CODEWITHSUNDEEP
ruby
user5603796
user5603796

Reputation: 389

Custom .is_a? in Ruby

Is it possible to create a custom is_a? in Ruby?

I have a string that can be either a UID or a nickname that I need to check and decide.

UID: 001ABC123 (starts with 3 numeric and ends in 6 alphanumeric characters)

Nickname: john (can be anything but never starts with a number)

I want to be able to do:

t = '001ABC123'

if t.is_a? UID
  ...
end

Is it possible?

Upvotes: 0

Views: 275

Answers (3)

Wand Maker
Wand Maker

Reputation: 18762

If you are looking for succinct way of doing the check, why not use regular expression and match using =~ operator.

This is as neat as using custom is_a? and does not require messing up with String class.

For example:

UID = /^[[:digit:]]{3}[[:alnum:]]{6}$/

t = '001ABC123'

if t =~ UID
   #...
end

Upvotes: 7

Vasfed
Vasfed

Reputation: 18474

Not to pollute global String - use refinements:

class UID < String
end

module CustomStringIsA
  refine String do
    def is_a? what
      if what == UID
        self == '123'
      else
        super
      end
    end
  end
end

puts '123'.is_a?(UID) # false

using CustomStringIsA
puts '123'.is_a?(Fixnum) # false
puts '123'.is_a?(UID) # true

But better use ===, so you can then use case like this:

class UID < String
  def self.=== str
    str === '123'
  end
end

class UID2 < String
  def self.=== str
    str === '456'
  end
end

case '456'
when UID
  puts 'uid'
when UID2
  puts 'uid2'
else
  puts 'else'
end

Upvotes: 0

Daniel Schmidt
Daniel Schmidt

Reputation: 11921

One of the great things about ruby is that you may reopen any class. So an implementation of this may look like this:

class String
    def is_a?(type)
        return true if type == UID
    end
end

Upvotes: -2

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