In Perl 5.6.1 and later, there are some quite strict compile-time checks on the return value from an lvalue subroutine. Because the checks are done at compile-time, it doesn't matter if you know at run-time that you're going to be in lvalue context.
So code like:
sub foo :lvalue {
if (want('RVALUE')) {
return 23;
} else {
$foo;
}
}
won't even compile. The new version of Want adds a function rreturn which you can use for an rvalue return from an lvalue sub. So the above can be written as:
sub foo :lvalue {
if (want('RVALUE')) {
rreturn 23;
} else {
$foo;
}
return;
}
The compiler sadly doesn't realise that rreturn will actually return from the function, so you have to put the bare return; at the end to shut it up. But you can think of that like the 1; that you have to put at the end of a module: meaningless furniture that has to be there.
Actually, the check is obviously too strict, because something like:
sub foo :lvalue {
if (something_bad()) {
die "Something bad happened";
} else {
$foo;
}
}
ought to be okay. But in Perl 5.6.1 it won't compile. Can't modify die in lvalue subroutine return. I'm not trying to modify it, you brain-damaged compiler!
