[ruby-core:114333] [Ruby master Bug#19795] attr_accessor leading to nil values for re-assignment
2 Aug
2023
2 Aug
'23
6:21 a.m.
Issue #19795 has been reported by francktrouillez (Franck Trouillez).
----------------------------------------
Bug #19795: attr_accessor leading to nil values for re-assignment
https://bugs.ruby-lang.org/issues/19795
* Author: francktrouillez (Franck Trouillez)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.2.2 (2023-03-30 revision e51014f9c0) [x86_64-linux]
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
### Steps to reproduce:
- Create a class with an `attr_accessor` for an instance variable
- Create an instance method that reassign this variable using the current value stored in
the variable
- Show that the variable is set to nil during the evaluation
Code snippet:
``` ruby
# attr_accessor_nil.rb
class A
attr_accessor :a
def initialize
@a = 1
end
def my_method
puts "a is '#{a.inspect}' of class '#{a.class}'"
a += 1 if a.positive? # use an integer method
end
end
instance = A.new
instance.my_method
# output:
#
# a is '1' of class 'Integer'
# attr_accessor_nil.rb:12:in `my_method': undefined method `positive?' for
nil:NilClass (NoMethodError)
#
# a += 1 if a.positive? # use an integer method
# ^^^^^^^^^^
# from attr_accessor_nil.rb:17:in `<main>'
```
### Expected behavior
`a += 1` should lead to `a` being equal to `1` at the end of the assignment, because `a`
was storing `0` previously, as shown by the `puts`. Am I being wrong expecting this
result?
### Actual behavior
`a += 1` raises an error about `a` being `nil` in the evaluation.
### Further investigation
I checked if it was coming from the "instance variable", or about the
"attr_accessor" by running the following snippet:
Code snippet:
```ruby
# attr_accessor_nil.rb
class A
attr_accessor :a
def initialize
@a = 0
end
def my_method
puts "a is '#{a.inspect}' of class '#{a.class}'"
@a += 1 # use the instance variable directly, instead of the accessor
end
end
instance = A.new
instance.my_method
# output:
#
# a is '1' of class 'Integer'
```
This snippet runs just fine, and no error is raised.
### System configuration
Ruby version : 3.2.2
--
https://bugs.ruby-lang.org/
2 Aug
2 Aug
6:42 a.m.
New subject: [ruby-core:114334] [Ruby master Bug#19795] attr_accessor leading to nil values for re-assignment
Issue #19795 has been updated by nobu (Nobuyoshi Nakada).
Status changed from Open to Closed
This is an assignment to the local variable, not the accessor.
```ruby
a += 1
```
You have to write:
```ruby
self.a += 1
```
----------------------------------------
Bug #19795: attr_accessor leading to nil values for re-assignment
https://bugs.ruby-lang.org/issues/19795#change-104038
* Author: francktrouillez (Franck Trouillez)
* Status: Closed
* Priority: Normal
* ruby -v: ruby 3.2.2 (2023-03-30 revision e51014f9c0) [x86_64-linux]
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
### Steps to reproduce:
- Create a class with an `attr_accessor` for an instance variable
- Create an instance method that reassign this variable using the current value stored in
the variable
- Show that the variable is set to nil during the evaluation
Code snippet:
``` ruby
# attr_accessor_nil.rb
class A
attr_accessor :a
def initialize
@a = 0
end
def my_method
puts "a is '#{a.inspect}' of class '#{a.class}'"
a += 1
end
end
instance = A.new
instance.my_method
# output:
#
# a is '0' of class 'Integer'
# attr_accessor_nil.rb:12:in `my_method': undefined method `+' for nil:NilClass
(NoMethodError)
#
# a += 1
# ^
# from attr_accessor_nil.rb:17:in `<main>'
```
### Expected behavior
`a += 1` should lead to `a` being equal to `1` at the end of the assignment, because `a`
was storing `0` previously, as shown by the `puts`. Am I being wrong expecting this
result?
### Actual behavior
`a += 1` raises an error about `a` being `nil` in the evaluation.
### Further investigation
I checked if it was coming from the "instance variable", or about the
"attr_accessor" by running the following snippet:
Code snippet:
```ruby
# attr_accessor_nil.rb
class A
attr_accessor :a
def initialize
@a = 0
end
def my_method
puts "a is '#{a.inspect}' of class '#{a.class}'"
@a += 1 # use the instance variable directly, instead of the accessor
end
end
instance = A.new
instance.my_method
# output:
#
# a is '0' of class 'Integer'
```
This snippet runs just fine, and no error is raised.
### System configuration
Ruby version : 3.2.2
--
https://bugs.ruby-lang.org/
6:55 a.m.
New subject: [ruby-core:114335] [Ruby master Bug#19795] attr_accessor leading to nil values for re-assignment
Issue #19795 has been updated by francktrouillez (Franck Trouillez).
I guess that it is a local variable, but is it the expected behavior?
As a developer, I expect that I can access `a` without the `self.a`.
Since the following code works as expected without `self`:
```ruby
# attr_accessor_nil.rb
class A
attr_accessor :a
def initialize
@a = 0
end
def my_method
puts "a is '#{a.inspect}' of class '#{a.class}'"
b = a + 1
a = 1
puts "b is '#{b.inspect}' of class '#{b.class}'"
puts "a is '#{a.inspect}' of class '#{a.class}'"
end
end
instance = A.new
instance.my_method
# output:
#
# a is '0' of class 'Integer'
# b is '1' of class 'Integer'
# a is '1' of class 'Integer'
```
I expect that the following works as well:
```ruby
# attr_accessor_nil.rb
class A
attr_accessor :a
def initialize
@a = 0
end
def my_method
puts "a is '#{a.inspect}' of class '#{a.class}'"
a = a + 1
end
end
instance = A.new
instance.my_method
# output:
#
# a is '0' of class 'Integer'
# Traceback (most recent call last):
# 1: from attr_accessor_nil.rb:17:in `<main>'
# attr_accessor_nil.rb:12:in `my_method': undefined method `+' for nil:NilClass
(NoMethodError)
```
Why can I access the instance variable (read and write) without the `self`, but as soon as
I try to re-assign it using the current value, it switches to a local variable? This is
something unexpected for me.
Is it the expected behavior for this? If so, is there a way of making this special case
clearer? Or am I being wrong thinking the behavior is unexpected?
----------------------------------------
Bug #19795: attr_accessor leading to nil values for re-assignment
https://bugs.ruby-lang.org/issues/19795#change-104039
* Author: francktrouillez (Franck Trouillez)
* Status: Closed
* Priority: Normal
* ruby -v: ruby 3.2.2 (2023-03-30 revision e51014f9c0) [x86_64-linux]
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
### Steps to reproduce:
- Create a class with an `attr_accessor` for an instance variable
- Create an instance method that reassign this variable using the current value stored in
the variable
- Show that the variable is set to nil during the evaluation
Code snippet:
``` ruby
# attr_accessor_nil.rb
class A
attr_accessor :a
def initialize
@a = 0
end
def my_method
puts "a is '#{a.inspect}' of class '#{a.class}'"
a += 1
end
end
instance = A.new
instance.my_method
# output:
#
# a is '0' of class 'Integer'
# attr_accessor_nil.rb:12:in `my_method': undefined method `+' for nil:NilClass
(NoMethodError)
#
# a += 1
# ^
# from attr_accessor_nil.rb:17:in `<main>'
```
### Expected behavior
`a += 1` should lead to `a` being equal to `1` at the end of the assignment, because `a`
was storing `0` previously, as shown by the `puts`. Am I being wrong expecting this
result?
### Actual behavior
`a += 1` raises an error about `a` being `nil` in the evaluation.
### Further investigation
I checked if it was coming from the "instance variable", or about the
"attr_accessor" by running the following snippet:
Code snippet:
```ruby
# attr_accessor_nil.rb
class A
attr_accessor :a
def initialize
@a = 0
end
def my_method
puts "a is '#{a.inspect}' of class '#{a.class}'"
@a += 1 # use the instance variable directly, instead of the accessor
end
end
instance = A.new
instance.my_method
# output:
#
# a is '0' of class 'Integer'
```
This snippet runs just fine, and no error is raised.
### System configuration
Ruby version : 3.2.2
--
https://bugs.ruby-lang.org/
7:32 a.m.
New subject: [ruby-core:114336] [Ruby master Bug#19795] attr_accessor leading to nil values for re-assignment
Issue #19795 has been updated by francktrouillez (Franck Trouillez).
I got it in the end thanks to a peer. I misunderstood wrongly how this was working:
Running the following snippet helped me understand:
```ruby
# attr_accessor_nil.rb
class A
attr_accessor :a
def initialize
@a = 0
end
def my_method
puts "a is '#{a.inspect}' of class '#{a.class}'"
b = a + 1
a = b
puts "b is '#{b.inspect}' of class '#{b.class}'"
puts "a is '#{a.inspect}' of class '#{a.class}'"
end
def my_method_2
puts "a is '#{a.inspect}' of class '#{a.class}'"
end
end
instance = A.new
instance.my_method
instance.my_method_2
# output:
#
# a is '0' of class 'Integer'
# b is '1' of class 'Integer'
# a is '1' of class 'Integer'
# a is '0' of class 'Integer'
```
So, we cannot modify the instance variable through the accessor directly. If it was, the
last `puts` should show `1`
Thanks for your help!
----------------------------------------
Bug #19795: attr_accessor leading to nil values for re-assignment
https://bugs.ruby-lang.org/issues/19795#change-104041
* Author: francktrouillez (Franck Trouillez)
* Status: Closed
* Priority: Normal
* ruby -v: ruby 3.2.2 (2023-03-30 revision e51014f9c0) [x86_64-linux]
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
### Steps to reproduce:
- Create a class with an `attr_accessor` for an instance variable
- Create an instance method that reassign this variable using the current value stored in
the variable
- Show that the variable is set to nil during the evaluation
Code snippet:
``` ruby
# attr_accessor_nil.rb
class A
attr_accessor :a
def initialize
@a = 0
end
def my_method
puts "a is '#{a.inspect}' of class '#{a.class}'"
a += 1
end
end
instance = A.new
instance.my_method
# output:
#
# a is '0' of class 'Integer'
# attr_accessor_nil.rb:12:in `my_method': undefined method `+' for nil:NilClass
(NoMethodError)
#
# a += 1
# ^
# from attr_accessor_nil.rb:17:in `<main>'
```
### Expected behavior
`a += 1` should lead to `a` being equal to `1` at the end of the assignment, because `a`
was storing `0` previously, as shown by the `puts`. Am I being wrong expecting this
result?
### Actual behavior
`a += 1` raises an error about `a` being `nil` in the evaluation.
### Further investigation
I checked if it was coming from the "instance variable", or about the
"attr_accessor" by running the following snippet:
Code snippet:
```ruby
# attr_accessor_nil.rb
class A
attr_accessor :a
def initialize
@a = 0
end
def my_method
puts "a is '#{a.inspect}' of class '#{a.class}'"
@a += 1 # use the instance variable directly, instead of the accessor
end
end
instance = A.new
instance.my_method
# output:
#
# a is '0' of class 'Integer'
```
This snippet runs just fine, and no error is raised.
### System configuration
Ruby version : 3.2.2
--
https://bugs.ruby-lang.org/
292
days inactive
292
days old
3 comments
2 participants
participants (2)
-
francktrouillez (Franck Trouillez) -
nobu (Nobuyoshi Nakada)