Issue #13237 has been reported by Marcus Stollsteimer.

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Bug #13237: Behavior for #dup and #clone on Rational/Complex/BigDecimal differs from Integer/Float
https://bugs.ruby-lang.org/issues/13237

* Author: Marcus Stollsteimer
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.4.0p0 (2016-12-24 revision 57164) [x86_64-linux]
* Backport: 2.2: UNKNOWN, 2.3: UNKNOWN, 2.4: UNKNOWN
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Since the implementation of feature #12979, #dup and #clone on Integer and Float do not raise a `TypeError` anymore, and silently return self. Rational and Complex still raise an exception.

I'm not sure whether this inconsistent behavior is intended or only an oversight. I guess all Numeric classes should behave in a similar way?

Additionally, what is the intention regarding the returned object for non-immediate numeric values, should they return self or a new object?
At the time being, BigDecimal (which already did allow #dup/#clone before the change) returns a new object, while Bignum integers return self.

Current behavior:

``` ruby
RUBY_VERSION  # => "2.4.0"

1.dup      # => 1
1.clone    # => 1
1.5.dup    # => 1.5
1.5.clone  # => 1.5

Rational(1).dup    rescue $!  # => #<TypeError: can't copy Rational>
Rational(1).clone  rescue $!  # => #<TypeError: can't copy Rational>
Complex(1).dup     rescue $!  # => #<TypeError: can't copy Complex>
Complex(1).clone   rescue $!  # => #<TypeError: can't copy Complex>

require "bigdecimal"
BigDecimal(1).dup    # => 0.1e1
BigDecimal(1).clone  # => 0.1e1

d = (1<<64)
[d.object_id, d.dup.object_id, d.clone.object_id]  # => [5134140, 5134140, 5134140]

d = BigDecimal(1)
[d.object_id, d.dup.object_id, d.clone.object_id]  # => [5133040, 5132900, 5132840]
```

Old behavior:

``` ruby
RUBY_VERSION  # => "2.3.3"

1.dup      rescue $!  # => #<TypeError: can't dup Fixnum>
1.clone    rescue $!  # => #<TypeError: can't clone Fixnum>
1.5.dup    rescue $!  # => #<TypeError: can't dup Float>
1.5.clone  rescue $!  # => #<TypeError: can't clone Float>

Rational(1).dup    rescue $!  # => #<TypeError: can't copy Rational>
Rational(1).clone  rescue $!  # => #<TypeError: can't copy Rational>
Complex(1).dup     rescue $!  # => #<TypeError: can't copy Complex>
Complex(1).clone   rescue $!  # => #<TypeError: can't copy Complex>

require "bigdecimal"
BigDecimal(1).dup    # => #<BigDecimal:101e270,'0.1E1',9(27)>
BigDecimal(1).clone  # => #<BigDecimal:101dfa0,'0.1E1',9(27)>
```



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