[ruby-core:107667] [Ruby master Feature#16295] Chainable aliases for String#-@ and String#+@

["Eregon (Benoit Daloze)" <noreply@ruby-lang.org>]

Issue #16295 has been updated by Eregon (Benoit Daloze).


> .dup is not quite as good, as it always allocates a copy.

It creates a new String instance, which is what one needs to guarantee safe mutation without affecting other parts of the program.
Hence, `+@` should rarely be used (only if we know where all the strings passed to this method come from and it's OK to mutate them).
`.dup` does not copy the actual bytes until mutated, because Strings are copy-on-write.

> how is -@ different from .freeze ? The meaning of these seems very much the same.

`-@` interns and might return a different String instance, `.freeze` does not intern and always returns the receiver.

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Feature #16295: Chainable aliases for String#-@ and String#+@
https://bugs.ruby-lang.org/issues/16295#change-96586

* Author: byroot (Jean Boussier)
* Status: Open
* Priority: Normal
----------------------------------------
Original discussion https://bugs.ruby-lang.org/issues/16150?next_issue_id=16147&prev_issue_id=16153#note-40

In #16150, @headius raised the following concern about `String#-@` and `String#+@`:

headius (Charles Nutter) wrote:
> > Not exactly, -@ and +@ makes this much simpler
> 
> I do like the unary operators, but they also have some precedence oddities:
> 
> ```
> >> -"foo".size
> => -3
> >> (-"foo").size
> => 3
> ```
> 
> And it doesn't work at all if you're chaining method calls:
> 
> ```
> >> +ary.to_s.frozen?
> NoMethodError: undefined method `+@' for false:FalseClass
> 	from (irb):8
> 	from /usr/bin/irb:11:in `<main>'
> ```
> 
> But you are right, instead of the explicit `dup` with possible freeze you could use `-` or `+` on the result of `to_s`. However it's still not safe to modify it since it would modify the original string too.

After working for quite a while with those, I have to say I agree. They very often force to use parentheses, which is annoying, and an indication that regular methods would be preferable to unary operators.


In response @matz proposed to alias them as `String#+` and `String#-` without arguments:

>  How about making String#+ and #- without argument behave like #+@ and #-@ respectively, so that we can write:
>  
>  ```
>  "foo".-.size
>  ary.to_s.+.frozen?
>  ```


My personal opinion is that descriptive method names would be preferable to `+/-`:

> IMHO `.-` and `.+` is not very elegant. Proper method names explaining the intent would be preferable.
> 
>   - `-@` could be `dedup`, or `deduplicate`.
>   - `+@` could be `mutable` or `mut`.





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