How should you handle nested functions? [closed] - function

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What's the proper way to call a function in PowerShell?
Example 1:
Function Divide
{
Return ($a / $b)
}
Function GetNumbers
{
$a = Read-Host "Dividend"
$b = Read-Host "Divisor"
Divide
}
GetNumbers
Example 2:
Function Divide
{
Param
(
[Int]$Dividend,
[Int]$Divisor
)
Return ($Dividend / $Divisor)
}
Function GetNumbers
{
$a = Read-Host "Dividend"
$b = Read-Host "Divisor"
Divide -Dividend $a -Divisor $b
}
GetNumbers
I mean, why should I use the Param part when I can access the parent function's variables? Or is that just bad programming?

Answer 1

The problem with the first example is that your Divide function will only work if it happens to be inside the GetNumbers function. If you try to call it outside of GetNumbers, you will raise an error because $a and $b will be undefined:
PS > Divide
Attempted to divide by zero.
At line:3 char:12
+ Return ($a / $b)
+ ~~~~~~~~~
+ CategoryInfo : NotSpecified: (:) [], RuntimeException
+ FullyQualifiedErrorId : RuntimeException
This means the use case of your Divide function is very limited and also somewhat unintuitive. People may call the function thinking it will work (since it is at module-level) and be surprised by the results.
The Divide function in the second example however does not have this issue. It is independent of the GetNumbers function and can be used anywhere a normal function can. This has three advantages:
Divide behaves as a module-level function should, which means there are no nasty surprises for your users.
The use case of Divide has been greatly enhanced. You can now divide two numbers anywhere you need to.
Your code is more robust. Divide does not need to be inside a function which just happens to define two variables named $a and $b which just happen to be numbers (see how fragile the first example is?).
Note too that you do not need to explicitly give the parameter names in your second example. You could just do:
Divide $a $b
And if you dislike the size of the second Divide function, you could always make your Param statement less spread out:
Function Divide
{
Param ([Int]$Dividend, [Int]$Divisor)
Return ($Dividend / $Divisor)
}