Feature #21346: Introduce `String#ensure_suffix`

• Status: Open
• Assignee: -
• Target version: -

[matheusrich (Matheus Richard)]

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 queries that might find this pattern in other places:

1. for Ruby: /end(?:s)?_with\?\(['"].*['"]\) \?/ lang:ruby -is:fork
2. 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, 2)).

I've gone ahead and implemented String#ensure_suffix in a pull request but the suggested behavior is this:

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

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

[matheusrich (Matheus Richard)]

If approved, I can add String#ensure_prefix and the bang versions of those methods.

[duerst (Martin Dürst)]

You say "queries that might find this pattern". That seems to say that you haven't found it yet.

What's the result for

"Hello".ensure_suffix("o!")

Is it "Helloo!", or is it "Hello!"?

[matheusrich (Matheus Richard)]

You say "queries that might find this pattern". That seems to say that you haven't found it yet.

I'm not sure what you mean. I just meant that the regex can find this pattern, but I can't guarantee it will only find that.

What's the result for

"Hello".ensure_suffix("o!")

Is it "Helloo!", or is it "Hello!"?

As currently implemented, it returns "Helloo!"

[nobu (Nobuyoshi Nakada)]

matheusrich (Matheus Richard) wrote in #note-3:

You say "queries that might find this pattern". That seems to say that you haven't found it yet.

I'm not sure what you mean. I just meant that the regex can find this pattern, but I can't guarantee it will only find that.

Maybe like this?

"Hell".sub(/(?<!o!)\z/, "o!")   #=> "Hello!"
"Hello!".sub(/(?<!o!)\z/, "o!") #=> "Hello!"
"o!Hell".sub(/(?<!o!)\z/, "o!") #=> "o!Hello!"

What's the result for

"Hello".ensure_suffix("o!")

Is it "Helloo!", or is it "Hello!"?

As currently implemented, it returns "Helloo!"

You should describe the corner case in the doc, and the test preferably.

[matheusrich (Matheus Richard)]

@nobu (Nobuyoshi Nakada) added! Thanks for the review.