From: "Eregon (Benoit Daloze)" <noreply@...>
Date: 2022-02-22T18:44:31+00:00
Subject: [ruby-core:107716] [Ruby master Feature#18597] Strings need a named method like `dup` that doesn't duplicate if receiver is mutable

Issue #18597 has been updated by Eregon (Benoit Daloze).


I meant code in a gem or in some open-source repository, so we can see the context and the need.

That example seems a clear case for String interpolation:
```ruby
"#{some_object.send(a_method)}blah"
```

> and I don't want to raise exception if I don't absolutely have to

That is I believe an anti-pattern.
Concretely, a method should either take a String and will never mutate it, or it needs a mutable String/a buffer (and will or can mutate it).
What I'm saying is "might or might not mutate the argument (depending on frozen state)" is a bad design.
A method should be clear about what it expects, it's very hard to work with a method which might mutate or not what you give it.

----------------------------------------
Feature #18597: Strings need a named method like `dup` that doesn't duplicate if receiver is mutable
https://bugs.ruby-lang.org/issues/18597#change-96639

* Author: danh337 (Dan H)
* Status: Open
* Priority: Normal
----------------------------------------
This is related to #16295, but focuses only on the `.+@` part.

Currently we can use `.dup` in a method chain when we need to mutate a String.

However there are cases where the code's context *expects* the String to be mutated. In cases like this, `.dup` always works, but we don't want to duplicate a String that is already mutable.

Since `.+@` looks more like an operator, it can be unintuitive in a method chain, so this is asking for a new named method that can be used in its place, instead of always `.dup`.

For example:
```
def add_result_text(buffer, new_result)
  text = "#{new_result.count} #{new_result.input} #{do_fancy_calc(new_result)}\n"
  buffer.dup_if_immutable << text
  #      ^^^^^^^^^^^^^^^^ new method?
end

buffer = "" # ...maybe immutable

get_lots_of_results.each do |result|
  buffer = add_result_text(buffer, result) # In case it was dup'ed
end
```




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