Issue #12901 has been updated by Benoit Daloze.


To come back to the main topic of this issue,
I think having some syntax support for a non-capturing lambda
can be a useful feature in Ruby, but should not be for performance reasons.
It should be a design tool.

If a lambda/proc does not use captured variables, there is no reason
for it to lookup parent scopes.  So there should not be any scope lookup overhead
if a lambda/proc does not capture variables.

What is the source of the overhead for calling lambdas on MRI?
Is it restoring the implicit state (self, cref, a pointer to the parent frame
in case #binding is called, etc) that must be restored? Some extra checks?

Kernel#binding applies to all kinds of lambdas/procs and
that affects how frames can be represented but it is mostly orthogonal
to this issue (methods also have to care about Kernel#binding).

----------------------------------------
Feature #12901: Anonymous functions without scope lookup overhead
https://bugs.ruby-lang.org/issues/12901#change-63301

* 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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