From: shugo@ruby-lang.org
To: ruby-core@ruby-lang.org
Subject: [ruby-core:76316] [Ruby trunk Feature#12086] using: option for instance_eval etc.
Date: Fri, 08 Jul 2016 07:56:20 +0000 [thread overview]
Message-ID: <redmine.journal-59552.20160708075620.bc3fd5fbb67fad99@ruby-lang.org> (raw)
In-Reply-To: redmine.issue-12086.20160219073402@ruby-lang.org
Issue #12086 has been updated by Shugo Maeda.
Nobuyoshi Nakada wrote:
> I'm against `instance_eval` under the hood by libraries.
I used to be against it too, but it's common now whether `using:` is available or not.
Let me talk about a use case.
I wrote a packrat parser library called radd_djur (https://github.com/shugo/radd_djur) before.
radd_djur uses refinements to implement an internal DSL to define grammar rules.
```ruby
require "radd_djur"
using RaddDjur::DSL
calc = RaddDjur::Grammar.new(:expr) {
define :expr do
[:int, "+", :int].bind { |x, *, y|
ret x + y
} /
[:int, "-", :int].bind { |x, *, y|
ret x - y
}
end
define :int do
(?0..?9).one_or_more.bind { |xs|
ret xs.foldl1(&:+).to_i
}
end
}
p calc.parse("123+456")
```
`define` and `ret` are provided by `instance_eval`, and `bind`, `/`, and `one_or_more`
are provided by refinements.
It looks cool, but there are two problems here:
1. We have to write `using RaddDjur::DSL` explicitly.
2. Refinements for DSL is available out of the grammar rules.
If `instance_eval(using: refinement)` is introduced, RaddDjur::DSL can be activated
only in the block given to `RaddDjur::Grammar.new`, and these two problems will be solved.
Note that `instance_eval` and refinement activation have to be done atomically in this case.
That's why I proposed this feature as a new option of `instance_eval`.
----------------------------------------
Feature #12086: using: option for instance_eval etc.
https://bugs.ruby-lang.org/issues/12086#change-59552
* Author: Shugo Maeda
* Status: Open
* Priority: Normal
* Assignee:
----------------------------------------
Currently refinements can be activated only in toplevel or class/module definitions.
If they can be activated in block-level, it's useful to implement internal DSLs.
How about to add a new option using: for Kernel#instance_eval and Moule#{class,module}_eval?
```ruby
module FixnumDivExt
refine Fixnum do
def /(other)
quo(other)
end
end
end
p 1 / 2 #=> 0
instance_eval(using: FixnumDivExt) do
p 1 / 2 #=> (1/2)
end
p 1 / 2 #=> 0
```
Proof-of-concept implementation is available at <https://github.com/shugo/ruby/tree/eval_using>.
In my previous proposal before Ruby 2.0, refinements used in a class or module are
implicitly activated by instance_eval and class_eval, but now I think it's better to
explicitly specify refinements to be activated.
Considerations:
* In the PoC implementation, refined methods are not cached inline, and thus it decreases
the performance of refined method call.
If there is a way to guarantee that blocks never be evaluated in different environments,
refined methods can be cached inline.
* {instance,class,module}_exec cannot be extended in the same way, because they take arbitrary
arguments and there's no way to distinguish an option hash from the last argument hash.
--
https://bugs.ruby-lang.org/
next prev parent reply other threads:[~2016-07-08 7:22 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <redmine.issue-12086.20160219073402@ruby-lang.org>
2016-02-19 7:34 ` [ruby-core:73886] [Ruby trunk Bug#12086] using: option for instance_eval etc shugo
2016-02-19 10:01 ` [ruby-core:73887] [Ruby trunk Feature#12086] " shugo
2016-06-13 7:27 ` [ruby-core:75972] " nobu
2016-06-13 7:31 ` [ruby-core:75975] " matz
2016-07-08 7:56 ` shugo [this message]
2016-07-08 8:02 ` [ruby-core:76317] " shugo
2016-07-08 12:58 ` [ruby-core:76320] " nobu
2016-07-09 0:17 ` [ruby-core:76326] " shugo
2016-07-20 2:42 ` [ruby-core:76463] " shyouhei
2016-09-07 8:10 ` [ruby-core:77196] " tom.enebo
2016-09-07 12:43 ` [ruby-core:77208] " headius
2016-09-07 13:59 ` [ruby-core:77209] " headius
2016-09-07 14:08 ` [ruby-core:77211] " headius
2016-09-07 14:22 ` [ruby-core:77212] " headius
2016-09-08 23:27 ` [ruby-core:77223] " shugo
2016-09-08 23:36 ` [ruby-core:77224] " shugo
2016-09-08 23:40 ` [ruby-core:77225] " shugo
2016-09-09 1:20 ` [ruby-core:77226] " headius
2016-09-09 3:08 ` [ruby-core:77227] " shugo
2019-12-29 19:46 ` [ruby-core:96583] [Ruby master " eregontp
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-list from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
List information: https://www.ruby-lang.org/en/community/mailing-lists/
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=redmine.journal-59552.20160708075620.bc3fd5fbb67fad99@ruby-lang.org \
--to=ruby-core@ruby-lang.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).