CODEWITHSUNDEEP
ruby-on-railsruby
Sumit Sharma
Sumit Sharma

Reputation: 93

Convert string into class name without throwing error

I am trying to convert the string into classname using constantize. But it throws error if the classname is not present or the string is empty or nil.

Is there any way to convert the string into classname without throwing error. Or returning false only if not able to convert.

Upvotes: 1

Views: 1214

Answers (5)

radoAngelov
radoAngelov

Reputation: 714

Firstly, I want to point out something from the answers above. rescue false means that all kinds of exceptions thrown from that expression are rescued as false. This means that even if you have an exception object of class NoMethodError or RuntimeError you will return false and your expectation would be that the constantized string does not match a constant in your app. This can cause you hours of debugging if you don't know how the error handling system in ruby is working. It is also a place to introduce a lot of bugs in your code in the future.

I see the ruby-on-rails tag so I assume you are running a problem in a rails app. You can use a helper method coming from the ActiveSupport::Inflector module. Instead of rescuing the constantize method you would probably want to use the safe_constantize. It will return nil in case the constant is not present in your project.

Example usage (note I haven't defined a Foo constant in my project):

# with constantize
irb(main) > 'foo'.constantize
=> NameError (wrong constant name foo)

# with safe_contantize 
irb(main) > 'foo'.safe_constantize
=> nil

Upvotes: 4

mrzasa
mrzasa

Reputation: 23327

You can provide a default value or return early in case of nil and then rescue a NameError:

def to_class(name)
   # default to empty string
   (name || "").constantize
rescue NameError
   false 
end 

def to_class(name)
   # guard against invalid input
   return false if name.nil?

   name.constantize
rescue NameError
   false 
end

EDIT: It's longer than simple 

string.constantize rescue false

but IMO you should rescue the most specific error you can. rescue false is OK for simple scripts or some test cases. In production code it's quite risky - you could hide some exceptions that should be verbose.

Upvotes: 0

Aleksei Matiushkin
Aleksei Matiushkin

Reputation: 121000

I hate Rails, it brings a ton of redundant so-called helpers, having zero value in general. This might be easily done with pure Ruby:

Kernel.const_get(string) if Kernel.const_defined?(string)

The above effectively returns the class or nil (which is falsey in Ruby) if the class is not defined.

Upvotes: 5

ray
ray

Reputation: 5552

You can achieve it by following,

string.constantize rescue false

Additional

If you have have downcase string or table name for that, it can also be converted into class name by using classify method as follows,

string.classify.constantize rescue false

If you have string 'event_managers', it will return class EventManager

Upvotes: 0

arieljuod
arieljuod

Reputation: 15838

What's the error? if it's an exception you can do something like:

the_class = your_string.constantize rescue false

The rescue catches de exception and returns false in that case.

Upvotes: 0

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