Safe trying of Enum types

Support dry-types
1

Is there a safe way to test if a value is included in an enum, i.e., without raising an exception if it does not meet constraints? And more generally, when can you not safe try? I was surprised to find that this raises a Dry::Types::ConstraintError since I would have expected a Dry::Types::Result::Failure. Thanks in advance for your help.

carbon (6)
carbon (6)1600×782 83.1 KB

2

Yes, every Dry::Type object responds to #valid? which is a predicate that only returns booleans.

ImageContentType.valid?('image/gif') # => true
ImageContentType.valid?('text/plain') # => false

They also respond to #=== so you can use it with case

case 'application/pdf'
when Types::ImageContentType
  # do something
else
  # do something else
end

I don’t observe it raising on #try, I am getting a Result object:

pry(main)> Types::ImageContentType.try('text/plain')
=> #<Dry::Types::Result::Failure input="text/plain" error=#<Dry::Types::ConstraintError: "text/plain" violates constraints (included_in?(["image/png", "image/jpeg", "image/gif", "image/webp"], "text/plain") failed)>>

If you could give me more information about how you are getting that exception from #try, I can look into it more closely.

1 Like
3

Thank you for the reply @alassek! The most important thing for now is that #valid?/#=== is exactly what I was after.