'A val that is guaranteed not to be present in any list'
ow! Please use out-of-band signaling. Safer, Simpler, Prettier.
Method 1, return value + lvalue param:
my $fetch = sub {
my ($fh) = @_;
return if eof $fh;
$_[1] = scalar <$fh>;
return 1;
};
...
while ($next->(my $item)) {
print "$item\n";
}
Method 2, undef vs reference:
my $fetch = sub {
my ($fh) = @_;
return if eof $fh;
return \(scalar <$fh>);
};
...
while (my $ref = $next->()) {
print "$$ref\n";
}
Method 3, empty list vs non-empty list (like each):
my $fetch = sub {
my ($fh) = @_;
return if eof $fh;
return scalar <$fh>;
};
...
# RIGHT: while (my ($item) = $next->())
# WRONG: while (my $item = $next->())
while (my ($item) = $next->()) {
print "$item\n";
}
Update: Added second and third method.
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