Expression

Expression Grouping

() is grouping expression that allows assignment/add higher execution precedence within it and pass through the value to outer context. It's worth noting that () does not allow to eval a control flow statement which is very counter-intuitive.

# enforce precedence
(1 + 2) * 3 # 9
# inline assignment
($foo = 1) # 1
# eval a statement
($null = if ($true) { "foo" }) # foo

(if ($true) { "foo" }) # parsing error! #

IMPORTANT

() only allows one single expression within it.

Sub-Expression

$() is yet another way to eval a expression to value but suppress the output of assignment statement.

$(if ($true) { "foo" }) # foo

# assignment does not pass through value to outer context
$($foo = 1 -gt 3) # $null

# self increment is another special kind of assignment
$($i++) # $null

Since $() has a nature of suppressing value from assignment statement, we can use it as a single calculation block.

$foo = 1
# custom calculation block
$(
    $foo = 1 + 2
    # self operation is also suppressed even though it should output
    $foo++

    $foo
    $foo # yield more than once
).Length # 2

Array Sub-Expression

@() is almost the same as $() but ensures the output as an array, no matter how few items were popped from the expression.

@($pwd).GetType().Name # Object[]
$($pwd).GetType().Name # PathInfo