ЭЛЕКТРОННАЯ БИБЛИОТЕКА КОАПП |
Сборники Художественной, Технической, Справочной, Английской, Нормативной, Исторической, и др. литературы. |
8.5 Private Variables in FunctionsWe've already talked about the sub add { my $sum; # make $sum a local variable $sum = 0; # initialize the sum foreach $_ (@_) { $sum += $_; # add each element } return $sum; # last expression evaluated: # the sum of elements } When the first body statement is executed, any current value of the global variable Here's a way to create a list of all the elements of an array greater than 100: sub bigger_than_100 { my (@result); # temporary for holding the return value foreach $_ (@_) { # step through the arg list if ($_ > 100) { # is it eligible? push(@result,$_); # add it } } return @result; # return the final list } What if we wanted all elements greater than 50, rather than all elements greater than 100? We'd have to edit the program, changing each 100 to 50. But what if we need both? Well, we can replace the 50 or 100 with a variable reference instead. This change makes the program look like: sub bigger_than { my($n,@values); # create some local variables ($n,@values) = @_; # split args into limit and values my(@result); # temporary for holding the return value foreach $_ (@values) { # step through the arg list if ($_ > $n) { # is it eligible? push(@result,$_); # add it } } @result; # return the final list } # some invocations: @new = bigger_than(100,@list); # @new gets all @list > 100 @this = bigger_than(5,1,5,15,30); # @this gets (15,30) Notice that this time, we used two additional local variables to give names to arguments. This method is fairly common in practice - you can more easily talk about The result of my($n,@values); ($n,@values) = @_; # split args into limit and values with: my($n,@values)= @_; This is, in fact, a very common Perl-ish thing to do. Local nonargument variables can be given literal values in the same way, such as: my($sum) = 0; # initialize local variable Be warned that despite its appearance as a declaration, |