Can a beer drinking so called functional alcoholic and pot smoker effectively quit without in patient rehab?

Yes: Neither of these require inpatient detoxification if you are healthy. I would recommend alcoholics anonymous and working with your physician to make sure you don't have medical problems that require you to be under the care of a physician.

Anybody can quit: Many people stop drinking and drugging without any formal help whatsoever. Some do it through self help groups like aa or na, or smart recovery and lifering secular recovery. Others do it through their religious beliefs and even through increasing involvement in other healthier activities (alice cooper quit through golf). Outpatient treatment is highly effective, with inpatient when this fails.

Most people don't : Have the luxury of inpatient substance abuse rehabilitation. If you need to detoxify - that should be done under medical supervision. Alcoholics anonymous & narcotics anonymous are exceptional 12 step programs that form an excellent base for a recovery program. Working with an addiction medicine specialist is also beneficial.