powershell - unary increment operator within a string doesn't work -

suppose set variable, $i = 0, then

"-$i-" => "-0-" "-$($i)-" => "-0-" 

the above expect, fails:

"-$(++$i)-" => "--"  # expected "-1-" 

however, expressions work. example:

"-$(pwd)-" => "-c:\temp-" 

so what's going on here?

according documentation, expected behavior

the increment operator (++) increases value of variable 1. when use increment operator in simple statement, no value returned. view result, display value of variable, follows:

    c:\ps> $a = 7     c:\ps> ++$a     c:\ps> $a     8 

to force value returned, enclose variable , operator in parentheses, follows:

    c:\ps> $a = 7     c:\ps> (++$a)     8 

the shortest way around following statement:

"-$((++$i))-" #=> -4- 

since set of parentheses tell return value, opposed execute statement.