From: "Eregon (Benoit Daloze)" <noreply@...>
Date: 2021-11-16T12:31:55+00:00
Subject: [ruby-core:106087] [Ruby master Feature#18276] `Proc#bind_call(obj)` same as `obj.instance_exec(..., &proc_obj)`

Issue #18276 has been updated by Eregon (Benoit Daloze).


ko1 (Koichi Sasada) wrote in #note-13:
> `Proc#bind(obj)` returns new Proc or modify the Proc (mutate the Proc)?

Returns a new Proc, mutation would be very bad (similar to changing from proc to lambda semantics).

> My assumption is not same as instance_exec/eval, only replacing the self.

I think we should optimize #instance_exec in CRuby so it only creates the singleton class lazily, like on TruffleRuby.
It seems several people care about that.

Not changing the default definee seems confusing, I think .bind.call/.bind_call should behave like instance_exec in that regard (instance_exec can already be surprising, let's not make an extra variant of it with subtle changes).

----------------------------------------
Feature #18276: `Proc#bind_call(obj)` same as `obj.instance_exec(..., &proc_obj)`
https://bugs.ruby-lang.org/issues/18276#change-94678

* Author: ko1 (Koichi Sasada)
* Status: Open
* Priority: Normal
----------------------------------------
`Proc#bind_call(obj)` same as `obj.instance_exec(..., &proc_obj)`

```ruby
proc_obj = proc{|params...| ...}
obj.instance_exec(params..., &proc_obj)
```

is frequent pattern.

```
$ gem-codesearch 'instance_exec.+\&' | wc -l
9558
```

How about to introduce new method `Proc#bind_call`?

```ruby
class Proc
  def bind_call obj, *args
    obj.instance_exec(*args, &self)
  end
end

pr = ->{ p self }
pr.bind_call("hello") #=> "hello"
pr.bind_call(nil)     #=> nil
```

It is similar to `UnboundMethod#bind_call`.

----

My motivation;

I want to solve shareable Proc's issue https://bugs.ruby-lang.org/issues/18243 and one idea is to prohibit `Proc#call` for shareable Proc's, but allow `obj.instance_exec(&pr)`. To make shortcut, I want to introduce `Proc#bind_call`.

`UnboundProc` is another idea, but I'm not sure it is good idea...

Anyway, we found that there are many usage of `instance_exec(&proc_obj)`, so `Proc#bind_call` is useful not for Ractors.



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