Setting the topic with given

In the example in the previous section, we used a chained if—elsif construction. Let's take a look at this once again:

if    $step eq 'up'      {$y--}
elsif $step eq 'down'    {$y++}
elsif $step eq 'right'   {$x++}
elsif $step eq 'left'    {$x--}
elsif $step eq 'take-it' {take @matrix[$y][$x]}

It is clearly seen that all the branches contain the same code, which compares the current value of the $step variable with one of the predefined values. While being simple and straightforward, this is not the most elegant way of doing such comparisons.

In some languages such as C and C++, the switch and case keywords help reorganize the if-else chain. In Perl 6, we use given and when. The preceding code can be rewritten in the following way:

given $step {
    when 'up'      {$y--}
    when 'down'    {$y++}
    when 'right'   {$x++}
    when 'left'    {$x--}
    when 'take-it' {take @matrix[$y][$x]}
}

What happens here is that given takes the $step variable and makes it the...