Issue #11934 has been updated by Colin Fulton.


I agree with Chris: JRuby + Truffle showed that it is possible to have dynamic features without loosing performance. Philosophically I am reminded of Ruby's syntax. It is **really** hard to write a Ruby parser but even though that makes it really hard to make a Ruby parser, it also makes it easier for developers to write easy to read code.

A de-optimizing JIT compiler like the one JRuby + Truffle has is very hard (but possible) to write, but would make it much easier for developers to write higher performance code. The JIT compilation would make things run faster (usually). The de-optimizer would mean that if a developer needs performance they can make it less dynamic and would automatically get the higher performance that this flag would offer.

When it comes to Ruby I will always be in favor of a more complicated and harder to write runtime instead of making things harder on developers. Sorry runtime devs. ;-)

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Feature #11934: A feature to drop dynamics dynamically
https://bugs.ruby-lang.org/issues/11934#change-56990

* 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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