perl: what does the hyphen in function call params mean?

johnMG · 08-19-2005, 03:28 PM

In Perl, what does that hyphen (dash, minus sign) mean when
placed before function arguments?

For example, used with PerlTk:

$menubar = $top->Frame->pack(-side => "top", -fill => "x");

I know that => is just a pretty comma :), but I've never seen the
hyphen usage explained anywhere.

Thanks,
---John

puffinman · 08-19-2005, 03:59 PM

It doesn't mean anything. In the => hash syntax, it is not only just a pretty comma, it also automatically quotes the expression on the left of the arrow. So the following lines are all equivalent:

Code:

$menubar = $top->Frame->pack(-side => "top", -fill => "x");
$menubar = $top->Frame->pack("-side" => "top", "-fill" => "x");
$menubar = $top->Frame->pack("-side", "top", "-fill", "x");

So the leading hyphen is nothing more than a character. I think it is just the choice of the programmer of the package you are using as to what to call the various options. With Tk it may just be for compatibility with non-Perl usage.

johnMG · 08-19-2005, 04:17 PM

Thanks puffinman!