[ruby-core:113916] [Ruby master Bug#19733] Kernel#Rational does not accept prefix 0

Issue #19733 has been updated by sawa (Tsuyoshi Sawada).


@mame It seems that you were not aware of the fact that the documentation is wrong. And I hope you share with me the idea that we want the documentation to be correct. I think the reason why the documentation was wrong, and why you have not noticed it, is either because the specification is ad hoc or it was not implemented in the way it was intended. I believe this has to be solved in some way.

I can say that the current behavior is counter-intuitive. Even though `Integer` class is not a subclass of `Rational` class, coercion relation indicates that whatever can be interpreted as an `Integer` can be interpreted as a `Rational` but not vice versa. And I think people would normally expect whatever is interpretable by `Kernel#Integer` is interpretable by `Kernel#Rational`.

A use case that I can think of where this becomes relevant is an arithmetic program in which some string (from user input or from some data) is attempted to be interpreted using methods like `Kernel#Rational` or `Kernel#Integer` one after another (avoiding the use of methods like `eval` in fear of malicious code). Such program may attempt interpretation of a string by `Kernel#Rational`, and if it succeeds, go on to attempt interpretation by `Kernel#Integer` to see if the interpretation can be further narrowed down. However, if a non-decimal integer string is passed to `Kernel#Rational` and an error is raised, such program would give up attempting interpretation by `Kernel#Integer`, even though it would succeed, and that input string would be thrown away.


Even more strange is the fact that, in case of hexadecimal `0x` (but not with other `0` prefixes), it becomes interpretable by `Kernel#Float` again. This is a real mess.

```ruby
Integer("0x10") # => 2
Rational("0x10") # !> ArgumentError
Float("0x10") # => 10.0
```


----------------------------------------
Bug #19733: Kernel#Rational does not accept prefix 0
https://bugs.ruby-lang.org/issues/19733#change-103568

* Author: sawa (Tsuyoshi Sawada)
* Status: Feedback
* Priority: Normal
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
`Integer` and `Rational` literals accept prefix `0`. There is no difference in this respect.

```ruby
0b10 # => 2
0b10r # => (2/1)
```

However, when it comes to `Kernel#Integer` and `Kernel#Rational`, the former accepts prefix `0` while the latter does not. This is confusing. And as I do not see any reason they should behave differently, I think it is a bug. 

```ruby
Integer("0b10") # => 2
Rational("0b10") # !> ArgumentError
```



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