From: "Derrick B." <lists@...>
Date: 2012-12-20T06:45:51+09:00
Subject: Perl to Ruby: regex captures to assignment.

Hello all,

I am converting a Perl program to Ruby in order to learn Ruby.  There is
an expression that takes a string, ("1 3/4" or "5", for example)
determines what kind of fraction was entered, and assigns variables (w,
n, d), appropriately.  If a whole number was entered, then it assigns
the variables differently, of course.

The expression first checks for the presence of a slash ("/") to
determine if it is a fraction or whole number.  Then, using the
conditional operator, assigns the variables, appropriately.

Here are the two expressions:

Perl:

    my ($w, $n, $d) = ( $frac_str =~ /\// )
            ? $frac_str =~ /(?:(\S+) )??(\S+)\/(\S+)/
            : ( 1, $frac_str, 0 );

Ruby:

    w, n, d = frac_str.match(/\//) \
        ? frac_str.match(/(?:(\S+) )*?(\S+)\/(\S+)/).captures \
        : 0, frac_str, 1
    puts "w: #{w}, n: #{n}, d: #{d}"  # check assignment


I used irb to test the regex and it works just fine:

exp = Regexp.new(/(?:(\S+) )*?(\S+)\/(\S+)/)
=> /(?:(\S+) )*?(\S+)\/(\S+)/

str = "1 3/4"
=> "1 3/4"

n, w, d = str.match(exp).captures
=> ["1", "3", "4"]

w
=> "3"

n
=> "1"

d
=> "4"

But, the above version outputs:

w: 134, n: 1 3/4, d: 1

It appears to recurse over the regex and duplicate the captures.  But,
since I am new to this language, I know I can use an 'if..else'
statement, but since I am coming from Perl, I figured that a similar
expression would "just work"!  :)

Thanks for your time and input,

Derrick

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