The total number of ancestors of a type (direct or indirect) in the inheritance hierarchy.

This metric counts all the super types of a given reference type. It is an indication of how deeply embedded a type is in a given inheritance hierarchy.

This metric is often confused with the depth of inheritance hierarchy metric proposed by Chidamber and Kemerer. In particular, Patrick Smacchia's NDepend tool defines depth of inheritance to be the number of ancestors. Indeed, if the type hierarchy were a tree, the two definitions coincide. However, in the presence of interfaces, a type can have multiple immediate supertypes, and therefore there are multiple paths to Object. The depth is the length of the longest such path, whereas the present metric returns the number of types encountered on any such path.

Pre-packaged Query

Query name = "Semmle/Metrics/Types/Inheritance/RefTypes that have many ancestors in the type hierarchy"

Reports types that have more than 10 ancestors, in decreasing order, as a bar chart.

from MetricRefType t, int d
where t.fromSource() and d = t.getNumberOfAncestors() and d > 10
select t, d order by d desc

.QL Source of Metric

This metric is defined in the class MetricRefType. It reads as follows:

int getNumberOfAncestors() {
   result = count(this.getASupertype+())
}

The + operator in the above definition stands for the transitive closure: this.getASupertype() would just return the immediate ancestors of this. By taking the transitive closure, we also get the indirect ancestors.

References

Patrick Smacchia. NDepend (metrics exploration tool for .NET), 2007.