quick study

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun One who is able to memorize something easily and quickly or is able to understand and deal with something easily and successfully.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun obsolete an actor who is able to learn their lines in a short amount of time
• noun one who is capable of learning at a fast pace; a fast learner

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun someone able to acquire new knowledge and skills rapidly and easily