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Super readable String operations with `delete_prefix` and `delete_suffix`

swanson profile image matt swanson Originally published at boringrails.com on ・2 min read

One reason I love writing Ruby is that it’s optimized for programmer happiness. The Ruby community values code that is super readable.

Programmers coming from other ecosystems are often shocked at much Ruby looks like pseudo-code. Between the standard library and extensions like ActiveSupport, working with Ruby means you can write code in a natural way.

A great example of this are the String methods delete_prefix and delete_suffix.

Usage

You can use delete_prefix to, as the name says, delete a substring from the beginning of a string.

"BoringRails!".delete_prefix("Boring")
#=> "Rails!"

"#programming".delete_prefix("#")
#=> "programming"

"ISBN: 9780091929787".delete_prefix("ISBN: ")
#=> "9780091929787"

"mailto:test@example.com".delete_prefix("mailto:")
#=> "test@example.com"

github_url = "https://github.com/rails/rails"
repo_name = github_url.delete_prefix("https://github.com/")
#=> "rails/rails"
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Compare this method to other options like gsub:

github_url = "https://github.com/rails/rails"
repo_name = github_url.gsub("https://github.com/", "")
#=> "rails/rails"
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While gsub is more flexible (it can take a Regex and swap multiple occurences), the code doesn’t read as naturally as delete_prefix. And delete_prefix is more performant!

If you want to remove characters at the end of a string, you have two main options: chomp and delete_suffix.

"report.csv".chomp(".csv")
#=> "report"

"report.csv".delete_suffix(".csv")
#=> "report"

"150 cm".delete_suffix("cm").to_i
#=> 150
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Stylistically, chomp has a bit more of the whimsy that you might expect from Ruby, while delete_suffix is a nice mirroring of delete_prefix and more explicitly named. Both have similar performance benchmarks and are faster than sub.

Additional Resources

Ruby API Docs: String#delete_prefix

Ruby API Docs: String#delete_suffix

Ruby Bug Tracker: Feature discussion

String method benchmarks: Fast Ruby - String


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