[ruby-core:108417] [Ruby master Feature#18757] Introduce %R for anchored regular expression patterns
From:
"zeke (Zeke Gabrielse)" <noreply@...>
Date:
2022-04-27 15:00:05 UTC
List:
ruby-core #108417
Issue #18757 has been updated by zeke (Zeke Gabrielse).
Description updated
Fix `validates_format` pattern
----------------------------------------
Feature #18757: Introduce %R for anchored regular expression patterns
https://bugs.ruby-lang.org/issues/18757#change-97449
* Author: zeke (Zeke Gabrielse)
* Status: Open
* Priority: Normal
----------------------------------------
When defining regular expression patterns, it's often the case that you want to anchor with `\A` and `\z` to match the full text input, rather than `^` and `$`, respectively, which may (unintentionally) match text including newlines. This is especially true in the context of an web application such as a Rails app. Unfortunately, `\A` and `\z` reduce the legibility of a regular expression.
For example, take this `ActionMailbox` usage:
```ruby
class ApplicationMailbox < ActionMailbox::Base
routing %r{\Areplies\+.*?@ruby-lang\.org\z}i => :replies
routing %r{\Asales@.*?\z}i => :leads
end
```
At first glance, it may look as if the second route matches `Asales`, but that's not the case upon further inspection. To improve legibility, a developer may choose to use `^` instead of `\A`. Because when defining a pattern using `\A` and `\z`, readability suffers, but especially for `\A`. In other cases, developers forget to use `\A` and `\z` over `^` or `$` when validating or matching against user input.
I propose Ruby introduces a new percent-notation, `%R{}`, for defining interpolated regular expression patterns that automatically anchor a pattern with `\A` and `\z`.
For example, the above will look like below:
```ruby
class ApplicationMailbox < ActionMailbox::Base
routing %R{replies\+.*?@ruby-lang\.org}i => :replies
routing %R{sales@.*?}i => :leads
end
```
This is much more readable, and it's safer — developers using `%R{}` are not going to accidentally use `^` or `$` instead of `\A` and `\z`, respectively (the former being vulnerable to matching input data containing newlines).
This is especially useful in pattern matching data where some values may be a symbol or a string, depending on where the data originated (internally vs externally):
```ruby
data = { type: :foo, id: 1 } # Could also be: { type: 'foo', id: 1 }
case data
in type: %R(foo), id:
# ...
else
end
```
Formally, the new anchored regex percent notation would work as follows:
```ruby
re = %R(test)
# => /\Atest\z/
re.match?('test') # => true
re.match?('testing') # => false
re.match?('a test') # => false
re.match?(:test) # => true
re.match?(:testing) # => false
re.match?(:a_test) # => false
```
This would also be useful for data validation purposes, where a developer could clean up patterns that previously used regular expressions with `\A...\z` and `^...$`, such as with Rails model validations, e.g. `validates_format(with: %R{[-a-z0-9]+)`
I do understand that having an uppercase `%R` behaves differently than other percent notations (i.e. lowercase is typically non-interpolated, uppercase interpolated), but since `%r` already allows interpolation, I figured it was okay to be a bit different. Regardless — I'm open to other syntax suggestions.
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