Scope, shared objects, and module boundaries

The idea

PowerShell can find variables in an enclosing scope, but an ordinary assignment in a child scope normally creates or updates a local binding. Running a scriptblock with the call operator uses a child scope; dot-sourcing runs it in the current scope instead. These choices affect which names a helper can leave behind and whether a local assignment changes a caller-visible variable.

Scope does not automatically clone the objects referenced by variables. A child scope can obtain a reference to a mutable hashtable and change its contents even when it never rebinds the parent’s variable. Modules add a useful boundary for private implementation state and exported functions. Prefer explicit parameters and return values for ordinary communication, and document shared mutable state where it is intentional.

$value = 3
& { $value = 8; $value }
$value
$box = @{ Count = 1 }
& { $box.Count = 4 }
$box.Count

8
3
4

The child assignment creates a local value binding. The hashtable mutation changes the shared object referenced by box.