[#99115] [Ruby master Bug#17023] How to prevent String memory to be relocated in ruby-ffi — larskanis@...
Issue #17023 has been reported by larskanis (Lars Kanis).
22 messages
2020/07/10
[#99375] [Ruby master Feature#17055] Allow suppressing uninitialized instance variable and method redefined verbose mode warnings — merch-redmine@...
Issue #17055 has been reported by jeremyevans0 (Jeremy Evans).
29 messages
2020/07/28
[#101207] [Ruby master Feature#17055] Allow suppressing uninitialized instance variable and method redefined verbose mode warnings
— merch-redmine@...
2020/12/02
Issue #17055 has been updated by jeremyevans0 (Jeremy Evans).
[#101231] Re: [Ruby master Feature#17055] Allow suppressing uninitialized instance variable and method redefined verbose mode warnings
— Austin Ziegler <halostatue@...>
2020/12/03
What does this mean?
[ruby-core:99190] [Ruby master Bug#14541] Class variables have broken semantics, let's fix them
From:
eregontp@...
Date:
2020-07-16 08:36:10 UTC
List:
ruby-core #99190
Issue #14541 has been updated by Eregon (Benoit Daloze).
Note that while setting a top-level immediately raises:
```
$ ruby -e '@@a=42'
-e:1:in `<main>': class variable access from toplevel (RuntimeError)
```
Overtaking a class variable only raises on read (because of how class variable lookup is done on MRI, always look all ancestors without caching):
```
$ ruby -e 'class C; end; class CC<C; @@a=:CC; end; class C; @@a=:C; end; p :OK'
:OK
$ ruby -e 'class C; end; class CC<C; @@a=:CC; end; class C; @@a=:C; end; class CC; p @@a; end'
-e:1:in `<class:CC>': class variable @@a of CC is overtaken by C (RuntimeError)
from -e:1:in `<main>'
```
----------------------------------------
Bug #14541: Class variables have broken semantics, let's fix them
https://bugs.ruby-lang.org/issues/14541#change-86570
* Author: Eregon (Benoit Daloze)
* Status: Closed
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
* ruby -v: ruby 2.6.0dev (2018-01-29 trunk 62091) [x86_64-linux]
* Backport: 2.3: UNKNOWN, 2.4: UNKNOWN, 2.5: UNKNOWN
----------------------------------------
Class variables have the weird semantics of being tied to the class hierarchy and being inherited between classes.
I think this is counter-intuitive, dangerous and basically nobody expects this behavior.
To illustrate that, we can break the tmpdir stdlib by defining a top-level class variable:
$ ruby -rtmpdir -e '$SAFE=1; @@systmpdir=42; p Dir.mktmpdir {}'
-e:1: warning: class variable access from toplevel
Traceback (most recent call last):
3: from -e:1:in `<main>'
2: from /home/eregon/prefix/ruby-trunk/lib/ruby/2.6.0/tmpdir.rb:86:in `mktmpdir'
1: from /home/eregon/prefix/ruby-trunk/lib/ruby/2.6.0/tmpdir.rb:125:in `create'
/home/eregon/prefix/ruby-trunk/lib/ruby/2.6.0/tmpdir.rb:125:in `join': no implicit conversion of Integer into String (TypeError)
Or even simpler in RubyGems:
$ ruby -e '@@all=42; p Gem.ruby_version'
-e:1: warning: class variable access from toplevel
Traceback (most recent call last):
3: from -e:1:in `<main>'
2: from /home/eregon/prefix/ruby-trunk/lib/ruby/2.6.0/rubygems.rb:984:in `ruby_version'
1: from /home/eregon/prefix/ruby-trunk/lib/ruby/2.6.0/rubygems/version.rb:199:in `new'
/home/eregon/prefix/ruby-trunk/lib/ruby/2.6.0/rubygems/version.rb:199:in `[]': no implicit conversion of String into Integer (TypeError)
So defining a class variable on Object removes class variables in all classes inheriting from Object.
Maybe @@systmpdir is not so prone to conflict, but how about @@identifier, @@context, @@locales, @@sequence, @@all, etc which are class variables of the standard library?
Moreover, class variables are extremely complex to implement correctly and very difficult to optimize due to the complex semantics.
In fact, none of JRuby, TruffleRuby, Rubinius and MRuby implement the "setting a class var on Object removes class vars in subclasses".
It seems all implementations but MRI print :foo twice here (instead of :foo :toplevel for MRI):
~~~ ruby
class Foo
@@cvar = :foo
def self.read
@@cvar
end
end
p Foo.read
@@cvar = :toplevel
p Foo.read
~~~
Is there any library actually taking advantage that class variables are inherited between classes? I would guess not or very few.
Therefore, I propose to give class variable intuitive semantics: no inheritance, they behave just like variables of that specific class, much like class-level instance variables (but separate for compatibility).
Another option is to remove them completely, but that's likely too hard for compatibility.
Thoughts?
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