How to create new functions for String class in Ruby?

Question

I want to check the type of strings that I encounter:

class String
    def is_i?
        /\A[-+]?\d+\z/ === self
    end

    def is_path?
        pn = Pathname.new(self)
        pn.directory?
    end     
end

def check(key)
    puts case key
    when is_i?
        puts "Could be a number"
    when is_path?
        puts "This is a path"
    else
        puts "Ok"
    end
end

When I run check("1345425") I get the following error:

undefined method `is_i?' for main:Object (NoMethodError)

What should I do to correct it?

Your check method is not defined on the String class but you're calling is_i? on it. Try writing when key.is_i? and when key.is_path? instead. — xea
– xea, Commented Oct 27, 2015 at 16:53
The methods you defined on string are fine. Your problem is you've misunderstood how case works. — Nathan
– Nathan, Commented Oct 27, 2015 at 16:58

Aleksei Matiushkin · Accepted Answer · 2015-10-27 16:56:06Z

2

You have defined functions on String instance, hence:

def check(key)
    puts case
         when key.is_i?
           "Could be a number"
         when key.is_path?
           "This is a path"
         else
           "Ok"
         end
end

or

def check(key)
    puts case key
         when ->(s) { s.is_i? }
           "Could be a number"
         when ->(s) { s.is_path? }
           "This is a path"
         else
           "Ok"
         end
end

UPD Please also note that I removed superfluous subsequent calls to puts.

answered Oct 27, 2015 at 16:56

Aleksei Matiushkin

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Comments

xea · Accepted Answer · 2015-10-27 16:57:47Z

1

Your check method isn't defined on the String class, so when you write when is_i? and when is_path? it is trying to call those methods on your main, hence the error.

You should call these methods on your String object (key) like this:

...
when key.is_i?
...
when key.is_path?
...

answered Oct 27, 2015 at 16:57

xea

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Comments

Thach Chau · Accepted Answer · 2015-10-27 17:01:33Z

0

You may change it like this

class String
  def is_i?
    /\A[-+]?\d+\z/ === self
  end

  def is_path?
    pn = Pathname.new(self)
    pn.directory?
  end
end

def check(hash_key)
  puts case hash_key
  when Proc.new { hash_key.is_i? }
    return "Could be a number"
  when Proc.new { hash_key.is_path? }
    return "This is a path"
  else
    return "Ok"
  end
end

Running check('1312312') in irb returns result as "Could be a number"

answered Oct 27, 2015 at 17:01

Thach Chau

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1 Comment

Aleksei Matiushkin Over a year ago

Please never use return in ruby like this.

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