Friday, June 19, 2015

c++ parametrized functor - more learning notes

Parametrized Functor (class template) is a standard, recommended construct in c++, with no counterpart in java. C# delegae is conceptually simpler but internally more complex IMO, and represents a big upgrade from c++ functor. Better get some clarity with functor before comparing with delegates.

The #1 most common functor is the stateless functor (like a simple lambda). The 2nd common category is the (stateful) immutable functor. In all cases, the functor is designed for pass-by-value (not by ref or by pointer), cheap to copy, cheap to construct. I see many textbook code samples creating throwaway functor instances.

Example of the 2nd category - P127[[essentialC++]].

A) One mental block is using a simple functor Class as a template type param. This is different from java/c#

B) One mental block is a simple parametrized functor i.e. class template. C++ parametrized functor can take various type params, more "promiscuous" than c#/java.

C) A bigger mental block, combining A+B, is a functor parametrized with another functor Class as a template param. See P186[[EssentialC++]]. This is presented as a simple construct, with about 20 lines of code, but the more I look at it, the more strange it feels.

In java, we write a custom comparitor class rather than a comparitor class Template. We also have the simpler alternative of a Comparable interface, but that's not very relevant in this discussion. Java 8 lambda -- http://www.dreamsyssoft.com/java-8-lambda-tutorial/comparator-tutorial.php

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