From: "joel@... (Joel Drapper) via ruby-core" <ruby-core@...>
Date: 2023-03-08T12:04:59+00:00
Subject: [ruby-core:112741] [Ruby master Feature#19484] Calling `binding` on a C-level proc raises an `ArgumentError`

Issue #19484 has been reported by joel@drapper.me (Joel Drapper).



----------------------------------------

Feature #19484: Calling `binding` on a C-level proc raises an `ArgumentError`

https://bugs.ruby-lang.org/issues/19484



* Author: joel@drapper.me (Joel Drapper)

* Status: Open

* Priority: Normal

----------------------------------------

Calling `binding` on a C-level proc (from `&:symbol`) raises an `ArgumentError`, "Can't create Binding from C level Proc" but there is no way to tell if a given proc is a C-level proc before calling `binding` on it. It���s possible to rescue this error, but rescuing an exception is slow.



Given that a C-level proc doesn't have a binding, would it make more sense to respond to `binding` with `nil` rather than raise an error? That would allow us to, for example, look up the receiver and fall back to self, e.g. `block.binding&.receiver || self`.



Alternatively, it would be useful to be able to check whether a given proc is a C-Level proc using something like this.



```ruby

case block

when CProc

  block.call(self)

else

  block.call

end

```



An example use case is an interface that takes a hash of conditions and tokens. If the condition is valid, we do something with the token. Otherwise, we ignore it.



```ruby

some_interface(-> { true } => "foo", -> { false } => "bar" )

```



With literal Procs, it makes sense to call them and check their truthiness.



```ruby

def some_interface(**conditional_tokens)

  conditional_tokens.each do |condition, token|

    do_something_with(token) if condition.call

  end

end

```



When given C-Level procs, it makes sense to call them with `self` to evaluate the corresponding method.



```ruby

some_interface(&:foo? => "foo", &:bar? => "bar" )

```



```ruby

def foo? = true

def bar? = false



def some_interface(**conditional_tokens)

  conditional_tokens.each do |condition, token|

    case condition

    when CProc

      do_something_with(token) if condition.call(self)

    else

      do_something_with(token) if condition.call

    end

  end

end

```







-- 

https://bugs.ruby-lang.org/

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