Re: Explaining why to use $array[0] instead of @array[0]

G'day David,

DavidB wrote:
> Hi, I can think of some reasons we use $ instead of @ for array
> indices (in Perl5):

My usual explanation goes a little like this:

In Perl, $ is pronounced 'the' or 'a' or 'this' (ie, singular):

	$name			# The name
	$friend[0]		# The first friend
	$colour_of{grass}	# The colour of grass
	$ref->{$key}		# The value $key using this reference.

On the other hand, @ means 'these' or 'those':

	@friend			# These friends
	@friend[0..3]		# These four friends

When we write an @ sign when trying to retrieve a single element, we're
really asking Perl for a list of elements.  If what we really want back is
just a single element, then Perl can get confused.

I don't actually show the cases where Perl gets it wrong, instead I mention
that Perl:

	(a) Will warn you if it figures out that you wanted a scalar when
	    you asked for a list.

	(b) Will *not* warn you when it decides you actually meant a list
	    of one element.  This means debugging your code will be a
	    painful experience, because Perl won't help you.

Hence the result of using @ incorrectly is almost always a warning or a
hard-to-find bug, both of which are extremely undesirable.

Cheerio,

	Paul

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Paul Fenwick <[email protected]> | http://perltraining.com.au/
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