Using Reference (Part 10)-- Perl Study Notes

Using Reference (Part 10)-- Perl Study Notes

Create explicit reference
  $sv="hello";
  @av=qw(1 2 hello);
  %hv=qw(k1 v1 k2 v2);
  $rs=\$sv; #create $sv reference named $rs;
  $ra=\@av; #create $av reference named $ra;
  $rh=\$hv; #create $hv reference named $rh;
  $ra->[0]; #return first value of the array;
  $rh->{"k1"}; #return value of k1 of the hash;
  $ra->[0,1,2]; # same as $ra->[2];
 
Create anonymous reference
  $rs=\"hello world";  # create an scalar referecne named $rs;
  $ra=[1,2,"hello"];   # create an array reference named $ra;
  $rh={"k1","v1","k2","v2"}; # create an hash reference named $rh;

Dereferencing
  must use @$sa,%$sh,$$ss to dereferce the array, hash and scalar variable
 
Querying a Reference
  $a=10;
  $ra=\$a;
  ref($a); return false since $a is a scalar not a referecne
  ref($ra); return SCALAR scine $ra is a scalar reference
 
Symbolic Reference
  $x=10;
  $var="x";
  $$var=30; # $var will be replaced by x. $$var=30 will look as $x=30
 
  $var="x";
  @$var=(1,2,3); # sets @x to (1,2,3)
  It is important to note that symbolic references work only for global variables
 
Subroutine References
  References to Named Subroutines
  sub great{
    print "hello world\n";
    }
 
  $rs=\&grett; # create a reference to subroutine great
  $rs=\&greet(); # this does not create a reference to subroute great but a reference to the return value
 
  References to Anonymous Subroutines
  $rs=sub{
        print "hello \n";
        }
 
  Dereferencing subroutine References
  &$rs(10,20); # call the subroutine indirectly
  $rs->(10,20);   #same as above
 
  Symbolic Reference
  sub foo { print "foo called\n"}
  $rs="foo";
  &$rs(); # call foo subroutine and print "foo called"