[psyklic]

Interestingly, assignment inside conditionals is usually avoided because it is easy to accidentally do an assignment (=) rather than a comparison (==). Note that for multiple assignment this mistake can no longer happen:

  irb(main): a, b == 3
  SyntaxError: syntax error, unexpected ==, expecting '='

Should it still be avoided? :)

[jbackus]

First of all that is an interesting point. Given that it isn't as potentially dangerous I'll agree that it is less bad than I initially thought.

I'll respond to your question by asking you a question. Which of the following expressions evaluate to "truthy"?

    'truthy' if (a, b = [])              # =>
    'truthy' if (a, b = nil)             # =>
    'truthy' if (a, b = [nil])           # =>
    'truthy' if (a, b = [nil, nil])      # =>
    'truthy' if (a, b = [false])         # =>
    'truthy' if (a, b = [false, false])  # =>
    'truthy' if (a, b = [true, false])   # =>
    'truthy' if (a, b = [false, true])   # =>
    'truthy' if (a, b = *[])             # =>
    'truthy' if (a, b = *nil)            # =>
    'truthy' if (a, b = *[nil])          # =>
    'truthy' if (a, b = *[nil, nil])     # =>
    'truthy' if (a, b = *[false])        # =>
    'truthy' if (a, b = *[false, false]) # =>
    'truthy' if (a, b = *[true, false])  # =>
    'truthy' if (a, b = *[false, true])  # =>

The answer is in this gist: https://gist.github.com/backus/c9b70dee67470698fd7d4a66ddf03.... Don't peek!

[psyklic]

Good exercise! So it may still be too easy to misunderstand when exactly the condition will be true.