On Jan 13, 2011 2:24 AM, "Uri Guttman" <u...@stemsystems.com> wrote:
>
> >>>>> "sw" == shawn wilson <ag4ve...@gmail.com> writes:
>
> >> subs in perl ALWAYS return something, either the value from return or
> >> the last evaluated expression.
>
> sw> What do you mean by this?
>
> sw> sub nothing {
> sw> my $something = 5;
> sw> if ( $something == 5) {}
> sw> }
>
> sw> ... will return 'undef' and not 5 or anything else, right?
>
> from perldoc perlsub:
>
> A "return" statement may be used to exit a subroutine, optionally
> specifying the returned value, which will be evaluated in the
> appropriate context (list, scalar, or void) depending on the context
of
> the subroutine call. If you specify no return value, the subroutine
> returns an empty list in list context, the undefined value in scalar
> context, or nothing in void context. If you return one or more
> aggregates (arrays and hashes), these will be flattened together
into
> one large indistinguishable list.
>
> If no "return" is found and if the last statement is an expression,
its
> value is returned. If the last statement is a loop control structure
> like a "foreach" or a "while", the returned value is unspecified.
The
> empty sub returns the empty list.
>
> i never said subs return something useful but something is always
> available to the caller on the stack. this is one (of many) reasons i
> say to (almost) always use explicit returns. it guarantees you know what
> you are returning, it tells the reader what is being returned and it
> avoids bugs. one classic bug is some code that returns the last
> expression and someone adds code after that breaking the return. another
> bug is when the last statement is some compound thing like if/else and
> it may return the right thing but it is hard to tell what is going
> on. and as the docs say a loop control will be unspecified in what it
> returns. so use explicit return statements to avoid all of these
> issues. simple and important.
>
> there are some special cases where no return statement may be better. i
> won't go into those now.
>
I dig what you're saying about always using return. However I don't (have
never used / seen) a case where a sub returns last expression. An example
maybe?
