On Sat, Jun 13, 2009 at 07:30, John W. Krahn<jwkr...@shaw.ca> wrote: > Chas. Owens wrote: >> >> On Sat, Jun 13, 2009 at 03:48, John W. Krahn<jwkr...@shaw.ca> wrote: >>> >>> Chas. Owens wrote: >>>> >>>> On Fri, Jun 12, 2009 at 20:24, Steve Bertrand<st...@ibctech.ca> wrote: >>>>> >>>>> my $hours_used = ($hours_lookup->get_month_hours($dbh, $username, >>>>> $search_date, 'dialup')); >>>> >>>> Why are you creating a list here? Just say >>> >>> Do you mean the list ($dbh, $username, $search_date, 'dialup')? I think >>> that is required for the function to work correctly. Otherwise there is >>> no >>> other list there, the external parentheses are superfluous and do not >>> define >>> a list. A scalar rvalue enclosed in parentheses is just a scalar value. >> >> No, it is a list of one item, > > perldoc perlfunc > [ snip ] > Remember the following important rule: There is no rule that relates > the behavior of an expression in list context to its behavior in > scalar context, or vice versa. It might do two totally different > things. Each operator and function decides which sort of value it > would be most appropriate to return in scalar context. Some > operators return the length of the list that would have been > returned in list context. Some operators return the first value in > the list. Some operators return the last value in the list. Some > operators return a count of successful operations. In general, they > do what you want, unless you want consistency. > > A named array in scalar context is quite different from what would > ^^^^^^^^^^ > at first glance appear to be a list in scalar context. You can’t > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^ > get a list like "(1,2,3)" into being in scalar context, because the > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > compiler knows the context at compile time. It would generate the > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > scalar comma operator there, not the list construction version of > the comma. That means it was never a list to start with. > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > > perldoc perlfaq4 > [ snip ] > Data: Arrays > What is the difference between a list and an array? > > An array has a changeable length. A list does not. An array is > something you can push or pop, while a list is a set of values. > Some people make the distinction that a list is a value while an > array is a variable. Subroutines are passed and return lists, you > put things into list context, you initialize arrays with lists, and > you foreach() across a list. "@" variables are arrays, anonymous > arrays are arrays, arrays in scalar context behave like the number > of elements in them, subroutines access their arguments through the > array @_, and push/pop/shift only work on arrays. > > As a side note, there’s no such thing as a list in scalar context. > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > When you say > > $scalar = (2, 5, 7, 9); > > you’re using the comma operator in scalar context, so it uses the > scalar comma operator. There never was a list there at all! This > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > causes the last value to be returned: 9. > > >> which in scalar context yields the last > > There is no such thing as a list in scalar context (see above.) > >> item (which also happens to be the only item) just like any other >> list. You are correct that they are superfluous, that is why I am >> asking him why he is bothering to create the list with them. > > Parentheses do not create a list, they are used to define precedence. > > >> If the parentheses did not create a list then this code >> >> my $undef = (); >> >> Would produce an error because there is no scalar value to assign to >> $undef. Instead, () is a list of no items which yields an undef in >> scalar context. There is nothing magical about > > There is no such thing as a list in scalar context (see above.) > > >> my $scalar = (1); >> >> that makes (1) not a list but a scalar instead, it follows the exact >> same rules as all other lists: yield your last element in scalar >> context. This is roughly the same as > > There is no such thing as a list in scalar context (see above.) > > >> my $s = @a[0]; >> >> It works, but is probably not what you meant to say. > > > > > John > -- > Those people who think they know everything are a great > annoyance to those of us who do. -- Isaac Asimov > > > -- > To unsubscribe, e-mail: beginners-unsubscr...@perl.org > For additional commands, e-mail: beginners-h...@perl.org > http://learn.perl.org/ > > >
Alright, I concede my understand was flawed. -- Chas. Owens wonkden.net The most important skill a programmer can have is the ability to read. -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
