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dvdrtrgn on 08/19/08

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The equals greater than operands

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<pre>
Tiffany S. (NiceTiff...@webtv.net) wrote:

: What do the symbols => and -> mean?  I can find them used in scripts,
: but I can't find them explained in either books or online.

Without even knowing the language it's hard to give a correct answer.

But I'll guess your using perl.

First, if indeed perl is the language, then the answer most certainly is
available online, you just need to know what to read.

If you have perl installed then type
        perldoc perlsyn
        perldoc perlop

If you don't have perl installed then type the above into google instead,
or google something like "perl" "operators"

Anyway, in perl, => is a special type of comma.  It's used like a comma
but the thing on the left is automatically quoted (basically).

so
        ("one","two")   is similar to   (one=>"two")

And -> means "points to".  It's taken from C notation and has a similarish
meaning.  If, instead of a plain old variable that contains a value, you
instead have a variable that _references_ another variable, then you can't
get the value directly because it isn't kept "in" the variable.  Instead
the variable "points to" where the value is kept.  Read the doc for
details.

so you will see things like

$x[0]   # first element of an array called "x"

$x->[0]      # first element of an array, but the array is _not_ called
                # "x".  Instead the array is kept somewhere else, and
                # the variable "x" _points to_ where the array is being
                # kept.

<hr>

Tiffany S. wrote:
> What is the explanation of the => and the -> operands? I've run
> across them, but can't find anything about them in tutorials or
> reference manuals.

=> can be used in place of a comma, and is commonly used to separate
key/value pairs when creating a hash.

my %hash = (dog, 'bark',
             cat, 'meow',
             cow, 'moo',
             pig, 'oink'
            );

can be written as:

my %hash = (dog => 'bark',
             cat => 'meow',
             cow => 'moo',
             pig => 'oink'
            );

The => simply makes it easier to read.

If, instead, I had written:

my $hash = {dog => 'bark',
             cat => 'meow',
             cow => 'moo',
             pig => 'oink'
            };

(note the curly brackets instead of parentheses) then $hash would
contain a reference to a hash. I would have to dereference the hash to
access any of the values for a given key.

I could

print $$hash{dog};

or I could

print $hash->{dog};

If you are not familiar with references, look here:
http://perldoc.perl.org/perlreftut.html
</pre>

URL: http://groups.google.com/group/comp.infosystems.www.authoring.cgi

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