Design Patterns in Dynamic Languages–PowerShell

I was Googling for the Strategy Pattern and implementations done in dynamic languages and came across Neal Ford’s slides where he implements it in Groovy. Here are Peter Norvig’s slides, Design Patterns in Dynamic Languages, in it he states that 16 of the 23 GoF patterns have qualitatively simpler implementations in dynamic languages. Mr. Norvig is Director of Research at Google.

One of Neal Ford’s slides captures the idea.

The Strategy Pattern

Formally speaking, the strategy pattern defines a family of algorithms, encapsulates each one, and makes them interchangeable. Strategy lets the algorithm vary independently from clients that use it.

function ql {$args}            
            
function CalcByMult {            
    param($n,$m)             
            
    $n*$m            
}            
            
function CalcByManyAdds {            
    param($n,$m)            
                
    1..$n | % {$result = 0} { $result += $m } {$result}            
}            
            
            
$sampleData = @(            
    ,(3,4,12)            
    ,(5,-5,-25)            
)            
             
$strategies = ql CalcByMult CalcByManyAdds            
             
foreach($Dataset in $sampleData) {            
    foreach($strategy in $strategies) {            
        $Dataset[2] -eq (& $strategy $Dataset[0] $Dataset[1])            
    }            
}

Why Bother with Extra Structure?

Here I am creating an array of PowerShell script blocks for the strategies, eliminating the ceremony of naming them.

$sampleData = @(            
    ,(3,4,12)            
    ,(5,-5,-25)            
)            
             
$strategies =             
{param($n,$m) $n*$m},            
{            
    param($n,$m)            
    1..$n | % {$result = 0} { $result += $m } {$result}            
}            
             
foreach($Dataset in $sampleData) {            
    foreach($strategy in $strategies) {            
        $Dataset[2] -eq (& $strategy $Dataset[0] $Dataset[1])            
    }            
}