Think Perl 6

Chapter 11. Case Study: Data Structure Selection

At this point you have learned about Perl’s core data structures, and you have seen some of the algorithms that use them.

This chapter presents a case study with exercises that let you think about choosing data structures and practice using them.

But first, I would like to briefly introduce two conditional structures that have been left aside so far and provide a couple of new possibilities about subroutine signatures.

The Ternary Conditional Operator

Consider the following code that tests the value of a positive integer:

my $result;
if $num < 10 {
    $result = "One digit";
} else {
    $result = "More than one digit";
}
say $result;

This is quite simple, but a bit long. This can be rewritten in just one line of code:

say $num < 10 ?? "One digit" !! "More than one digit";

The operator is in two parts: the ?? and the !!, which separate three expressions (hence the name “ternary operator”):

• The condition to be evaluated (is $num less than 10?)

• The expression defining the value if the condition is true

• The expression defining the value if the condition is false

This statement checks if $num is less than 10 and, if true, prints “"One digit”; if the condition is false, it prints “More than one digit.”

This operator does not provide any new functionality; it just offers a more concise syntax.

It is possible to nest several ternary operators to examine successively multiple choices:

say $value < 10 ?? "One digit" !! $value < 100 ?? "Two digits" !! $value ...