Question

Why does chomp allow chaining but chomp! doesn’t? For example:

"HELLO ".chomp.downcase
#> hello
"HELLO ".chomp!.downcase
#> nil

Another interesting example:

"100 ".chomp.to_i
#> 100
"100 ".chomp!.to_i
#> 0

Any ideas why this behavior occurs on the string, and why nil.to_i returns 0?

Answer 1

From the fine manual:

chomp(separator=$/) → new_str

Returns a new String with the given record separator removed from the end of str (if present). If $/ has not been changed from the default Ruby record separator, then chomp also removes carriage return characters (that is it will remove \n, \r, and \r\n).

and for chomp!:

chomp!(separator=$/) → str or nil

Modifies str in place as described for String#chomp, returning str, or nil if no modifications were made.

So neither chomp nor chomp! do what you think they do. Observe:

>> s = '100 '
=> "100 "
>> s.chomp
=> "100 "
>> s
=> "100 "
>> s.chomp!
=> nil
>> s
=> "100 "

So neither one cares about trailing spaces unless you tell them to, they just strip off trailing EOLs by default.

'100 '.chomp! returns nil because that’s what the documentation says it does. No substitution was made so it returns nil.

Why does nil.to_i give you zero? Well, from the fine manual:

to_i → 0

Always returns zero.

That doesn’t leave much room for ambiguity or interpretation.

I think you’re actually after the strip family of methods rather than chomp:

• String#lstrip
• String#lstrip!
• String#rstrip
• String#rstrip!
• String#strip
• String#strip!

Those remove whitespace from the string.