ЭЛЕКТРОННАЯ БИБЛИОТЕКА КОАПП |
Сборники Художественной, Технической, Справочной, Английской, Нормативной, Исторической, и др. литературы. |
8.4 ArgumentsAlthough subroutines that have one specific action are useful, a whole new level of usefulness becomes available when you can pass arguments to a subroutine. In Perl, the subroutine invocation is followed by a list within parentheses, causing the list to be automatically assigned to a special variable named sub say_hello_to { print "hello, $_[0]!\n"; # first parameter is target } Here, we see a reference to say_hello_to("world"); # gives hello, world! $x = "somebody"; say_hello_to($x); # gives hello, somebody! say_hello_to("me")+ say_hello_to("you"); # and me and you Note that in the last line, the return values weren't really used. But in evaluating the sum, Perl has to evaluate all of its parts, so the subroutine was invoked twice. Here's an example using more than one parameter: sub say { print "$_[0], $_[1]!\n"; } say("hello","world"); # hello world, once again say("goodbye","cruel world"); # silent movie lament Excess parameters are ignored: if you never look at The Let's revisit that "add a and b" routine from the previous section. Here's a subroutine that adds any two values, specifically, the two values passed to the subroutine as parameters: sub add_two { return $_[0] + $_[1]; } print add_two(3,4); # prints 7 $c = add_two(5,6); # $c gets 11 Now let's generalize this subroutine. What if we had 3, 4, or 100 values to add together? We could do it with a loop, like so: sub add { $sum = 0; # initialize the sum foreach $_ (@_) { $sum += $_; # add each element } return $sum; # last expression evaluated: sum of all elements } $a = add(4,5,6); # adds 4+5+6 = 15, and assigns to $a print add(1,2,3,4,5); # prints 15 print add(1..5); # also prints 15, because 1..5 is expanded What if we had a variable named |