bash behavior for command evaluation in func

behavior.bash

## I expect this to fail when string passed as first argument
"bash -i -c 'echo hello world'"
#>bash: bash -i -c 'echo hello world': command not found...

## I expect this to fail when string " is around ${@}, but well...
$ function asdf() { "${@}"; }
$ asdf bash -i -c 'echo hello world'
#>hello world

## I expect an empty string value
$ : ${x:=""}
#> x == ""

## I expect an empty string value as well, but...
$ : ${y:=''}
#> x== "''"    or in other words, two literal '