From: "matz (Yukihiro Matsumoto) via ruby-core" <ruby-core@...>
Date: 2026-09-10T23:38:14+00:00
Subject: [ruby-core:126650] [Ruby Feature#22238] String#tr to take a Hash for multi-character replacements

Issue #22238 has been updated by matz (Yukihiro Matsumoto).

Status changed from Closed to Open
Assignee set to byroot (Jean Boussier)

Reopened. I am satisfied with the spec, but the current implementation (master 3742091) has bugs.

```ruby
"hello".tr("x" => "y")   #=> nil (should be "hello")
"hello".tr({})           #=> nil (should be "hello")

s = +"hello"
s.tr!("x" => "y")        #=> nil
s                        #=> "" (the receiver is emptied)

"0123456789abcdefghij".tr("h" => "H", "2" => "@")
#=> "0123456789abcdefgHij" ("2" is not replaced)
```

* When nothing is replaced, `tr` returns `nil`, and `tr!` empties the receiver. The spec for `tr!` only checks the return value, so it passes.
* On strings of 16 bytes or longer, the SIMD search only finds the first key. The loop that merges the matches of other keys starts with `for (i = i; ...)` and never runs. With more than 16 keys, the SSE2 version finds nothing.

Also:

* The call-seq and document of `tr` do not mention the Hash form.
* A broken string raises `ArgumentError` in non-fastpath encodings, but not in UTF-8/US-ASCII/BINARY. It should be consistent (the 2-argument form raises).

Please add tests for these cases as well.

Matz.

----------------------------------------
Feature #22238: String#tr to take a Hash for multi-character replacements
https://bugs.ruby-lang.org/issues/22238#change-118908

* Author: byroot (Jean Boussier)
* Status: Open
* Assignee: byroot (Jean Boussier)
----------------------------------------
This is @matz's counter proposal to [Feature #22229] from the last dev-meeting

> matz: I will counter-propose String#tr-with-hash style.

```ruby
'Hello </script>'.tr(">" => '\u003e', "<" => '\u003c', "&" => '\u0026') # matz: OK

'Hello </script>'.tr("abc" => 'ABC') # should raise an exception
'Hello </script>'.tr("abc" => 'ABC', "ab" => "XY") # should raise an exception

"f��e".tr("��" => "���") # it should work

"Hello".tr("l" => "ABC", "o" => "XYZ") #=> "HeABCABCXYZ"

"Hello".gsub(/./m) { hash[$&] || $& } # gsub equivalent
```

Notes:

- Hash keys MUST be single characters (but can be multi-byte).
- Values can be multiple characters.



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