Firstly, please note Duck typing
(see Sean Corfields excellent presentation
) is NOT primarily about performance. In most cases this is probably the least interesting aspect of it. Using duck typing to improve performance before identifying a performance bottleneck is a sure sign of Premature Optimization
Once you have a working application with a performance bottleneck which can be attributed to a large number of method calls each of which does a relatively small amount of processing, it is time to consider taking advantage of duck typing to improve the performance . . .