Identifier length and limited programmer memory

• Authors: Dave Binkley;Dawn Lawrie;Steve Maex;Christopher Morrell
• Venue: Science of Computer Programming
• Year: 2009

Because early variable mnemonics were limited to as few as six to eight characters, many early programmers abbreviated concepts in their variable names. The past thirty years have seen a steady increase in permitted name length and, slowly, an increase in the actual identifier length. However, in theory names can be too long for programmers to comprehend and manipulate effectively. Most obviously, in object-oriented programs, entity naming often involves chaining of method calls and field selectors (e.g., class.firstAssignment().name.trim()). While longer names bring the potential for better comprehension through more embedded sub-words, there are practical limits to their length given limited human memory resources. The driving hypothesis behind the presented study is that names used in modern programs have reached this limit. Thus, a goal of the study is to better understand the balance between longer, more expressive names and limited programmer memory resources. Statistical models derived from an experiment involving 158 programmers of varying degrees of experience show that longer names extracted from production code take more time to process and reduce correctness in a simple recall activity. This has clear negative implications for any attempt to read, and hence comprehend or manipulate, the source code found in modern software. The experiment also evaluates the advantage of identifiers having probable ties to a programmer's persistent memory. Combined, these results reinforce past proposals advocating the use of limited, consistent, and regular vocabulary in identifier names. In particular, good naming limits individual name length and reduces the need for specialized vocabulary.