= Solution
Count each invocation before delegating, including duplicate insertions, and reset after clearing:
``
class IntegerSetWithCount extends IntegerSet() {
private var attempts = BigInt(0)
override def insert(x: Int): Unit = {
attempts += 1
super.insert(x)
}
override def clear: Unit = {
super.clear
attempts = BigInt(0)
}
def getCount: BigInt = attempts
}
``
The inherited implementation already maintains `size`; the new counter measures insertion attempts, not successful increases in <cardinality>. Deletion and popping do not subtract from it. Incrementing before delegation also counts an attempted insertion that subsequently fails a capacity check. <Arbitrary-precision arithmetic> avoids silently wrapping the historical count, though its arithmetic is not constant-cost for arbitrarily large counts.
As the source supplies no <object constructor> signature for the concrete set, this code uses a fresh default-constructible `IntegerSet`, with matching default capacity. Its correct behavior also assumes the base implementation does not internally invoke these overridable operations in a way that interferes with the counter. Part e exhibits that dependency.
\b[Source-signature qualification for the following set implementations:] the intended membership query must be declared `def contains(x: Int): Boolean`. The printed abstract declaration omits its result type; interpreted literally as <Scala> 2 procedure syntax, it returns `Unit`. The solutions use the explicit Boolean query contract, and `Unit` for the two mutators. Parameterless `clear` is overridden without adding parentheses.<Scala 2.13 basic declarations and definitions specification>[Procedures: a method declaration omitting its result type implicitly has Unit result]{ref}
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