From: "byroot (Jean Boussier)" <noreply@ruby-lang.org>
To: ruby-core@ruby-lang.org
Subject: [ruby-core:109403] [Ruby master Feature#18951] Object#with to set and restore attributes around a block
Date: Mon, 01 Aug 2022 17:52:26 +0000 (UTC) [thread overview]
Message-ID: <redmine.issue-18951.20220801175226.7941@ruby-lang.org> (raw)
In-Reply-To: redmine.issue-18951.20220801175226.7941@ruby-lang.org
Issue #18951 has been reported by byroot (Jean Boussier).
----------------------------------------
Feature #18951: Object#with to set and restore attributes around a block
https://bugs.ruby-lang.org/issues/18951
* Author: byroot (Jean Boussier)
* Status: Open
* Priority: Normal
----------------------------------------
### Use case
A very common pattern in Ruby, especially in testing is to save the value of an attribute, set a new value, and then restore the old value in an `ensure` clause.
e.g. in unit tests
```ruby
def test_something_when_enabled
enabled_was, SomeLibrary.enabled = SomeLibrary.enabled, true
# test things
ensure
SomeLibrary.enabled = enabled_was
end
```
Or sometime in actual APIs:
```ruby
def with_something_enabled
enabled_was = @enabled
@enabled = true
yield
ensure
@enabled = enabled_was
end
```
There is no inherent problem with this pattern, but it can be easy to make a mistake, for instance the unit test example:
```ruby
def test_something_when_enabled
some_call_that_may_raise
enabled_was, SomeLibrary.enabled = SomeLibrary.enabled, true
# test things
ensure
SomeLibrary.enabled = enabled_was
end
```
In the above if `some_call_that_may_raise` actually raises, `SomeLibrary.enabled` is set back to `nil` rather than its original value. I've seen this mistake quite frequently.
### Proposal
I think it would be very useful to have a method on Object to implement this pattern in a correct and easy to use way. The naive Ruby implementation would be:
```ruby
class Object
def with(**attributes)
old_values = attributes.dup
attributes.each_key do |key|
old_values[key] = public_send(key)
end
begin
attributes.each do |key, value|
public_send("#{key}=", value)
end
yield
ensure
old_values.each do |key, old_value|
public_send("#{key}=", old_value)
end
end
end
end
```
NB: `public_send` is used because I don't think such method should be usable if the accessors are private.
With usage:
```ruby
def test_something_when_enabled
SomeLibrary.with(enabled: true) do
# test things
end
end
```
```ruby
GC.with(measure_total_time: true, auto_compact: false) do
# do something
end
```
### Alternate names and signatures
If `#with` isn't good, I can also think of:
- `Object#set`
- `Object#apply`
But the `with_` prefix is by far the most used one when implementing methods that follow this pattern.
Also if accepting a Hash is dimmed too much, alternative signatures could be:
- `Object#set(attr_name, value)`
- `Object#set(attr1, value1, [attr2, value2], ...)`
--
https://bugs.ruby-lang.org/
next parent reply other threads:[~2022-08-01 17:52 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-01 17:52 byroot (Jean Boussier) [this message]
2022-08-27 14:37 ` [ruby-core:109737] [Ruby master Feature#18951] Object#with to set and restore attributes around a block nobu (Nobuyoshi Nakada)
2022-08-27 14:58 ` [ruby-core:109738] " Eregon (Benoit Daloze)
2022-08-27 15:06 ` [ruby-core:109739] " byroot (Jean Boussier)
2022-08-27 15:14 ` [ruby-core:109740] " retro
2022-08-27 15:22 ` [ruby-core:109741] " byroot (Jean Boussier)
2022-08-29 12:08 ` [ruby-core:109766] " ufuk (Ufuk Kayserilioglu)
2022-08-29 12:31 ` [ruby-core:109767] " byroot (Jean Boussier)
2022-08-29 14:11 ` [ruby-core:109771] " ngan (Ngan Pham)
2022-08-31 20:05 ` [ruby-core:109801] " Dan0042 (Daniel DeLorme)
2022-08-31 21:12 ` [ruby-core:109803] " austin (Austin Ziegler)
2022-09-01 10:37 ` [ruby-core:109809] " p8 (Petrik de Heus)
2022-09-11 2:34 ` [ruby-core:109881] " retro
2022-09-11 2:49 ` [ruby-core:109882] " baweaver (Brandon Weaver)
2022-09-21 5:58 ` [ruby-core:109969] " ko1 (Koichi Sasada)
2022-09-21 6:03 ` [ruby-core:109970] " byroot (Jean Boussier)
2022-09-23 15:40 ` [ruby-core:110049] " Dan0042 (Daniel DeLorme)
2022-11-15 9:18 ` [ruby-core:110760] " byroot (Jean Boussier)
2022-12-01 7:36 ` [ruby-core:111111] " matz (Yukihiro Matsumoto)
2022-12-01 7:38 ` [ruby-core:111112] " byroot (Jean Boussier)
2022-12-10 17:10 ` [ruby-core:111252] " retro
2023-03-06 8:18 ` [ruby-core:112698] " byroot (Jean Boussier) via ruby-core
2023-03-17 1:15 ` [ruby-core:112920] " dsisnero (Dominic Sisneros) via ruby-core
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