Feature #22376: Undefine the allocator for Class

• Status: Open
• Assignee: -
• Target version: -

[jhawthorn (John Hawthorn)]

Uninitialized classes, created by Class.allocate, are a recurring source of bugs (most recently #22341). Every place that inspects a class's superclass chain has to check whether the class has been initialized, and it's easy to forget one.

I'd like to propose that we forbid Class.allocate, as we already do for several other core types (Proc, Method, UnboundMethod, Binding).

To do this we:

• Undefine the allocator for Class (rb_undef_alloc_func)
• Replace Class#initialize with a Class.new singleton method that allocates and initializes in one step.
• Define Class#dup and Class#clone so that copying a class still works

Class can't be subclassed, so I don't think we need to worry about calling initialize. The only place I found Class.allocate via gem-codesearch were copies of ruby/spec, so I don't think forbidding that will cause problems.

Before:

klass = Class.allocate
Class.new(klass) # 'Class#initialize': can't inherit uninitialized class (TypeError)
klass.superclass # 'Class#superclass': uninitialized class (TypeError)

After:

Class.allocate # undefined method 'allocate' for class Class (NoMethodError)
Class.instance_method(:allocate).bind_call(Class) # 'Class#allocate': allocator undefined for Class (TypeError)

PR: https://github.com/ruby/ruby/pull/18964

[jhawthorn (John Hawthorn)]

• Related to Feature #21852: New improved allocator function interface added

[jhawthorn (John Hawthorn)]

• Related to Feature #21963: A solution to completely avoid allocated-but-uninitialized objects added