From: "ufuk (Ufuk Kayserilioglu) via ruby-core" <ruby-core@...>
Date: 2025-06-05T16:57:04+00:00
Subject: [ruby-core:122462] [Ruby Feature#21346] Introduce `String#ensure_suffix`

Issue #21346 has been updated by ufuk (Ufuk Kayserilioglu).


I personally find the `"Hello".ensure_suffix("o!")` case returning `"Helloo!"` very unexpected. I would have expected the change in the string to be the minimal operation needed to ensure that the string ends with the given suffix (i.e. for the result of the example to be `"Hello!"`), but this isn't what's happening.

@matz Is this the behaviour that you want?

----------------------------------------
Feature #21346: Introduce `String#ensure_suffix`
https://bugs.ruby-lang.org/issues/21346#change-113650

* Author: matheusrich (Matheus Richard)
* Status: Open
----------------------------------------

## Problem

Ensuring a string has a specific suffix or prefix is a common operation in many applications.
Bundler itself uses it:

https://github.com/rubygems/rubygems/blob/d409ec8b5fc647fabe30e37e17cd1ea857634f6b/bundler/lib/bundler/uri_normalizer.rb#L17

Here are [GitHub search](https://github.com/search) queries that might find this pattern in other places:
1. for Ruby: `/end(?:s)?_with\?\(['"].*['"]\) \?/ lang:ruby -is:fork`
1. for Crystal (a language very similar to Ruby): `/ends_with\?\(['"].*['"]\) \?/ lang:crystal -is:fork`

## Suggested solution

I believe Ruby would benefit from having a first-class method for this purpose.
I suggest the `String#ensure_suffix` and `String#ensure_prefix` methods.

I think these names are intuitive enough (here are 2 examples of people using `ensure` for this purpose ([1](https://github.com/boltops-tools/ufo/blob/796104fdb89163d09a58fad42add697923c18294/lib/ufo/cfn/stack/builder/resources/dns.rb#L76), [2](https://github.com/mumuki/mumuki-domain/blob/6194089d82b1a0c8805ecba98e006deb1694dc8e/lib/mumuki/domain/extensions/string.rb#L6))).

I've gone ahead and implemented `String#ensure_suffix` in a [pull request](https://github.com/ruby/ruby/pull/13366) but the suggested behavior is this:

```rb
"Hell".ensure_suffix("o!")   # => "Hello!"
"Hello!".ensure_suffix("o!") # => "Hello!"

s = "Hello!"
s.ensure_suffix("!").equal?(s) # => true # returns same object if already suffixed
```





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