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Bug #7395

closed

Negative numbers can't be primes by definition

Added by zzak (zzak _) about 12 years ago. Updated over 10 years ago.

Status:
Closed
Target version:
ruby -v:
2.0.0
Backport:
[ruby-core:49558]

Description

from github:
https://github.com/ruby/ruby/pull/187

By definition, a prime number can be a positive integer greater than 1.

http://mathworld.wolfram.com/PrimeNumber.html


Files

prime_refute_negative_numbers.patch (1.16 KB) prime_refute_negative_numbers.patch zzak (zzak _), 11/19/2012 12:40 PM

Updated by usa (Usaku NAKAMURA) almost 12 years ago

  • Status changed from Open to Assigned

Updated by ko1 (Koichi Sasada) almost 12 years ago

  • Subject changed from Negative numbers can't be primes by definition to Negative numbers can't be primes by definition
  • Target version changed from 2.0.0 to 2.1.0

Updated by hsbt (Hiroshi SHIBATA) almost 11 years ago

  • Target version changed from 2.1.0 to 2.2.0

Updated by ayumin (Ayumu AIZAWA) over 10 years ago

  • Status changed from Assigned to Closed
  • % Done changed from 0 to 100

Applied in changeset r45878.


  • lib/prime.rb (Prime#prime?): negative numbers can't be primes
    by definition. reported by Ivan Kataitsev. [Bug #7395]
  • test/test_prime.rb: add test.

Updated by hsbt (Hiroshi SHIBATA) over 10 years ago

ayumin

this issue seems incompatible changes. it should be add NEWS.

Updated by mame (Yusuke Endoh) over 10 years ago

  • Status changed from Closed to Assigned

Read the rdoc carefully:

Returns true if +self+ is a prime number, false for a composite.

By definition, a composite number can be also a positive integer greater than 1.

http://mathworld.wolfram.com/CompositeNumber.html

Thus,

1.prime? #=> false
0.prime? #=> false
(-1).prime? #=> false

looks all buggy (or undefined behavior) to me.
If we can change the spec, it would be good to raise an exception, return nil, or at least update the rdoc.
Anyway, the maintainer (Yugui) should treat this, I think.

--
Yusuke Endoh

Updated by ayumin (Ayumu AIZAWA) over 10 years ago

Endo-san

Your opinion seems right.

IMHO, I think Rdoc should be updated.
This method should evaluate the number is prime number or not.
It should not refer the number is composite number or not.

We may have to confirm Yugui's intention anyway.
Luckily I'm going to meet her on Wed, so I will ask her about this issue.

Shibata-san
I will add information to NEWS, once change was accepted by Yugui.

Updated by ayumin (Ayumu AIZAWA) over 10 years ago

  • Status changed from Assigned to Closed

Applied in changeset r46061.


add information of incompatibility about Prime.prime? [Bug #7395]

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