Demonstrates creating a custom Cocoa Key Value Coding Collection Operator
According to Apple's documentation:
"Note: It is not currently possible to define your own collection operators."
But that's just not entirely true.
This demo just adds a NSArray category (NSArray+KVCCustom.h) just to provide the implementation of a selector matching the format "{Collector name}ForKeyPath:", which you can then use via [instance valueForKeyPath:@"@{Collector name}.{property}"] to reduce some array of objects to a scalar value.