use strict;
use warnings;
use Excel::Writer::XLSX;

my $file = (@ARGV) ? 'perl_bug.xlsx' : 'perl_good.xlsx';
my $book = Excel::Writer::XLSX->new($file);
my $worksheet = $book->add_worksheet();
$worksheet->write( 0, 0, 'Hi Excel!' );
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Thanks, but the code I posted was not written to be the most concise and direct way to perform a task. It was written to demonstrate the error that I found. It may be oddly structured as a result. The choice of file names is really secondary to the problem.

use strict;
use Excel::Writer::XLSX;

&func(@ARGV);
{
    my $closure_workbook;
    
    sub func {
        my $file = 'perl.xlsx';
        my $book = Excel::Writer::XLSX->new($file);
        if (@_) {
            $closure_workbook = $book;
        }
        my $worksheet = $book->add_worksheet();
        $worksheet->write(0, 0, 'Hi Excel!');
    }
}
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People seem to be misunderstanding the point of my question. If you look at this code, you can see that there is a single line that may optionally be executed: the line that assigns $book to the static variable $closure_workbook. It's not worth explaining why, but I want to store $book in a static variable. And I see no reason that the one extra assignment should cause an error.

use strict;
use Excel::Writer::XLSX;

&func(@ARGV);
{
    my $closure_workbook;
    
    sub func {
        my $file = 'perl.xlsx';
        my $book = Excel::Writer::XLSX->new($file);
        if (@_) {
            $closure_workbook = $book;
        }
        my $worksheet = $book->add_worksheet();
        $worksheet->write(0, 0, 'Hi Excel!');
    }
}
[download]

If you look at this code...

By "this code", I assume you mean the code posted at the end of the Re^2: variable scopes in Excel::Writer::XLSX node, and that this code is all that is needed to produce the error you describe. (I'm not in a position right now to run the code; all I can do is literally 'look' at it.)

... I see no reason that the one extra assignment should cause an error.

Nor do I. The  $closure_workbook variable is never touched except to assign it a value in certain circumstances. It is never otherwise accessed within  func() and no other function than  func() can possibly access this lexical variable (unless there's something you're not showing us). The next step is to eliminate the
    if (@_) {
        $closure_workbook = $book;
    }
block of code (leaving the  my $closure_workbook; statement just for grins) and see if the error still occurs. My bet is it will. This means the root cause of your problem is entirely unconnected to anything you're doing with this 'closure' variable.

For a while, I had my suspicions about the  &func(@ARGV); ampersand invocation of  func(), but I can't see this has any relevance.

Update: Oops... Should have refreshed the thread before posting. I see from Re^4: variable scopes in Excel::Writer::XLSX that the problem is resolved. At any rate, the problem had, indeed, nothing to do with anything that was happening with the 'closure' variable.

People seem to be misunderstanding the point of my question..
Because what you intended is not clear. Closures in perl are not written like that. And you must have reason for what you are doing. You are calling a variable that is outside a function within the function, to assign to it an object. To what end? Oh I just want to call it. Is that not funny? Please take a look at the various suggestions already given. The solutions you wanted might be somewhere in the middle, if not already given.

Hi johnrcomeau,
Really, I can't figure what you really wanted to use, however you can use this: [the code below actually works]

use warnings;
use strict;
use Excel::Writer::XLSX;

func(@ARGV);

sub func {
    my $file      = 'perl.xlsx';
    my $book      = Excel::Writer::XLSX->new($file);
    my $worksheet = $book->add_worksheet();
    my $closure_workbook;
    if (@_) {
        $closure_workbook = sub {
            $worksheet->write_col( 0, 0, [@_] );
        };
        return $closure_workbook->(@_);
    }
    else {
        $worksheet->write( 0, 0, 'Hi Excel!' );
    }

}
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