Issue #12901 has been updated by Shyouhei Urabe.


Benoit Daloze wrote:
> > now, should what be visible from the obtained binding?  Should we re-calculate the optimized-out variables?
> 
> I assume you mean a binding via Kernel#binding.
> I think that's the general contract of deoptimization: it must not be observable from the user.
> So at the deoptimization point, the current computations must be stored in a real frame,
> or be recomputed if they are side-effect free and the deoptimization implements that.

This (recomputation) sounds practically very difficult to me, if not impossible.  Much easier to avoid optimization at all when binding is used.

> If it is a Proc#binding, then it only captures variables defined outside the Proc,
> so variables only defined inside the Proc are not visible to that.
> With the technique I mentioned, writes to captured variables can
> only be optimized out if the surrounding scope is compiled as well.

OK, I see. I confused Kernel#binding and Proc#binding.  Thank you.

----------------------------------------
Feature #12901: Anonymous functions without scope lookup overhead
https://bugs.ruby-lang.org/issues/12901#change-63284

* Author: Richard Schneeman
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
Right now if you are writing performance sensitive code you can get a performance bump by not using anonymous functions (procs, lambdas, blocks) due to the scope lookup overhead.

https://twitter.com/apotonick/status/791167782532493312?lang=en

I would like to be able to create an anonymous function and specify I don't need it to perform the lookup when called.

I am thinking that this code:

~~~
Proc.new(scope: false) {|var| puts var }
~~~

Would be the equivalent of 

~~~
def anon(var)
  puts var
end
~~~

If you call it while trying to access something from outside of the scope it would error

~~~
var = "hello"
Proc.new(scope: false) { puts var }.call
# => NameError: undefined local variable or method `var' for main:Object
~~~

An example of a case where this could be used is found in https://github.com/rails/sprockets/pull/417. In this case we are getting rid of anonymous functions in favor of a method created with refinements. This solution works but it was not an obvious optimization. It would be convenient to have a syntax for defining anonymous functions that do not need access to caller scope.






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