[Pdx-pm] the quest for return_if

Eric Wilhelm scratchcomputing at gmail.com
Tue Jun 26 17:57:19 PDT 2007

# from benh
# on Tuesday 26 June 2007 05:17 pm:

>Ideally I would love to do this:
>sub return_if {
>   my ($eval, $value) = @_;
>   $value = $eval if !defined($value);
>   {FROM_THE_POINT_WHERE_I_WAS_CALLED}->return $value if
> defined($eval); }

That's not exactly clear.  Are you trying to return the value if it is 
defined?  That is, you're trying to get away from two-line things like:

  my $val = answer($param);
  return($val) if(defined($val));


Yeah, that could be tighter, but I don't recall ever being bothered by 
it (then again, I'm not looking at ten pages of them, are you?)

The opposite is pretty concise:

  return() unless(defined(my $val = answer($param)));

>[colin]humm... goto looks like I could be worth a stab.

Probably want to avoid that.  Any goto besides gosub (goto &subname) is 
typically asking for trouble and gosub doesn't really apply here.

Sounds like you're asking for a macro of some sort.  Since this is not 
C, maybe try looking at it from a different POV.

If it is a big list of methods without any intermediate code, you could 
just do something like:

  foreach my $method (@methods) {
    my $val = $self->$method;
    return($val) if(defined($val));

You can do that with functions too, but you have to turn off strict or 
make @methods be a list of references to the functions (or anonymous 
subs with the values curried (curried?.))

  my @funcs = (
    sub {this_one($foo, @_)},
    sub {that_one($bar, @_)},
    sub {the_next($baz, $bar, $foo, @_)},
  foreach my $func (@funcs) {
    my $ans = $func->(@extra_params);
    return($ans) if(defined($ans));

Or use a source filter ;-)

Entia non sunt multiplicanda praeter necessitatem.
--Occam's Razor

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