Are quotes around hash keys a good practice in Perl?

Question

Is it a good idea to quote keys when using a hash in Perl?

I am working on an extremely large legacy Perl code base and trying to adopt a lot of the best practices s

Answer 1

I don't think there's a best practice on this one. Personally I use them in hash keys like so:

$ident{'name'} = standardize_name($name);

but don't use them to the left of the arrow operator:

$ident = {name => standardize_name($name)};

Don't ask me why, it's just the way I do it :)

I think the most important thing you can do is to always, always, always:

use strict;
use warnings; 

That way the compiler will catch any semantic errors for you, leaving you less likely to mistype something, whichever way you decide to go.

And the second most important thing is to be consistent.

Answer 2

Go with the quotes! They visually break up the syntax and more editors will support them in the syntax highlighting (hey, even Stack Overflow is highlighting the quote version). I'd also argue that you'd notice typos quicker with editors checking that you ended your quote.

Answer 3

It is better with quotes because it allows you to use special characters not permitted in barewords. By using quotes I can use the special characters of my mother tongue in hash keys.

Answer 4

I never single-quote hash keys. I know that {} basically works like quotes do, except in special cases (a +, and double-quotes). My editor knows this too, and gives me some color-based cues to make sure that I did what I intended.

Using single-quotes everywhere seems to me like a "defensive" practice perpetrated by people that don't know Perl. Save some keyboard wear and learn Perl :)

With the rant out of the way, the real reason I am posting this comment...the other comments seem to have missed the fact that + will "unquote" a bareword. That means you can write:

sub foo {
    $hash{+shift} = 42;
}

or:

use constant foo => 'OH HAI';
$hash{+foo} = 'I AM A LOLCAT';

So it's pretty clear that +shift means "call the shift function" and shift means "the string 'shift'".

I will also point out that cperl-mode highlights all of the various cases correctly. If it doesn't, ping me on IRC and I will fix it :)

(Oh, and one more thing. I do quote attribute names in Moose, as in has 'foo' => .... This is a habit I picked up from working with stevan, and although I think it looks nice... it is a bit inconsistent with the rest of my code. Maybe I will stop doing it soon.)

Answer 5

I've always used them without quotes but I would echo the use of strict and warnings as they pick out most of the common mistakes.

Answer 6

When specifying constant string hash keys, you should always use (single) quotes. E.g., $hash{'key'} This is the best choice because it obviates the need to think about this issue and results in consistent formatting. If you leave off the quotes sometimes, you have to remember to add them when your key contains internal hypens, spaces, or other special characters. You must use quotes in those cases, leading to inconsistent formatting (sometimes unquoted, sometimes quoted). Quoted keys are also more likely to be syntax-highlighted by your editor.

Here's an example where using the "quoted sometimes, not quoted other times" convention can get you into trouble:

$settings{unlink-devices} = 1; # I saved two characters!

That'll compile just fine under use strict, but won't quite do what you expect at runtime. Hash keys are strings. Strings should be quoted as appropriate for their content: single quotes for literal strings, double quotes to allow variable interpolation. Quote your hash keys. It's the safest convention and the simplest to understand and follow.