Setting a default value for $@ (sh vs dash vs ksh vs bash)

test.sh

#!/bin/sh
#!/bin/ksh
#!/usr/pkg/bin/dash
#!/usr/pkg/bin/bash

somefn() {
  local args="${@:-something}"
  echo "Value of \$args: $args"
}

# prints "something"
somefn

# prints "foo" in every shell but bash, where it prints "foo bar"
somefn foo bar