Question

Just started with Ruby, and got stuck up with inline edit constructs:

v1="SO"
print v1.gsub!(/\W/,"").reverse
v2="SO!!"
print v2.gsub!(/\W/,"").reverse

v1.gsub! results in nil. Why? v2.gsub! works.

Answer 1

The key here is that you’re using the mutating version of gsub, gsub!, which modifies the actual string it is called on. As for what it returns, the documentation says it best:

Performs the substitutions of String#gsub in place, returning str, or nil if no substitutions were performed.

You should either use the non-mutating version, gsub, if you don’t actually wish to modify the string it is called on:

print v2.gsub(/\W/, "").reverse

Or you can do the substitution before printing the variable:

v2.gsub!(/\W/, "")
print v2.reverse

Or, in Ruby 1.9, you can use tap:

print v1.tap { |v1| v1.gsub!(/\W/, "") }.reverse