G'day perldigious,

This is to address a number of points in this branch of the thread; in particular, versions, features, warnings and interpolating postfix dereferencing within strings.

Firstly, starting with v5.24:

$ perl -v | head -2 | tail -1
This is perl 5, version 24, subversion 0 (v5.24.0) built for darwin-th
+read-multi-2level
[download]

This code recognises postderef syntax outside of strings but not within strings:

#!/usr/bin/env perl -l

use strict;
use warnings;

my $x = [qw{test string}];

print $x->@*;
print "$x->@*";
[download]

Output:

teststring
ARRAY(0x7fc63c005498)->@*
[download]

Adding either of these:

use 5.024;
[download]

or

use feature qw{postderef_qq};
[download]

Allows interpolation within strings:

Output:

teststring
test string
[download]

Now looking at v5.20.

$ perl -v | head -2 | tail -1
This is perl 5, version 20, subversion 0 (v5.20.0) built for darwin-th
+read-multi-2level
[download]

Output using the same initial code as before:

Array found where operator expected at ./pm_1174734_postderef.pl line 
+11, at end of line
    (Missing operator before ?)
syntax error at ./pm_1174734_postderef.pl line 11, near "->@*"
Execution of ./pm_1174734_postderef.pl aborted due to compilation erro
+rs.
[download]

To make this work, you need to turn off the experimental warnings (after the use warnings line) and use both the postderef and the postderef_qq features.

use warnings;
no warnings qw{experimental::postderef};
use feature qw{postderef postderef_qq};
[download]

Using the code and version shown, this outputs:

teststring
test string
[download]

Specifying a minimum version in the code, but running with a lesser version, gives:

Perl v5.20.0 required--this is only v5.18.0, stopped at ...
BEGIN failed--compilation aborted at ...
[download]

This tells you how to fix but not why.

Not specifying the version, gives:

Unknown warnings category 'experimental::postderef' at ...
BEGIN failed--compilation aborted at ...
[download]

This provides the why but not the how (i.e. you'll need some research to determine if that's a valid category and, if so, at what version it was introduced).

I prefer to specify the version. You may have a different preference or, perhaps, might be guided by in-house coding standards.

See also:

• perl5200delta: Experimental Postfix Dereferencing
• perldelta: Postfix dereferencing is no longer experimental [Correct at time of writing; current stable version 5.24; will refer to a different delta in future versions.]
• perl52400delta: Postfix dereferencing is no longer experimental [Dead link at time of writing; current stable version 5.24; expected to be a valid link in future versions.]
• use; feature; perlexperiment.
• CPAN pragma: experimental
• CPAN pragma: experimentals

Updates:

• change of meaning: s{expected to be a dead link}{will refer to a different delta}
• additional doco: Added manpage names to links: perldelta & perl52400delta

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