I'm getting an unexpected return value with this code:
str = ''; 'abc'.chars.map {|c| str<<c}
Expected output:
["a", "ab", "abc"]
Actual output:
["abc", "abc", "abc"]
Adding a puts(str) for debugging:
str = ''; 'abc'.chars.map {|c| puts(str); str<<c}
a
ab
=> ["abc", "abc", "abc"]
Why is the above code not returning the expected output? Thanks.
From the fine manual:
string << object → string.
Concatenatesobjecttoselfand returnsself
So str << c in the block alters str and then the block itself evaluates to str.
You could say this to get the results you're after:
str = ''
'abc'.chars.map { |c| (str << c).dup }
str multiple times. I needed dup to create a different object on each iteration.
dup necessarily, you could also create new objects by re-assigning str, e.g. 'abc'.chars.map { |c| str = "#{str}#{c}" }It's because each element in your map is returning a reference to str's value, not the actual value of str. So your map is returning 3 references to the value of str and not the value of str at the time of iteration; because each reference to str points to one place in memory at the end that has 'abc', that's why you see the final value of str 3 times.
# frozen_string_literal: truedirective. It will prevent you from using destructive methods likeString#<<. There is a performance penalty in some scenarios, but the tradeoff is worth it for most teams.