1. Perl Chapter 5 part 2 references / nested structures

2. References 3 rd kind of scalar value related to pointers (addresses) used to make complex data structures

3. Hard references A variable storing a reference which is set using the \ operator $sum=0; @list=(1, 3, 5, 7); $ref_sum = \$sum; $ref_list = \@list; Can also point to literals $ref_pi = \3.14159; $ref_list = [1,3,5,7]; #yes, brackets! $ref_hash={‘Bob’=>’42’, ‘Jake’=>’12’, ‘Darcie’=>’11’}; #yes, braces! What principle violated by [] and {}? Hint: Things shouldn’t be used for difference purposes.

4. Dereferencing Explicit in Perl Used to get value at that address Several ways – 1 st way $$ $sum = 17; $ref_sum = \$sum; print “The sum is $$ref_sum\n” if missing $  SCALAR (0xb75d3d) a hex address

5. 2 nd way uses infix operator -> $ref_list=[1, 3, 5, 7]; $$ref_list[3]=17; $ref_list->[3]=17; $ref_hash={‘Bob’=>’42’,‘Jake’=>’12’, ‘Darcie’=>’11’}; $$ref_hash{‘Bob’} = ‘43’; $ref_hash->{‘Bob’}=‘43’;

6. Soft references $sum_name=“sum”; $$sum_name=17; same as $sum = 17; Called a symbolic reference Can be dangerous – can be created accidently by a typo – turn off using pragma use strict ‘refs’; – flags all symbolic references in enclosing block

7. Nested Data Structures THE PURPOSE of references To simulate a 2D array @row1 = (1,3,5); @row2=(7,9,11); @row3=(13, 15,17); @mat=(\@row1, \@row2, \@row3); To access element $mat[2]->[3] or $$mat[2][3]

8. Notes In Perl, array of refs to arrays NOT same as ref to array of refs to array Any row can have any length, SO simulates irregular arrays

9. hashes of … Can also have hashes of arrays, hashes of hashes, arrays of hashes, etc… Hash of hashes

10. %teams=( Broncos=>{Quarterback=> “Cutler”, Runningback => “Hall”, Tightend=> “Graham”, }, Colts=>{Quarterback=>”Manning”, DefensiveEnd=>”Dawson”, Tightend=>”Clark”, }, : ) DEMO hashex.pl

11. Print out hash of hash while (($team, $position_ref)= each %teams) { print “$team:”; while (($position,$player)= each $position_ref){ print “$position: $player”; } print “\n”; }