mathematically, it is allowed that step can be 0, but from practical stand point - this is an infinite loop waiting to be happen.
The original issue was about inconsistencies, so I decided to allow 0
for consistency (mainly because there is an ArithmeticSequence
which allows that) and deprecate raising an exception. Or we can rewrite the ArithmeticSequence
to raise and deprecate accepting 0 for all methods.
Updated by Dan0042 (Daniel DeLorme) about 4 years ago
What is the purpose of a zero step? I cannot understand why/how it would be used.
Updated by fatkodima (Dima Fatko) about 4 years ago
Dan0042 (Daniel DeLorme) wrote in #note-9:
What is the purpose of a zero step? I cannot understand why/how it would be used.
This is basically an infinite generator of the same number. I haven't real usecases for this also.
Updated by zverok (Victor Shepelev) about 4 years ago
What is the purpose of a zero step? I cannot understand why/how it would be used.
This is basically an infinite generator of the same number. I haven't real usecases for this also.
For edge cases like this, they typically emerge on dynamic calculation (and if the calculation is mathematically sound, they probably shouldn't raise). Like, I dunno, something like (intentionally vague)
(lower_threshold..upper_threshold).step(avg_object_size).take(5)
...will in edge case produce 5 copies of lower_threshold
, which, depending on application logic, might be a useful result. So, ArgumentError("Nobody on the tracker have seen a sense in this")
is probably undesireable.
Updated by fatkodima (Dima Fatko) about 4 years ago
Without take
(or simply if step
will have a block) this will be problematic.
But, agreed, good example.
Updated by Anonymous about 4 years ago
- Status changed from Open to Closed
Applied in changeset git|f754b422855131111092c0c147d744775cc4793f.
numeric.c, range.c: prohibit zero step
-
numeric.c: prohibit zero step in Numeric#step
-
range.c: prohibit zero step in Range#step
-
Fix ruby-spec
[Feature #15573]