[ruby-core:111588] [Ruby master Feature#19302] Non-destructive String#insert

Issue #19302 has been updated by jeremyevans0 (Jeremy Evans).


austin (Austin Ziegler) wrote in #note-2:
> Ruby strings are mostly copy-on-write, so `string.dup.insert(3, 'baz')` would solve the issue, and it could be written (I believe) as `-string.insert(3, 'baz')` in modern Ruby.

`-string.insert(3, 'baz')` is parsed as `-(string.insert(3, 'baz'))`, which is not the order of operations desired, since it is definitely destructive. Also, you don't want `-`, as that is `dedup` (`(-string).insert(3, 'baz')` results in a FrozenError).  Maybe you were thinking of `+string` instead of `-string`, but if `string` is mutable, that doesn't make a copy, so it becomes a destructive operation. The initial suggestion of `string.dup.insert(3, 'baz')` makes the most sense.

In terms of the feature request, I'm against adding such a method.  The need for it seems uncommon, and it is easy to use `dup` to handle it when it is needed.

----------------------------------------
Feature #19302: Non-destructive String#insert
https://bugs.ruby-lang.org/issues/19302#change-100958

* Author: noraj (Alexandre ZANNI)
* Status: Open
* Priority: Normal
----------------------------------------
It would be nice to have a non-destructive version of String#insert to be able to work with frozen literals.

## Current behavior

There is only a destructive version of `String#insert` that will throw an error if the string is frozen.

```ruby
irb(main):007:0> a = 'foobar'.freeze
irb(main):008:0> b = a.insert(3,'baz')
(irb):8:in `insert': can't modify frozen String: "foobar" (FrozenError)
        from (irb):8:in `<main>'                                  
        from /home/noraj/.asdf/installs/ruby/3.2.0/lib/ruby/gems/3.2.0/gems/irb-1.6.2/exe/irb:11:in `<top (required)>'
        from /home/noraj/.asdf/installs/ruby/3.2.0/bin/irb:25:in `load'
        from /home/noraj/.asdf/installs/ruby/3.2.0/bin/irb:25:in `<main>'
```

This can happen pretty quickly when you have `# frozen_string_literal: true` in all your files.

## Idea of implementation

```ruby
def insert_nd(idx, str2)
  self[0...idx] + str2 + self[idx..]
end
```

Note: this is a draft, as it doesn't handle negative index in the same way as insert

## Idea of naming

Ideally the actual `String#insert` would have been `String#insert!` so that the non-destructive version could be `String#insert`, but naturally that won't do as a renaming will cause a breaking change.

A more viable option would be to name it `insert_nd` (nd for non-destructive) but it's may not be following a naming convention.

Another idea to avoid confusion would be to avoid using `insert` and rather use a synonym like _place_, _slip_, _slot_, _lodge_, etc.



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