From: merch-redmine@jeremyevans.net
To: ruby-core@ruby-lang.org
Subject: [ruby-core:95139] [Ruby master Feature#16166] Remove exceptional treatment of *foo when it is the sole block parameter
Date: Fri, 27 Sep 2019 23:03:58 +0000 (UTC) [thread overview]
Message-ID: <redmine.journal-81778.20190927230357.de8bf67089ff18a3@ruby-lang.org> (raw)
In-Reply-To: redmine.issue-16166.20190913081711@ruby-lang.org
Issue #16166 has been updated by jeremyevans0 (Jeremy Evans).
matz (Yukihiro Matsumoto) wrote:
> I think the following code behavior is wrong:
> ```ruby
> p instance_exec(["a"]){|*foo, **bar| foo } #=> ["a"]
> ```
> It should return `[["a"]]`.
Here's a pull request for that: https://github.com/ruby/ruby/pull/2502
Note that it breaks some tests/specs. I believe the reason methods with keywords were handled differently is because the last element of the argument could be used as keywords:
```
$ ruby -e "p proc{|*foo, **bar| [foo, bar]}.call([1, {a: 1}])"
-e:1: warning: The last argument is used as the keyword parameter
-e:1: warning: for `call' defined here
[[1], {:a=>1}]
```
As you can see, this now raises a warning in Ruby 2.7, and behavior will change in Ruby 3.0. Do we want to make this change in 2.7, or do we want to wait for 3.0?
----------------------------------------
Feature #16166: Remove exceptional treatment of *foo when it is the sole block parameter
https://bugs.ruby-lang.org/issues/16166#change-81778
* Author: sawa (Tsuyoshi Sawada)
* Status: Open
* Priority: Normal
* Assignee:
* Target version:
----------------------------------------
In the parameter signature of a code block for a method that is not involved in method definition or creation of lambda objects, two types of arguments `["a"]` and `"a"` are neutralized:
```ruby
instance_exec(["a"]){|foo, bar| foo} # => "a"
instance_exec("a"){|foo, bar| foo} # => "a"
instance_exec(["a"]){|*foo, **bar| foo} # => ["a"]
instance_exec("a"){|*foo, **bar| foo} # => ["a"]
```
This is the same behavior as with assignment constructions:
```ruby
foo, bar = ["a"]; foo # => "a"
foo, bar = "a"; foo # => "a"
*foo = ["a"]; foo # => ["a"]
*foo = "a"; foo # => ["a"]
```
And it contrasts with constructions involved in method definition or creation of lambda objects, where the distinction is preserved:
```ruby
lambda{|foo| foo}.call(["a"]) # => ["a"]
lambda{|foo| foo}.call("a") # => "a"
->(foo){foo}.call(["a"]) # => ["a"]
->(foo){foo}.call("a") # => "a"
lambda{|*foo| foo}.call(["a"]) # => [["a"]]
lambda{|*foo| foo}.call("a") # => ["a"]
->(*foo){foo}.call(["a"]) # => [["a"]]
->(*foo){foo}.call("a") # => ["a"]
```
However, when `*foo` is the sole parameter of a code block for a method that is not involved in method definition or creation of lambda objects, `["a"]` and `"a"` are not neutralized:
```ruby
instance_exec(["a"]){|*foo| foo} # => [["a"]]
instance_exec("a"){|*foo| foo} # => ["a"]
```
behaving in contrast to assignment constructions, and rather on a par with constructions involved in method definition or creation of lambda objects.
Particularly, existence or absence of another parameter `**bar` entirely changes what `foo` refers to:
```ruby
instance_exec(["a"]){|*foo| foo} # => [["a"]]
instance_exec(["a"]){|*foo, **bar| foo} # => ["a"]
```
I find this behavior inconsistent and confusing. I would like to request to remove this exceptional treatment of splatted parameter `*foo` when it is the sole parameter in a code block. I request this behavior:
```ruby
instance_exec(["a"]){|*foo| foo} # => ["a"]
```
--
https://bugs.ruby-lang.org/
next prev parent reply other threads:[~2019-09-27 23:04 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <redmine.issue-16166.20190913081711@ruby-lang.org>
2019-09-13 8:17 ` [ruby-core:94925] [Ruby master Feature#16166] Remove exceptional handling of *foo when it is the sole block parameter sawadatsuyoshi
2019-09-13 10:16 ` [ruby-core:94926] [Ruby master Feature#16166] Remove exceptional treatment " mame
2019-09-13 15:44 ` [ruby-core:94929] " shevegen
2019-09-13 15:45 ` [ruby-core:94930] " shevegen
2019-09-25 3:00 ` [ruby-core:95073] " matz
2019-09-27 23:03 ` merch-redmine [this message]
2019-10-22 18:00 ` [ruby-core:95472] " daniel
2019-11-27 17:55 ` [ruby-core:95996] " eregontp
2019-12-02 15:55 ` [ruby-core:96059] " daniel
2020-01-05 16:06 ` [ruby-core:96671] " sawadatsuyoshi
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