Code Quality

First: Which aspect of code quality am I concerned with here? Of all the qualities that code has correctness takes pride of place, if it is not correct not a lot else matters. However, this is not what most people assume by the phrase "code quality" since it is assumed as a basic attribute, rather than a distinguishing attribute. Then there are the performance qualities, time and space. Given Moore's Law (even after running off the end of it for speed), optimizing compilers, and other advances this is not an issue in the small. If there are performance issues they need to be addressed (in the absence of pathology) with algorithmic and architectural attacks.

For me, the prime code quality issue that is contentious enough to write about is comprehensibility. If people can read the code it will be maintainable, portable, and all the other things that people want in code when they are looking at it.

What drives comprehensibility? Or, to flip the question, what drives incomprehensibility? In computer programs the primary barrier to understanding is complexity. One of the primary controllable factors driving complexity is scale (this also applies to looking at computer systems and projects at higher levels).

To reduce complexity, reduce the scale.

This means that computer programs need to be factored into small subroutines. Keeping routines small requires constructing them from lower level abstractions. Identifying those abstractions and designing good interfaces for them are the primary skills required to create good code.