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Ways of quoting

by Aaronrp (Scribe)
on May 14, 2020 at 23:16 UTC ( #11116792=perlmeditation: print w/replies, xml ) Need Help??

I knew that you could use :: to make sure that a package name wasn't used as a subroutine, but I didn't really understand what it did.

$ perl -MO=Deparse -e '$x = anything_could_go_here::' $x = 'anything_could_go_here'; -e syntax OK

Just like single quotes?

TIMTOWTDI I guess...

So we have

q{} '' => :: qw{} - (as in -bareword)

And of course

no strict; $x = bareword;

not to mention

"" and qq{} `` and qx{}

Somebody will tell me that I missed some, I'm sure.

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Re: Ways of quoting
by davido (Cardinal) on May 15, 2020 at 21:22 UTC

    I have to admit, I hate the idea of the trailing ::.

    If you're enumerating the ways to quote things in Perl, don't forget HERE docs:

    <<HERE # Double quoted <<"HERE" # Double quoted, explicit. <<'HERE' # Single quoted, explicit. <<\HERE # Single quoted, uncommonly used. <<`HERE` # Same as qx or ``. <<~HERE # Double quoted, indented. <<~"HERE" # Double quoted, indented. <<~'HERE' # Single quoted, indented. <<~\HERE # Single quoted, indented, uncommonly used (I'll b +et you could grep all of CPAN and not find this). <<~`HERE` # Same as qx / ``, indented.

    Which made me think, too bad we don't have:

    <<~/HERE/x # Regexp object, indented, multi-line freeform (/ +x modifier).


      too bad we don't have: <<~/HERE/x
      my $re = qr/@{[<<'HERE']}/x; f . . HERE

      Close enough? ;-)

        Good enough for an upvote. I tend to shun the "@{[...]}" trick in real code, but this is a creative enough solution it made me smile.


Re: Ways of quoting
by LanX (Cardinal) on May 15, 2020 at 00:30 UTC

    IMHO the only purpose of assigning a package's name to a scalar is to handle it later in a referential or symbolic way.

    For instance $x->can("function") will return a code ref if "function" exists in the package.

    So the benefit of writing $x = anything_could_go_here:: over $x = 'anything_could_go_here' is only catching the error when misspelling the package's name.

    (you already demonstrated this after activating warnings )

    I'd strongly discourage using this as golfing hack to avoid single quotes around normal strings.

    Cheers Rolf
    (addicted to the Perl Programming Language :)
    Wikisyntax for the Monastery

      Yeah, clearly just using it as a sneaky way of quoting doesn't work.

      Having said this, one thing I've done in the past is something like this:

      use Const::Fast; use A::Really::Long::Class::Name::To::Type; const my $CLASS => 'A::Really::Long::Class::Name::To::Type'; $CLASS->do_something; $CLASS->do_something_else; $CLASS->yet_another_thing; # # and a bunch more of these #

      In that circumstance, seems to me that

      const my $CLASS => A::Really::Long::Class::Name::To::Type::;

      might actually be preferable, in that it gives you that check against the package name.

      All I can say is I've been using perl since the '90s and I still have so much I don't know.

Re: Ways of quoting
by kcott (Bishop) on May 15, 2020 at 07:39 UTC

    G'day Aaronrp,

    "I knew that you could use :: to make sure that a package name wasn't used as a subroutine, but I didn't really understand what it did."

    Take a look at "perlobj: Invoking Class Methods". I think that has the information you're missing.

    "Somebody will tell me that I missed some, I'm sure."

    You missed some. :-)

    "perlop: Quote and Quote-like Operators" has a list. The remainder of that section, and the following two sections, have details.

    — Ken

Re: Ways of quoting
by Aaronrp (Scribe) on May 15, 2020 at 00:05 UTC
    Serves me right.
    $ perl -MO=Deparse -we '$x = anything_could_go_here::' Bareword "anything_could_go_here::" refers to nonexistent package at - +e line 1. Name "main::x" used only once: possible typo at -e line 1. BEGIN { $^W = 1; } $x = 'anything_could_go_here'; -e syntax OK
    So, not exactly the same as single quotes.

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