no implicit conversion of nil into String when using hash without =>

Question

my program works fine with this hash

hash = 
    {
    'keyone'=> 'valueone',
    'keytwo'=> 'valuetwo',
    'keythree'=> 'valuethree'
    }

but someone pointed out the this notation is old and that now I should use:

  hash = 
        {
        'keyone': 'valueone',
        'keytwo': 'valuetwo',
        'keythree': 'valuethree'
        }

I get this error:

no implicit conversion of nil into String (TypeError)

I only changed the hash notation. Can someone explain what is happening?

For non symbol keys, you must use `=>`. See [mu's](https://stackoverflow.com/a/10004344/5025116) answer. — Sebastián Palma, Dec 12 '17 at 12:18
_"my program works fine with this hash"_ – despite the missing commas? — Stefan, Dec 12 '17 at 12:22
@Stefan Sorry, I forgot to write the commas here, but I have them in my code xD — Tiago Mateus, Dec 12 '17 at 12:26

score 2 · Accepted Answer · edited Dec 12 '17 at 13:23

2

In the latter your keys are saved as symbols. So you should refer to them as:

hash[:keyone]

And if symbols are just fine, this is even better

hash = {
  keyone: 'valueone',
  keytwo: 'valuetwo',
  keythree: 'valuethree'
}

But, if you need string keys, you have to stick with the "old" syntax

hash = {
  'keyone' => 'valueone',
  'keytwo' => 'valuetwo',
  'keythree' => 'valuethree'
}

edited Dec 12 '17 at 13:23

Chivorn Kouch

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answered Dec 12 '17 at 12:20

Ursus

29,643
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score 2 · Answer 2 · answered Dec 12 '17 at 12:36

2

I only changed the hash notation.

No, you didn't. You also changed the type of the key objects from Strings to Symbols.

{ 'key': 'value' }

is not equivalent to

{ 'key' => 'value' }

it is equivalent to

{ :key => 'value' }

answered Dec 12 '17 at 12:36

Jörg W Mittag

363,080
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score 0 · Answer 3 · answered Dec 12 '17 at 12:21

The new notation uses symbols for keys:

hash = {
    keyone: 'valueone',
    keytwo: 'valuetwo',
    keythree: 'valuethree'
}
puts hash
# {:keyone=>"valueone", :keytwo=>"valuetwo", :keythree=>"valuethree"}

Your code also misses the commas between the items.

no implicit conversion of nil into String when using hash without =>

3 Answers3