[ruby-core:75322] [Ruby trunk Bug#12337] inconsistency between Fixnum#coerce and Bignum#coerce

Issue #12337 has been updated by Benoit Daloze.


I had a question about Bignum#coerce in http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-core/75176.

I think it has limited value to have Bignum.coerce(Fixnum) or Fixnum.coerce(Bignum) return [Bignum, Bignum] instead of just the operands,
as it creates a Bignum in the Fixnum range, which is inconsistent with all other methods and might cause performance problems.
With #12005 this would be naturally the result with additionally no class distinction.

But indeed, Fixnum.coerce(Bignum) => [Float, Float] as currently is even worse probably (and shows how rarely {Bignum,Fixnum}#coerce are used in practice).

----------------------------------------
Bug #12337: inconsistency between Fixnum#coerce and Bignum#coerce
https://bugs.ruby-lang.org/issues/12337#change-58452

* Author: Akira Tanaka
* Status: Open
* Priority: Normal
* Assignee: 
* ruby -v: ruby 2.4.0dev (2016-05-01 trunk 54866) [x86_64-linux]
* Backport: 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN
----------------------------------------
I found 1.coerce(2.0) is [2.0, 1.0] but
(2**100).coerce(2.0) raises TypeError

```
% ./ruby -ve 'p 1.coerce(2.0)'       
ruby 2.4.0dev (2016-05-01 trunk 54866) [x86_64-linux]
[2.0, 1.0]
% ./ruby -ve 'p (2**100).coerce(2.0)'
ruby 2.4.0dev (2016-05-01 trunk 54866) [x86_64-linux]
-e:1:in `coerce': can't coerce Float to Bignum (TypeError)
	from -e:1:in `<main>'
```

This is a documented behavior.

```
% ri Bignum.coerce|cat
= Bignum.coerce

(from ruby core)
------------------------------------------------------------------------------
  big.coerce(numeric)  ->  array

------------------------------------------------------------------------------

Returns an array with both a numeric and a big represented as Bignum objects.

This is achieved by converting numeric to a Bignum.

A TypeError is raised if the numeric is not a Fixnum or Bignum type.

  (0x3FFFFFFFFFFFFFFF+1).coerce(42)   #=> [42, 4611686018427387904]
```

But I think this is bad bahavior.
Fixnum and Bignum should work seamlessly.

For example, this exposes the platform is 32-bit or 64-bit.
2**40 is Fixnum on 32-bit environment and Bignum on 64-bit environment.
So, (2**40).coerce(2.0) behaves differently: returns an array on 64-bit and
raises TypeError on 32-bit platform.

```
32bit-platform% ./ruby -ve 'p (2**40).coerce(2.0)'
ruby 2.4.0dev (2016-05-01 trunk 54866) [x86_64-linux]
[2.0, 1099511627776.0]

64bit-platform% ./ruby -ve 'p (2**40).coerce(2.0)'
ruby 2.4.0dev (2016-05-01 trunk 54864) [i686-linux]
-e:1:in `coerce': can't coerce Float to Bignum (TypeError)
	from -e:1:in `<main>'
```

I think the behavior of Bignum#coerce should be changed
to match Fixnum#coerce (actually defined at Numeric).


---Files--------------------------------
int-coerce.patch (2.37 KB)


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