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Home: Fun With Perl: Perl Quizzes - Learn Perl the Fun Way:



Jul 18, 2000, 8:44 AM

Post #1 of 4 (13800 views)
Return Can't Post

Are the 2 subroutines equivalent? Explain your answer.

sub new {

sub new {
return wantarray ? () : undef



Jul 18, 2000, 9:28 AM

Post #2 of 4 (13800 views)
Re: Return [In reply to] Can't Post

If your question is what is the difference in what is returned, then the answer is the first subroutine returns nothing and the second returns undef.

If your question is what is the difference in performance, well then obviously the subroutine that uses wantarray will take slightly longer. That is because the ternary operator must be evaluated in conjunction with wantarray where as the first subroutine just returns to where it was called from.

As for what the second second subroutine does:

wantarray returns true if the context of the currently executing subroutine is looking for a list value. It returns false if it is looking for a scalar. My guess is since return is looking for a scalar (in this context) that undef is returned instead of the empty list.


Jul 18, 2000, 3:48 PM

Post #3 of 4 (13800 views)
Re: Return [In reply to] Can't Post

mckhendry - there's no indication as to the context of these two subroutines. As they stand, they are equivalent. return returns the empty list in list context, and undef in scalar context. In fact, the output of the deparser shows that return() and return () are really return +() -- that is, explicitly returning an empty list.

return on its own is really return wantarray ? () : undef.


Jul 25, 2000, 8:48 AM

Post #4 of 4 (13800 views)
Re: Return [In reply to] Can't Post

sub new {return}

sub new {return wantarray ? () : undef}

Are the 2 subroutines equivalent and the ANSWER IS YES.

return with NO ARGUMENTS is really return wantarray ? () : undef.

GOOD job japhy.



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