Mixed-objects

Mixed objects

In PowerShell v2 it is possible to operate on properties Count and Length assuming they get null if missed and null is converted to 0 where a number is expected. The below example calculates the total size of the current directory:

    $totalLength = 0
    Get-ChildItem -Force -Recurse | %{
        $totalLength += $_.Length
    }

Length gets the file length for file items and gets 0 (converted null) for directory items because directory items do not have the property Length.

In PowerShell v3 any object has properties Count and Length. For nulls they get 0. For objects with native Count or Length their values are returned. For other objects they get 1, not null.

As a result, in the above code 1 is added to the sum for each directory item.

This feature makes it more difficult to work with heterogeneous collections where some objects have their native Count or Length and some do not. It is not possible to assume that 0 and missing is logically the same.

The script Test-DirectorySize.ps1 calculates a directory size using two methods. Results are different in different versions.

---

• Microsoft Connect 793560