Hashes

In the array, indexes are integer numbers starting from zero. Hashes are another structural type of data in Perl 6 that can be treated as arrays whose indices are strings.

Hashes use the % sigil. Other names for hashes from various programming languages are associative arrays, dictionaries or dicts, and maps. Hashes are very useful when you need to keep a few values together. For example, take a look at the following code snippet:

my %city = 
    name => 'London',
    country => 'gb',
    latitude => 51.52,
    longitude => 0,
    area => 1577,
    inhabitants => 8_700_000;

Elements of the hash are pairs, which are in turn two things—the key and the value. In this example, keys of the %city hash are name, country, and so on, and their values are London and gb.

The layout of the code in such assignments may be changed to align the keys and the values, as you can see here:

my %city = 
    name        => 'London',
    country     => 'gb',
    latitude    => 51.52,
    longitude   => 0,
    area        => 1577,
    inhabitants => 8_700_000;

In the assignment, pairs of the hash can be surrounded in parentheses, as shown here:

my %city = (
    name => 'London',
    country => 'gb',
    latitude => 51.52,
    longitude => 0,
    area => 1577,
    inhabitants => 8_700_000);

When a hash is printed (say %city), it is displayed in a pair of curly braces, as shown in the following lines of code:

{area => 1577, country => gb, inhabitants => 8700000,    
latitude => 51.52, longitude => 0, name => London}

If there are keys with identical names, then the last one wins. Consider the following hash creation:

my %city = 
    name => 'London',
    name => 'Paris';
say %city;

This program prints {name => Paris} only.

The information in this section is enough to continue on our way to learning types in Perl 6.