Yes, Internals::SvREADONLY is there all right:

 1:35 >perl -E "say for sort keys %Internals::"
SvREADONLY
SvREFCNT
V
hv_clear_placeholders

 1:35 >

[download]

But it doesn’t work for me. A Windows issue, maybe?

Thanks for the information on where to find the Internals package in the source code.

Update: I tried the Internals module, but that doesn’t work (for me, on Windows) either:

#! perl
use strict;
use warnings;
use Internals qw(SetReadWrite);

for (qw(literal1 literal2 literal3))
{
    print "$_\n";
    foo('wilma');
}

sub foo
{
    SetReadWrite(\$_);
    $_ = 'fred';
    goto &bar;
}

sub bar
{
    my ($name) = @_;
    print "foo --> name = $name, \$_ = $_\n";
}

[download]

Output:

12:26 >perl 723_SoPW.pl
literal1
Modification of a read-only value attempted at 723_SoPW.pl line 15.

12:28 >

[download]

Even IsWriteProtected fails:

#! perl
use strict;
use warnings;
use Internals qw(IsWriteProtected);

for (qw(literal1 literal2 literal3))
{
    print "$_\n";
    foo('wilma');
}

sub foo
{
    if (IsWriteProtected(\$_))
    {
        warn "Can't modify \$_";
    }
    else
    {
        $_ = 'fred';
    }

    goto &bar;
}

sub bar
{
    my ($name) = @_;
    print "foo --> name = $name, \$_ = $_\n";
}

[download]

Output:

12:28 >perl 723_SoPW.pl
literal1
Modification of a read-only value attempted at 723_SoPW.pl line 20.

12:36 >

[download]

:-(

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

In reply to Re^6: How to safely use $_ in a library function? by Athanasius
in thread How to safely use $_ in a library function? by perl-diddler

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