ruby-core

Issue #12901 has been updated by Shyouhei Urabe.


Robert Mosolgo wrote:
> What about checking at the block level? I mean, could we check that:
> 
> - All local variable reads come from the block's local table 
> - There are no method calls on implicit receiver 
> 
> So, this could be optimized: 
> 
> ~~~ ruby
> lambda { |a, b| a + b }
> ~~~

Sorry, no.  You can look at outside scope from within the lambda's binding like this:

```
zsh % rbenv exec irb
irb(main):001:0> a = 1
=> 1
irb(main):002:0> b = lambda {|c, d| c + d }.binding
=> #<Binding:0x007fa672001160>
irb(main):003:0> b.local_variable_set(:a, 2)
=> 2
irb(main):004:0> a
=> 2
irb(main):005:0>
```

The lambda does not use variable `a`.  But still, you can see through the binding.

----------------------------------------
Feature #12901: Anonymous functions without scope lookup overhead
https://bugs.ruby-lang.org/issues/12901#change-63243

* 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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