Hi lee, I should note that it is my impression that you are far too needy in your enquiring, and I'm starting to lose patience.
On Mon, 25 Jan 2016 00:11:43 +0100 lee <l...@yagibdah.de> wrote: > Shlomi Fish <shlo...@shlomifish.org> writes: > > >> > > >> > In scalar context the comma operator evaluates its left-hand side, > >> > throws it away and returns the right-hand side. > >> > >> What is the useful use for this operator? > >> > > > > Well, I believe its use was originally inherited from > > https://en.wikipedia.org/wiki/C_%28programming_language%29 where one can do > > something like: > > > > x = (y++, y+2); > > > > In Perl 5 though it is preferable to use do { ... } instead: > > > > $x = do { $y++; $y+2; }; > > > > See http://perldoc.perl.org/functions/do.html . GCC and compatible compilers > > have a similar feature to Perl 5's do {...} called statement expressions: > > https://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html . > > How's that useful? Isn't that equivalent to > > $x = $y + 3; > > ? Well, it also changes the value of $y. You can use more complicated examples, and this was just for the sake of demonstration. One common pattern I used is to do: my %cache; sub f { return $cache{$result} //= do { # Calculate the cached result here. }; } > > I'm surprised that this apparently is supposed to evaluate to something, > though. I wouldn't expect that from a control structure. > > >> > This means that the value of (1, 2, 3) in scalar context is 3, and this > >> > is what gets assigned to $list. > >> > > >> > What is not happening at all is the creation of a list of numbers and a > >> > calculation of its length. > >> > > >> > See also perldoc -q 'difference between a list and an array' > >> > >> How do you convert an array into a list? > >> > > > > You just put it in list context. For example (untested): > > > > sub f > > { > > print (@_); > > } > > > > my @input = (3, 44, 505, 6.6); > > > > f(@input); > > > > my @other_list = (5,@input,24); > > I'm not sure where the conversion of an array (non-static) into a list > (static) would take place in this example. > (5,@input,24) becomes (5,3,44,505,6.6,24). Regards, Shlomi Fish -- ----------------------------------------------------------------- Shlomi Fish http://www.shlomifish.org/ List of Text Processing Tools - http://shlom.in/text-proc Inigo Montoya: You seem a decent fellow. I hate to kill you. The Man in Black: You seem a decent fellow. I hate to die. — http://en.wikiquote.org/wiki/The_Princess_Bride_%28film%29 Please reply to list if it's a mailing list post - http://shlom.in/reply . -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
