[ruby-core:99512] [Ruby master Feature#16461] Proc#using
From:
shugo@...
Date:
2020-08-08 01:30:00 UTC
List:
ruby-core #99512
Issue #16461 has been updated by shugo (Shugo Maeda).
Assignee set to matz (Yukihiro Matsumoto)
Status changed from Open to Assigned
shugo (Shugo Maeda) wrote in #note-5:
> > I think that could be a good rule, all `Proc#using` must happen `before Proc#call` for a given block.
> > That would mean the code inside a block always calls the same methods (i.e., the refinements for a given call site are fixed), which seems essential to me for sanity when reading code.
>
> OK, I'll try to fix PoC implementation.
Sorry for the delay.
I've fixed the CRuby implementation:
https://github.com/shugo/ruby/pull/2
----------------------------------------
Feature #16461: Proc#using
https://bugs.ruby-lang.org/issues/16461#change-86970
* Author: shugo (Shugo Maeda)
* Status: Assigned
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
* Target version: 2.8
----------------------------------------
## Overview
I propose Proc#using to support block-level refinements.
```ruby
module IntegerDivExt
refine Integer do
def /(other)
quo(other)
end
end
end
def instance_eval_with_integer_div_ext(obj, &block)
block.using(IntegerDivExt) # using IntegerDivExt in the block represented by the Proc object
obj.instance_eval(&block)
end
# necessary where blocks are defined (not where Proc#using is called)
using Proc::Refinements
p 1 / 2 #=> 0
instance_eval_with_integer_div_ext(1) do
p self / 2 #=> (1/2)
end
p 1 / 2 #=> 0
```
## PoC implementation
For CRuby: https://github.com/shugo/ruby/pull/2
For JRuby: https://github.com/shugo/jruby/pull/1
## Background
I proposed [Feature #12086: using: option for instance_eval etc.](https://bugs.ruby-lang.org/issues/12086) before, but it has problems:
* Thread safety: The same block can be invoked with different refinements in multiple threads, so it's hard to implement method caching.
* _exec family support: {instance,class,module}_exec cannot be supported.
* Implicit use of refinements: every blocks can be used with refinements, so there was implementation difficulty in JRuby and it has usability issue in headius's opinion.
## Solutions in this proposal
### Thread safety
Proc#using affects the block represented by the Proc object, neither the specific Proc object nor the specific block invocation.
Method calls in a block are resolved with refinements which are used by Proc#using in the block at the time.
Once all possible refinements are used in the block, there is no need to invalidate method cache anymore.
See [these tests](https://github.com/shugo/ruby/pull/2/commits/1c922614ad7d1fb43b73e195348c81da7a4546ef) to understand how it works.
Which refinements are used is depending on the order of Proc#using invocations until all Proc#using calls are finished, but eventually method calls in a block are resolved with the same refinements.
### * _exec family support
[Feature #12086](https://bugs.ruby-lang.org/issues/12086) was an extension of _eval family, so it cannot be used with _exec family, but Proc#using is independent from _eval family, and can be used with _exec family:
```ruby
def instance_exec_with_integer_div_ext(obj, *args, &block)
block.using(IntegerDivExt)
obj.instance_exec(*args, &block)
end
using Proc::Refinements
p 1 / 2 #=> 0
instance_exec_with_integer_div_ext(1, 2) do |other|
p self / other #=> (1/2)
end
p 1 / 2 #=> 0
```
### Implicit use of refinements
Proc#using can be used only if `using Proc::Refinements` is called in the scope of the block represented by the Proc object.
Otherwise, a RuntimeError is raised.
There are two reasons:
* JRuby creates a special CallSite for refinements at compile-time only when `using` is called at the scope.
* When reading programs, it may help understanding behavior. IMHO, it may be unnecessary if libraries which uses Proc#using are well documented.
`Proc::Refinements` is a dummy module, and has no actual refinements.
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