Member predicate MetricElement::getMaintainabilityIndex

The maintainability index is a composite number expressing the ease of maintainability of a program or one of its components.

In order to compute the maintainability index, a metric element needs to provide methods that compute the element’s Halstead volume, cyclomatic complexity, average number of lines of code, and its percentage of comments.

The default implementations in this class simply fail. Classes MetricRefType and MetricCallable provide concrete implementations.