Question

Possible Duplicate:
conditional statement and assigning value in ruby

While refactoring some rails code, I have encountered some syntax oddity in ruby.

Given the following method

def get_value
  42
end

Why does this work?

if value = get_value
  puts value
end

While this does not?

puts value if value = get_value

The latter gives an error: undefined local variable or method `value' for main:Object (NameError). I thought these expressions were equal? When the if-block is evaluated before the puts, value should not be undefined.

Answer 1

It’s due to the parsing of lines, vs execution time. In the first version, value is parsed and set and then the puts evaluated. In the second line, when the parser gets to the variable puts value, it has not yet been defined. In other words, it can’t run the line to set the variable, until it has first parsed the line.