From: Josh Cheek <josh.cheek@...>
Date: 2011-04-04T18:58:40+09:00
Subject: Re: pipe question

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On Sun, Apr 3, 2011 at 10:42 PM, Josh Cheek <josh.cheek@gmail.com> wrote:

> 1) In Ruby, false and nil are treated as falsy. Everything else is treated
> as truthy.
>
> "truthy" if nil         # => nil
> "truthy" if false       # => nil
> "truthy" if true        # => "truthy"
> "truthy" if "str"       # => "truthy"
> "truthy" if 1           # => "truthy"
> "truthy" if 1.23        # => "truthy"
> "truthy" if /regex/     # => nil
> "truthy" if :symbol     # => "truthy"
> "truthy" if 'r'..'ange' # => "truthy"
>
>
I just listed out a bunch of examples and then ran them.... But I'm looking
now, and realize that /regex/ evaluated as falsy!  After some playing
around, I have decided that it is based on Perl. If you put a regex in a
variable, it treats it as a boolean "is it an object?" and behaves as I
stated previously. But if you put it in a literal, it plays Perl and checks
to see if it matches against $_

regex = /re(.)ex/
$_                    # => nil

# in literal, so checks if it matches $_
# (note that it warns: regex literal in condition)
"truthy" if /re(.)ex/ # => nil

# in var, so checks if it exists
"truthy" if regex     # => "truthy"

# explicitly set $_, now literal matches
$_ = "reGex"
"truthy" if /re(.)ex/ # => "truthy"

# when we look at capture group, we see the G we made
$1                    # => "G"

# change the $_ to see if variable matches it
$_ = "reXex"
"truthy" if regex     # => "truthy"

# nope, it should be "X" if it matched.
$1                    # => "G"

# just to double check
$1 if /re(.)ex/       # => "X"


So, regex aren't nil or false, and are thus truthy. But when you throw a
regex literal in the conditional, it does some implicit operations and
doesn't pass the regex straight on through to the conditional.

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