Issue #11934 has been updated by Yusuke Endoh.


Eric, thank you for your comment.

> We already allow "freeze" on classes and modules; perhaps we perform
> some optimizations when they become frozen: perfect hashing,
> rehash/repack hashes for locality, reducing checks in bytecode, etc...

Is constant folding possible?  And method inlining?  They may be possible, but I guess the effect will be restricted.  To get the best of the optimizations, I think we need to freeze all classes and modules, including singleton classes.

Personally I don't want to recommend "freeze on classes/modules" because some people may use them blindly, like `"string".freeze`.  If it is widely used by default in many libraries for the purpose of performance improvement, Ruby's dynamics may be killed in effect.  Instead, switching on the whole VM looks a better choice to me.

In addition, it would be good to include "frozen string literal by default" into this mode.  It is impossible by "freeze on classes/modules".


> That should be both backwards and forwards compatible with
> old/parallel/future Ruby implementations and have better granularity
> instead of the whole VM.

Compatibility will be kept perfectly unless this feature is used.  In fact, this is one of the motivation of this proposal.  Recently, Ruby tends to sacrifice dynamics for performance improvement (such as frozen string literal by default).  I'd like to stop this and provide better "playing field" for users and developers who are interested in optimization.

-- 
Yusuke Endoh <mame / ruby-lang.org>

----------------------------------------
Feature #11934: A feature to drop dynamics dynamically
https://bugs.ruby-lang.org/issues/11934#change-55896

* Author: Yusuke Endoh
* Status: Feedback
* Priority: Normal
* Assignee: 
----------------------------------------
Ruby is a dynamic language.  Everything is possible in runtime.

So, how about a feature to prohibit some dynamic features in runtime?

~~~~
Foo = 1

RubyVM.drop_dynamics

Bar = 2        #=> cannot define new constant
Foo = 2        #=> cannot redefine a constant
def foo; end   #=> cannot define a method
class Baz; end #=> cannot create a new class
~~~~

Ruby's dynamic property greatly restricts performance.  However, it is a bad idea to limit Ruby's dynamics.  It is Ruby's identity, and is actually useful in some aspects such as debugging, daily-scripting, research, hobby-use, etc.

That being said, when a program is in production, we don't necessarily use the dynamic features at any time during execution.  Typically, they are used only in initialization of application, such as eval-for-DRY and monkey patching.  After the initialization is done, we can drop (some of) dynamic features in some situations.

Currently, when considering optimization of Ruby implementation, we (the core-team) must always care the possibility of redefinition of any built-in methods.  That is not sound.  This proposal gives us a "normal" condition for considering optimization.  We can easily apply a lot of optimizations, like constant folding and method inline expansion.  In addition, some advanced analyses like JIT/AOT compilation, type inference and whole program optimization will be applicable much more effectively.

--

It is arguable what features are prohibited.  IMO, it is relatively easy to drop the following features.

* (re)definition of constants
* (re)definition of methods (including singleton methods an aliases)
* (re)definition of classes/modules
* inclusion of modules

Aggressively, we may limit the following features.

* destructive modification of some kind of objects (such as making string literal frozen by default)
* some meta-programming features like `Object#send`
* `eval` and `instance_eval`
* addition of instance variables
* XXX <- feel free to add your unfavorite features

We should care about a trade-off between compatibility impact and optimization effect.

--

I'm half-joking, but half-serious.  I'm unsure if this is really a great idea, but surely better than just restricting Ruby specification by default (such as frozen string literal).  This may be a key feature towards Ruby3x3.  

What do you think?

-- 
Yusuke Endoh <mame / ruby-lang.org>



-- 
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