use Perl

In code which sometimes returns 'false', I keep seeing code like the following:

sub foo {
  return undef unless bar(@_);   # or 'return 0;'
  return $something_else;
}

That behavior needs to be documented very carefully as it has a subtle bug which people keep stumbling over. Most of the time it works:

if ( my $result = foo() ) { ... }

But what if, for example, you want to accumulate results so you decide to use an array?

if ( my @results = foo() ) { ... }

Congrats! If &foo return false, you now have a one-element array which, in this context, evaluates as true. This is very likely a bug. You can accomplish the same thing, probably bug free, if you just use a bare return:

sub foo {
  return unless bar(@_);
  return $something_else;
}

From perldoc -f return:

If no EXPR is given, returns an empty list in list context, the undefined value in scalar context, and (of course) nothing at all in a void context.

In other words, if you wish to return 'false', a bare return will Do The Right Thing.

The only significant objection this I can recall hearing is the following:

if ( some_func(1, foo(), 2) ) { ... }

Because that's in list context, if &foo has a bare return, &foo returns the empty list and &some_func receives (1, 2). I don't see this happening too often, but you can get around it by forcing scalar context.

if ( some_func(1, scalar foo(), 2) ) { ... }

Now &some_func will receive (1, undef, 2).

Also, if you're returning from a ternary operator, you can get the same behavior with this:

return $some_val ? $some_val : ();