Issue #11782 has been updated by Koichi Sasada.


Quoted from DevelopersMeeting20151021Japan log:
https://bugs.ruby-lang.org/projects/ruby/wiki/DevelopersMeeting20151021Japanhttps://docs.google.com/document/d/1axnQv1A2SdRExw--_RzXXJAPrRyvN7MCIB0WrKcZaSE/pub

> matz: i have another idea +°»...°… -> mutable, -°…...°… -> immutable. it is more clean than °»...°….freeze. how about that, instead of the magic comment? i don°«t care about pull-requests, but care about the representation of source code.
> akr: °ń
> matz: I don°«t like magic comment, so that I hesitate to introduceit.
> a_matsuda: + and - seems string operation.  << -°…foo°… canbe seen as a here document.
> matz: I understand.  + and - is not good idea.
> matz: another idea: make °∆°«°«foo°«°«°« frozen.  incompatibility is negligible.
> matz: yet another idea: make single quoted strings frozen. This is incompatible.

Matz said "+ and - is not good idea.".
So that please check it.


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Feature #11782: String#+@ and String#-@
https://bugs.ruby-lang.org/issues/11782#change-55329

* Author: Koichi Sasada
* Status: Assigned
* Priority: Normal
* Assignee: Yukihiro Matsumoto
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Matz said 

> In fact, my best choice is introducing `String#+` that returns a mutable copy of a string.
[ruby-core:71879] [Ruby trunk - Bug #11759] 

So that this is a ticket for that.
I'll commit it ASAP to check this methods before 2.3.

Specification:

* `+'foo'` returns modifiable string.
* `-'foo'` returns frozen string (because wasters will freeze below 0 degree in Celsius).




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