[ruby-core:93403] [Ruby trunk Feature#15940] Coerce symbols internal fstrings in UTF8 rather than ASCII to better share memory with string literals
From:
eregontp@...
Date:
2019-06-28 09:29:30 UTC
List:
ruby-core #93403
Issue #15940 has been updated by Eregon (Benoit Daloze).
byroot (Jean Boussier) wrote:
> However, there are several ruby specs asserting this behavior, but I don't know if they can be changed or not.
Specs can always be changed, along with `ruby_version_is` guards to specify which behavior on which version (https://github.com/ruby/ruby/blob/trunk/spec/README.md).
Needing to change them indicate a potential incompatibility though.
----------------------------------------
Feature #15940: Coerce symbols internal fstrings in UTF8 rather than ASCII to better share memory with string literals
https://bugs.ruby-lang.org/issues/15940#change-78945
* Author: byroot (Jean Boussier)
* Status: Open
* Priority: Normal
* Assignee:
* Target version:
----------------------------------------
Patch: https://github.com/ruby/ruby/pull/2242
It's not uncommon for symbols to have literal string counterparts, e.g.
```ruby
class User
attr_accessor :name
def as_json
{ 'name' => name }
end
end
```
Since the default source encoding is UTF-8, and that symbols coerce their internal fstring to ASCII when possible, the above snippet will actually keep two instances of `"name"` in the fstring registry. One in ASCII, the other in UTF-8.
Considering that UTF-8 is a strict superset of ASCII, storing the symbols fstrings as UTF-8 instead makes no significant difference, but allows in most cases to reuse the equivalent string literals.
The only notable behavioral change is `Symbol#to_s`.
Previously `:name.to_s.encoding` would be `#<Encoding:US-ASCII>`.
After this patch it's `#<Encoding:UTF-8>`. I can't foresee any significant compatibility impact of this change on existing code.
However, there are several ruby specs asserting this behavior, but I don't know if they can be changed or not: https://github.com/ruby/spec/commit/a73a1c11f13590dccb975ba4348a04423c009453
If this specification is impossible to change, then we could consider changing the encoding of the String returned by `Symbol#to_s`, e.g in ruby pseudo code:
```ruby
def to_s
str = fstr.dup
str.force_encoding(Encoding::ASCII) if str.ascii_only?
str
end
```
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