Re: Multi-line comments in perl code?

[rodion]

in reply to Multi-line comments in perl code?

I think it's useful to boil down what's already been said or referred to.

• POD is the official way to do multi line comments in Perl, whether you think of it as as a work-around or not (which varies),
• use "=for comment" or "=begin/end comment" for stuff that's just comments and shouldn't show up in the output text when documentation is extracted from the code, such as when you run perldoc on the program,
• You can't indent the "=for comment", so it's not quite like other language's multiline comments, and
• You do need a "=cut" at the end to get back to code. (I think this might be your main objection to using POD, and, yes, you're stuck with it).

The last item may change with Perl6, for "=begin/end", but the rest will probably not. See Apocalypse 2 RFC 5

Here's an example which you can runn with "perl" and with "perldoc" to see what shows up where. Note that in many places, such as before the "=cut", the blank line is part of the syntax.

=head1 tstcmt.pl

This is text that shows up with the "perldoc tstcmt.pl" 
command. The comment sections below do not.

=cut

print "hello\n";

=for comment 
This is a single paragraph of comment text, spanning
multiple lines. It ends with the first blank line.
After that, the text is inuded with other printed pod text
that shows up with perldoc

This text also shows up with perldoc, it's not part of 
the "for" comment above.

=cut

print "hello1\n";

=for comment 
Another paragraph of comment text, spanning
multiple lines. It ends with the first blank line.

=cut

print "hello2\n";

=begin comment
This is a multi-paragraph comment section.
Which is terminated by an =end comment on a line by itself.

This is a second paragraph

=end comment

=cut

print "hello3\n";

=head2 Other pod documentation

This is text that also shows up with the "perldoc tstcmt.pl" 
command. The comment sections above do not.

=cut

print "hello4\n"

[Anonymous Monk]

Also you can always look at another Perl module and see how they document their code :)

[TheDamian]

The last item may change with Perl6, for "=begin/end", but the rest will probably not.

Actually, the first point:

POD is the official way to do multi line comments in Perl

will also change in Perl 6, which introduces an indentable, nestable, multi-line-able delimited comment:

    #{ comment 
       here 
     }
    #[ comment 
       here 
     ]
    #( comment here )
    #< comment here >
    #« comment etc. »

A delimited comment is introduced by a # followed immediately by any kind of opening bracket. It is closed by the corresponding closing bracket.

[jdporter]

Ow. Would it be too much to ask that it accept any sequence of openingbrackets — e.g.

#<<<
#<{[

because I could easily see myself wanting to comment out blocks of code with unbalanced closing brackets of all four types (or, more to the point, a dynamic selection of closing bracket types). Having an unlimited variety of comment "identifiers" also facilitates arbitrarily nesting comments without artificial restrictions.

[marklark]

If I read it correctly, Damian said, "It is closed by the corresponding closing bracket." [Emphasis added]

So, the compiler ignores the non-corresponding closing brackets.

[TheDamian]

Ow. Would it be too much to ask that it accept any sequence of opening brackets

Not to much to ask at all. At least, not as long as you can be satisfied with multiple repetitions of the same delimiter character. From the latest update of Synopsis 2:

• For all quoting constructs that use user-selected brackets, multiple, adjacent, identical opening brackets must always be matched by an equal number of adjacent closing brackets. Bracket counting naturally applies only to sets of brackets of the same length:

      say #{{
          Comment contains unmatched } and { { { { plus a counted {{ ... }} pair.
      }} q<< <<woot>> >>   # says "<<woot>>"

[BrowserUk]

Yay!++