PowerShell - execute script block in specific scope

Question

I am trying to implement RSpec/Jasmine like BDD framework in Powershell (or at least research the potential problems with making one).

Currently I am having problems with implementing simple before/after functionality. Given

$ErrorActionPreference = "Stop"

function describe()
    {
    $aaaa = 0;
    before { $aaaa = 2; };
    after { $aaaa; }
    }

function before( [scriptblock]$sb )
    {
    & $sb
    }

function after( $sb )
    {
    & $sb
    }

describe

the output is 0, but I would like it to be 2. Is there any way to achieve it in Powershell (short of making $aaaa global, traversing parent scopes in script blocks till $aaaa is found, making $aaaa an "object" and other dirty hacks:) )

What I would ideally like is a way to invoke a script block in some other scope but I don't have a clue whether it is possible at all. I found an interesting example at https://connect.microsoft.com/PowerShell/feedback/details/560504/scriptblock-gets-incorrect-parent-scope-in-module (see workaround), but am not sure how it works and if it helps me in any way.

TIA

Yes, it is not quite like RSpec/Jasmine, probably because of the problems described above. I have a very limited experience with Pester, but IMHO Pester is a very limited framework, no after/before, no nested describes, broken matcher implementation etc. — mbergal
– mbergal, Commented Jul 29, 2012 at 7:51
I will definitely consider contributing, currently I am just evaluating the possibility of implementing a better version in PowerShell - it might be just impossible, and Pester is what it is because of the conscious design decisions made after considering PowerShell limitations. — mbergal
– mbergal, Commented Jul 29, 2012 at 7:56
My take on BDD framework for PowerShell: github.com/mbergal/Jester. Caution: work in progress — mbergal
– mbergal, Commented Nov 3, 2012 at 20:03

x0n · Accepted Answer · 2012-07-29 14:26:17Z

9

The call operator (&) always uses a new scope. Instead, use the dot source (.) operator:

$ErrorActionPreference = "Stop"

function describe()
    {
    $aaaa = 0;
    . before { $aaaa = 2; };
    . after { $aaaa; }
    }

function before( [scriptblock]$sb )
    {
    . $sb
    }

function after( $sb )
    {
    . $sb
    }

describe

Note the use of . function to invoke the function in same scope as where `$aaaa is defined.

answered Jul 29, 2012 at 14:26

x0n

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