You can do this:
| stats count | eval foo = "bar" | stats values(count), [stats count as search | eval search = "values(foo)"]
Essentially, the second function and/or field name are evaluated and returned by the subsearch. Adding the
values() within the subsearch seems to be necessary to not run into any errors, at least based on my quick testing.
In addition, read https://answers.splunk.com/answers/129424/how-to-compare-fields-over-multiple-sourcetypes-without-jo... and watch the March 2016 virtual.conf talk from http://wiki.splunk.com/Virtual_.conf for more info how this can be done without subsearches 😉